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- Committer: Bazaar Package Importer
- Author(s): Jonathan Riddell
- Date: 2006-11-14 22:45:03 UTC
- mfrom: (1.1.7 upstream)
- Revision ID: james.westby@ubuntu.com-20061114224503-t1rr58e2xv9hzd0u
Tags: 4:3.5.5a.dfsg.1-3ubuntu1
* Merge with Debian
* Add --enable-gcc-hidden-visibility
* Delta from Deban in KUBUNTU-DEBIAN-CHANGES
* Add --enable-gcc-hidden-visibility
* Delta from Deban in KUBUNTU-DEBIAN-CHANGES
- files added:
- debian/not-installed.list
- files removed:
- debian/DIFF
- files modified:
- Makefile.in
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kioslave/http/kcookiejar/rfc2965
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Network Working Group D. Kristol
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Request for Comments: 2965 Bell Laboratories, Lucent Technologies
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Obsoletes: 2109 L. Montulli
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Category: Standards Track Epinions.com, Inc.
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October 2000
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HTTP State Management Mechanism
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Status of this Memo
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This document specifies an Internet standards track protocol for the
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Internet community, and requests discussion and suggestions for
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improvements. Please refer to the current edition of the "Internet
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Official Protocol Standards" (STD 1) for the standardization state
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and status of this protocol. Distribution of this memo is unlimited.
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Copyright Notice
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Copyright (C) The Internet Society (2000). All Rights Reserved.
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IESG Note
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The IESG notes that this mechanism makes use of the .local top-level
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domain (TLD) internally when handling host names that don't contain
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any dots, and that this mechanism might not work in the expected way
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should an actual .local TLD ever be registered.
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Abstract
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This document specifies a way to create a stateful session with
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Hypertext Transfer Protocol (HTTP) requests and responses. It
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describes three new headers, Cookie, Cookie2, and Set-Cookie2, which
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carry state information between participating origin servers and user
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agents. The method described here differs from Netscape's Cookie
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proposal [Netscape], but it can interoperate with HTTP/1.0 user
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agents that use Netscape's method. (See the HISTORICAL section.)
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This document reflects implementation experience with RFC 2109 and
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obsoletes it.
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1. TERMINOLOGY
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The terms user agent, client, server, proxy, origin server, and
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http_URL have the same meaning as in the HTTP/1.1 specification
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[RFC2616]. The terms abs_path and absoluteURI have the same meaning
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as in the URI Syntax specification [RFC2396].
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Kristol & Montulli Standards Track [Page 1]
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RFC 2965 HTTP State Management Mechanism October 2000
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Host name (HN) means either the host domain name (HDN) or the numeric
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Internet Protocol (IP) address of a host. The fully qualified domain
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name is preferred; use of numeric IP addresses is strongly
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discouraged.
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The terms request-host and request-URI refer to the values the client
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would send to the server as, respectively, the host (but not port)
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and abs_path portions of the absoluteURI (http_URL) of the HTTP
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request line. Note that request-host is a HN.
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The term effective host name is related to host name. If a host name
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contains no dots, the effective host name is that name with the
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string .local appended to it. Otherwise the effective host name is
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the same as the host name. Note that all effective host names
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contain at least one dot.
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The term request-port refers to the port portion of the absoluteURI
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(http_URL) of the HTTP request line. If the absoluteURI has no
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explicit port, the request-port is the HTTP default, 80. The
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request-port of a cookie is the request-port of the request in which
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a Set-Cookie2 response header was returned to the user agent.
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Host names can be specified either as an IP address or a HDN string.
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Sometimes we compare one host name with another. (Such comparisons
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SHALL be case-insensitive.) Host A's name domain-matches host B's if
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* their host name strings string-compare equal; or
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* A is a HDN string and has the form NB, where N is a non-empty
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name string, B has the form .B', and B' is a HDN string. (So,
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x.y.com domain-matches .Y.com but not Y.com.)
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Note that domain-match is not a commutative operation: a.b.c.com
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domain-matches .c.com, but not the reverse.
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The reach R of a host name H is defined as follows:
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* If
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- H is the host domain name of a host; and,
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- H has the form A.B; and
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- A has no embedded (that is, interior) dots; and
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- B has at least one embedded dot, or B is the string "local".
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then the reach of H is .B.
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Kristol & Montulli Standards Track [Page 2]
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RFC 2965 HTTP State Management Mechanism October 2000
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* Otherwise, the reach of H is H.
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For two strings that represent paths, P1 and P2, P1 path-matches P2
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if P2 is a prefix of P1 (including the case where P1 and P2 string-
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compare equal). Thus, the string /tec/waldo path-matches /tec.
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Because it was used in Netscape's original implementation of state
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management, we will use the term cookie to refer to the state
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information that passes between an origin server and user agent, and
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that gets stored by the user agent.
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1.1 Requirements
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The key words "MAY", "MUST", "MUST NOT", "OPTIONAL", "RECOMMENDED",
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"REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT" in this
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document are to be interpreted as described in RFC 2119 [RFC2119].
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2. STATE AND SESSIONS
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This document describes a way to create stateful sessions with HTTP
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requests and responses. Currently, HTTP servers respond to each
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client request without relating that request to previous or
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subsequent requests; the state management mechanism allows clients
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and servers that wish to exchange state information to place HTTP
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requests and responses within a larger context, which we term a
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"session". This context might be used to create, for example, a
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"shopping cart", in which user selections can be aggregated before
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purchase, or a magazine browsing system, in which a user's previous
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reading affects which offerings are presented.
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Neither clients nor servers are required to support cookies. A
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server MAY refuse to provide content to a client that does not return
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the cookies it sends.
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3. DESCRIPTION
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We describe here a way for an origin server to send state information
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to the user agent, and for the user agent to return the state
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information to the origin server. The goal is to have a minimal
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impact on HTTP and user agents.
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3.1 Syntax: General
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The two state management headers, Set-Cookie2 and Cookie, have common
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syntactic properties involving attribute-value pairs. The following
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grammar uses the notation, and tokens DIGIT (decimal digits), token
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Kristol & Montulli Standards Track [Page 3]
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RFC 2965 HTTP State Management Mechanism October 2000
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(informally, a sequence of non-special, non-white space characters),
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and http_URL from the HTTP/1.1 specification [RFC2616] to describe
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their syntax.
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av-pairs = av-pair *(";" av-pair)
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av-pair = attr ["=" value] ; optional value
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attr = token
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value = token | quoted-string
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Attributes (names) (attr) are case-insensitive. White space is
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permitted between tokens. Note that while the above syntax
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description shows value as optional, most attrs require them.
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NOTE: The syntax above allows whitespace between the attribute and
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the = sign.
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3.2 Origin Server Role
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3.2.1 General The origin server initiates a session, if it so
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desires. To do so, it returns an extra response header to the
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client, Set-Cookie2. (The details follow later.)
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A user agent returns a Cookie request header (see below) to the
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origin server if it chooses to continue a session. The origin server
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MAY ignore it or use it to determine the current state of the
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session. It MAY send back to the client a Set-Cookie2 response
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header with the same or different information, or it MAY send no
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Set-Cookie2 header at all. The origin server effectively ends a
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session by sending the client a Set-Cookie2 header with Max-Age=0.
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Servers MAY return Set-Cookie2 response headers with any response.
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User agents SHOULD send Cookie request headers, subject to other
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rules detailed below, with every request.
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An origin server MAY include multiple Set-Cookie2 headers in a
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response. Note that an intervening gateway could fold multiple such
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headers into a single header.
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Kristol & Montulli Standards Track [Page 4]
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RFC 2965 HTTP State Management Mechanism October 2000
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3.2.2 Set-Cookie2 Syntax The syntax for the Set-Cookie2 response
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header is
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set-cookie = "Set-Cookie2:" cookies
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cookies = 1#cookie
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cookie = NAME "=" VALUE *(";" set-cookie-av)
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NAME = attr
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VALUE = value
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set-cookie-av = "Comment" "=" value
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| "CommentURL" "=" <"> http_URL <">
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| "Discard"
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| "Domain" "=" value
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| "Max-Age" "=" value
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| "Path" "=" value
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| "Port" [ "=" <"> portlist <"> ]
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| "Secure"
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| "Version" "=" 1*DIGIT
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portlist = 1#portnum
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portnum = 1*DIGIT
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Informally, the Set-Cookie2 response header comprises the token Set-
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Cookie2:, followed by a comma-separated list of one or more cookies.
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Each cookie begins with a NAME=VALUE pair, followed by zero or more
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semi-colon-separated attribute-value pairs. The syntax for
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attribute-value pairs was shown earlier. The specific attributes and
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the semantics of their values follows. The NAME=VALUE attribute-
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value pair MUST come first in each cookie. The others, if present,
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can occur in any order. If an attribute appears more than once in a
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cookie, the client SHALL use only the value associated with the first
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appearance of the attribute; a client MUST ignore values after the
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first.
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The NAME of a cookie MAY be the same as one of the attributes in this
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specification. However, because the cookie's NAME must come first in
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a Set-Cookie2 response header, the NAME and its VALUE cannot be
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confused with an attribute-value pair.
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NAME=VALUE
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REQUIRED. The name of the state information ("cookie") is NAME,
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and its value is VALUE. NAMEs that begin with $ are reserved and
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MUST NOT be used by applications.
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The VALUE is opaque to the user agent and may be anything the
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origin server chooses to send, possibly in a server-selected
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printable ASCII encoding. "Opaque" implies that the content is of
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interest and relevance only to the origin server. The content
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may, in fact, be readable by anyone that examines the Set-Cookie2
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header.
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Kristol & Montulli Standards Track [Page 5]
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RFC 2965 HTTP State Management Mechanism October 2000
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Comment=value
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OPTIONAL. Because cookies can be used to derive or store private
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information about a user, the value of the Comment attribute
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allows an origin server to document how it intends to use the
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cookie. The user can inspect the information to decide whether to
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initiate or continue a session with this cookie. Characters in
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value MUST be in UTF-8 encoding. [RFC2279]
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CommentURL="http_URL"
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OPTIONAL. Because cookies can be used to derive or store private
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information about a user, the CommentURL attribute allows an
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origin server to document how it intends to use the cookie. The
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user can inspect the information identified by the URL to decide
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whether to initiate or continue a session with this cookie.
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Discard
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OPTIONAL. The Discard attribute instructs the user agent to
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discard the cookie unconditionally when the user agent terminates.
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Domain=value
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OPTIONAL. The value of the Domain attribute specifies the domain
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for which the cookie is valid. If an explicitly specified value
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does not start with a dot, the user agent supplies a leading dot.
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Max-Age=value
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OPTIONAL. The value of the Max-Age attribute is delta-seconds,
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the lifetime of the cookie in seconds, a decimal non-negative
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integer. To handle cached cookies correctly, a client SHOULD
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calculate the age of the cookie according to the age calculation
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rules in the HTTP/1.1 specification [RFC2616]. When the age is
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greater than delta-seconds seconds, the client SHOULD discard the
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cookie. A value of zero means the cookie SHOULD be discarded
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immediately.
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Path=value
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OPTIONAL. The value of the Path attribute specifies the subset of
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URLs on the origin server to which this cookie applies.
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Port[="portlist"]
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OPTIONAL. The Port attribute restricts the port to which a cookie
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may be returned in a Cookie request header. Note that the syntax
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REQUIREs quotes around the OPTIONAL portlist even if there is only
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one portnum in portlist.
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Kristol & Montulli Standards Track [Page 6]
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RFC 2965 HTTP State Management Mechanism October 2000
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Secure
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OPTIONAL. The Secure attribute (with no value) directs the user
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agent to use only (unspecified) secure means to contact the origin
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server whenever it sends back this cookie, to protect the
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confidentially and authenticity of the information in the cookie.
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The user agent (possibly with user interaction) MAY determine what
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level of security it considers appropriate for "secure" cookies.
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The Secure attribute should be considered security advice from the
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server to the user agent, indicating that it is in the session's
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interest to protect the cookie contents. When it sends a "secure"
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cookie back to a server, the user agent SHOULD use no less than
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the same level of security as was used when it received the cookie
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from the server.
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Version=value
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REQUIRED. The value of the Version attribute, a decimal integer,
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identifies the version of the state management specification to
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which the cookie conforms. For this specification, Version=1
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applies.
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3.2.3 Controlling Caching An origin server must be cognizant of the
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effect of possible caching of both the returned resource and the
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Set-Cookie2 header. Caching "public" documents is desirable. For
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example, if the origin server wants to use a public document such as
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a "front door" page as a sentinel to indicate the beginning of a
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session for which a Set-Cookie2 response header must be generated,
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the page SHOULD be stored in caches "pre-expired" so that the origin
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server will see further requests. "Private documents", for example
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those that contain information strictly private to a session, SHOULD
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NOT be cached in shared caches.
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If the cookie is intended for use by a single user, the Set-Cookie2
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header SHOULD NOT be cached. A Set-Cookie2 header that is intended
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to be shared by multiple users MAY be cached.
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The origin server SHOULD send the following additional HTTP/1.1
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response headers, depending on circumstances:
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* To suppress caching of the Set-Cookie2 header:
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Cache-control: no-cache="set-cookie2"
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and one of the following:
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* To suppress caching of a private document in shared caches:
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Cache-control: private
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Kristol & Montulli Standards Track [Page 7]
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RFC 2965 HTTP State Management Mechanism October 2000
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* To allow caching of a document and require that it be validated
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before returning it to the client:
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Cache-Control: must-revalidate, max-age=0
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* To allow caching of a document, but to require that proxy
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caches (not user agent caches) validate it before returning it
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to the client:
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Cache-Control: proxy-revalidate, max-age=0
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* To allow caching of a document and request that it be validated
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before returning it to the client (by "pre-expiring" it):
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Cache-control: max-age=0
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Not all caches will revalidate the document in every case.
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HTTP/1.1 servers MUST send Expires: old-date (where old-date is a
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date long in the past) on responses containing Set-Cookie2 response
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headers unless they know for certain (by out of band means) that
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there are no HTTP/1.0 proxies in the response chain. HTTP/1.1
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servers MAY send other Cache-Control directives that permit caching
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by HTTP/1.1 proxies in addition to the Expires: old-date directive;
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the Cache-Control directive will override the Expires: old-date for
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HTTP/1.1 proxies.
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3.3 User Agent Role
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3.3.1 Interpreting Set-Cookie2 The user agent keeps separate track
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of state information that arrives via Set-Cookie2 response headers
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from each origin server (as distinguished by name or IP address and
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port). The user agent MUST ignore attribute-value pairs whose
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attribute it does not recognize. The user agent applies these
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defaults for optional attributes that are missing:
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Discard The default behavior is dictated by the presence or absence
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of a Max-Age attribute.
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Domain Defaults to the effective request-host. (Note that because
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there is no dot at the beginning of effective request-host,
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the default Domain can only domain-match itself.)
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Max-Age The default behavior is to discard the cookie when the user
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agent exits.
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Path Defaults to the path of the request URL that generated the
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Set-Cookie2 response, up to and including the right-most /.
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Kristol & Montulli Standards Track [Page 8]
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RFC 2965 HTTP State Management Mechanism October 2000
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Port The default behavior is that a cookie MAY be returned to any
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request-port.
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Secure If absent, the user agent MAY send the cookie over an
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insecure channel.
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3.3.2 Rejecting Cookies To prevent possible security or privacy
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violations, a user agent rejects a cookie according to rules below.
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The goal of the rules is to try to limit the set of servers for which
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a cookie is valid, based on the values of the Path, Domain, and Port
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attributes and the request-URI, request-host and request-port.
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A user agent rejects (SHALL NOT store its information) if the Version
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attribute is missing. Moreover, a user agent rejects (SHALL NOT
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store its information) if any of the following is true of the
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attributes explicitly present in the Set-Cookie2 response header:
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* The value for the Path attribute is not a prefix of the
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request-URI.
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* The value for the Domain attribute contains no embedded dots,
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and the value is not .local.
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* The effective host name that derives from the request-host does
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not domain-match the Domain attribute.
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* The request-host is a HDN (not IP address) and has the form HD,
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where D is the value of the Domain attribute, and H is a string
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that contains one or more dots.
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* The Port attribute has a "port-list", and the request-port was
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not in the list.
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Examples:
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* A Set-Cookie2 from request-host y.x.foo.com for Domain=.foo.com
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would be rejected, because H is y.x and contains a dot.
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* A Set-Cookie2 from request-host x.foo.com for Domain=.foo.com
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would be accepted.
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* A Set-Cookie2 with Domain=.com or Domain=.com., will always be
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rejected, because there is no embedded dot.
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* A Set-Cookie2 with Domain=ajax.com will be accepted, and the
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value for Domain will be taken to be .ajax.com, because a dot
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gets prepended to the value.
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Kristol & Montulli Standards Track [Page 9]
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RFC 2965 HTTP State Management Mechanism October 2000
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* A Set-Cookie2 with Port="80,8000" will be accepted if the
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request was made to port 80 or 8000 and will be rejected
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otherwise.
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* A Set-Cookie2 from request-host example for Domain=.local will
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be accepted, because the effective host name for the request-
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host is example.local, and example.local domain-matches .local.
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3.3.3 Cookie Management If a user agent receives a Set-Cookie2
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response header whose NAME is the same as that of a cookie it has
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previously stored, the new cookie supersedes the old when: the old
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and new Domain attribute values compare equal, using a case-
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insensitive string-compare; and, the old and new Path attribute
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values string-compare equal (case-sensitive). However, if the Set-
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Cookie2 has a value for Max-Age of zero, the (old and new) cookie is
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discarded. Otherwise a cookie persists (resources permitting) until
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whichever happens first, then gets discarded: its Max-Age lifetime is
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exceeded; or, if the Discard attribute is set, the user agent
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terminates the session.
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Because user agents have finite space in which to store cookies, they
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MAY also discard older cookies to make space for newer ones, using,
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for example, a least-recently-used algorithm, along with constraints
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on the maximum number of cookies that each origin server may set.
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If a Set-Cookie2 response header includes a Comment attribute, the
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user agent SHOULD store that information in a human-readable form
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with the cookie and SHOULD display the comment text as part of a
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cookie inspection user interface.
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If a Set-Cookie2 response header includes a CommentURL attribute, the
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user agent SHOULD store that information in a human-readable form
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with the cookie, or, preferably, SHOULD allow the user to follow the
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http_URL link as part of a cookie inspection user interface.
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The cookie inspection user interface may include a facility whereby a
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user can decide, at the time the user agent receives the Set-Cookie2
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response header, whether or not to accept the cookie. A potentially
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confusing situation could arise if the following sequence occurs:
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* the user agent receives a cookie that contains a CommentURL
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attribute;
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* the user agent's cookie inspection interface is configured so
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that it presents a dialog to the user before the user agent
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accepts the cookie;
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Kristol & Montulli Standards Track [Page 10]
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RFC 2965 HTTP State Management Mechanism October 2000
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* the dialog allows the user to follow the CommentURL link when
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the user agent receives the cookie; and,
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* when the user follows the CommentURL link, the origin server
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(or another server, via other links in the returned content)
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returns another cookie.
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The user agent SHOULD NOT send any cookies in this context. The user
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agent MAY discard any cookie it receives in this context that the
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user has not, through some user agent mechanism, deemed acceptable.
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User agents SHOULD allow the user to control cookie destruction, but
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they MUST NOT extend the cookie's lifetime beyond that controlled by
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the Discard and Max-Age attributes. An infrequently-used cookie may
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function as a "preferences file" for network applications, and a user
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may wish to keep it even if it is the least-recently-used cookie. One
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possible implementation would be an interface that allows the
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permanent storage of a cookie through a checkbox (or, conversely, its
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immediate destruction).
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Privacy considerations dictate that the user have considerable
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control over cookie management. The PRIVACY section contains more
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information.
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3.3.4 Sending Cookies to the Origin Server When it sends a request
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to an origin server, the user agent includes a Cookie request header
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if it has stored cookies that are applicable to the request, based on
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* the request-host and request-port;
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* the request-URI;
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* the cookie's age.
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The syntax for the header is:
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cookie = "Cookie:" cookie-version 1*((";" | ",") cookie-value)
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cookie-value = NAME "=" VALUE [";" path] [";" domain] [";" port]
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cookie-version = "$Version" "=" value
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NAME = attr
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VALUE = value
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path = "$Path" "=" value
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domain = "$Domain" "=" value
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port = "$Port" [ "=" <"> value <"> ]
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The value of the cookie-version attribute MUST be the value from the
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Version attribute of the corresponding Set-Cookie2 response header.
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Otherwise the value for cookie-version is 0. The value for the path
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RFC 2965 HTTP State Management Mechanism October 2000
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attribute MUST be the value from the Path attribute, if one was
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present, of the corresponding Set-Cookie2 response header. Otherwise
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the attribute SHOULD be omitted from the Cookie request header. The
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value for the domain attribute MUST be the value from the Domain
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attribute, if one was present, of the corresponding Set-Cookie2
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response header. Otherwise the attribute SHOULD be omitted from the
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Cookie request header.
630
631
The port attribute of the Cookie request header MUST mirror the Port
632
attribute, if one was present, in the corresponding Set-Cookie2
633
response header. That is, the port attribute MUST be present if the
634
Port attribute was present in the Set-Cookie2 header, and it MUST
635
have the same value, if any. Otherwise, if the Port attribute was
636
absent from the Set-Cookie2 header, the attribute likewise MUST be
637
omitted from the Cookie request header.
638
639
Note that there is neither a Comment nor a CommentURL attribute in
640
the Cookie request header corresponding to the ones in the Set-
641
Cookie2 response header. The user agent does not return the comment
642
information to the origin server.
643
644
The user agent applies the following rules to choose applicable
645
cookie-values to send in Cookie request headers from among all the
646
cookies it has received.
647
648
Domain Selection
649
The origin server's effective host name MUST domain-match the
650
Domain attribute of the cookie.
651
652
Port Selection
653
There are three possible behaviors, depending on the Port
654
attribute in the Set-Cookie2 response header:
655
656
1. By default (no Port attribute), the cookie MAY be sent to any
657
port.
658
659
2. If the attribute is present but has no value (e.g., Port), the
660
cookie MUST only be sent to the request-port it was received
661
from.
662
663
3. If the attribute has a port-list, the cookie MUST only be
664
returned if the new request-port is one of those listed in
665
port-list.
666
667
Path Selection
668
The request-URI MUST path-match the Path attribute of the cookie.
669
670
671
672
673
674
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RFC 2965 HTTP State Management Mechanism October 2000
677
678
679
Max-Age Selection
680
Cookies that have expired should have been discarded and thus are
681
not forwarded to an origin server.
682
683
If multiple cookies satisfy the criteria above, they are ordered in
684
the Cookie header such that those with more specific Path attributes
685
precede those with less specific. Ordering with respect to other
686
attributes (e.g., Domain) is unspecified.
687
688
Note: For backward compatibility, the separator in the Cookie header
689
is semi-colon (;) everywhere. A server SHOULD also accept comma (,)
690
as the separator between cookie-values for future compatibility.
691
692
3.3.5 Identifying What Version is Understood: Cookie2 The Cookie2
693
request header facilitates interoperation between clients and servers
694
that understand different versions of the cookie specification. When
695
the client sends one or more cookies to an origin server, if at least
696
one of those cookies contains a $Version attribute whose value is
697
different from the version that the client understands, then the
698
client MUST also send a Cookie2 request header, the syntax for which
699
is
700
701
cookie2 = "Cookie2:" cookie-version
702
703
Here the value for cookie-version is the highest version of cookie
704
specification (currently 1) that the client understands. The client
705
needs to send at most one such request header per request.
706
707
3.3.6 Sending Cookies in Unverifiable Transactions Users MUST have
708
control over sessions in order to ensure privacy. (See PRIVACY
709
section below.) To simplify implementation and to prevent an
710
additional layer of complexity where adequate safeguards exist,
711
however, this document distinguishes between transactions that are
712
verifiable and those that are unverifiable. A transaction is
713
verifiable if the user, or a user-designated agent, has the option to
714
review the request-URI prior to its use in the transaction. A
715
transaction is unverifiable if the user does not have that option.
716
Unverifiable transactions typically arise when a user agent
717
automatically requests inlined or embedded entities or when it
718
resolves redirection (3xx) responses from an origin server.
719
Typically the origin transaction, the transaction that the user
720
initiates, is verifiable, and that transaction may directly or
721
indirectly induce the user agent to make unverifiable transactions.
722
723
An unverifiable transaction is to a third-party host if its request-
724
host U does not domain-match the reach R of the request-host O in the
725
origin transaction.
726
727
728
729
730
Kristol & Montulli Standards Track [Page 13]
731
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RFC 2965 HTTP State Management Mechanism October 2000
733
734
735
When it makes an unverifiable transaction, a user agent MUST disable
736
all cookie processing (i.e., MUST NOT send cookies, and MUST NOT
737
accept any received cookies) if the transaction is to a third-party
738
host.
739
740
This restriction prevents a malicious service author from using
741
unverifiable transactions to induce a user agent to start or continue
742
a session with a server in a different domain. The starting or
743
continuation of such sessions could be contrary to the privacy
744
expectations of the user, and could also be a security problem.
745
746
User agents MAY offer configurable options that allow the user agent,
747
or any autonomous programs that the user agent executes, to ignore
748
the above rule, so long as these override options default to "off".
749
750
(N.B. Mechanisms may be proposed that will automate overriding the
751
third-party restrictions under controlled conditions.)
752
753
Many current user agents already provide a review option that would
754
render many links verifiable. For instance, some user agents display
755
the URL that would be referenced for a particular link when the mouse
756
pointer is placed over that link. The user can therefore determine
757
whether to visit that site before causing the browser to do so.
758
(Though not implemented on current user agents, a similar technique
759
could be used for a button used to submit a form -- the user agent
760
could display the action to be taken if the user were to select that
761
button.) However, even this would not make all links verifiable; for
762
example, links to automatically loaded images would not normally be
763
subject to "mouse pointer" verification.
764
765
Many user agents also provide the option for a user to view the HTML
766
source of a document, or to save the source to an external file where
767
it can be viewed by another application. While such an option does
768
provide a crude review mechanism, some users might not consider it
769
acceptable for this purpose.
770
771
3.4 How an Origin Server Interprets the Cookie Header
772
773
A user agent returns much of the information in the Set-Cookie2
774
header to the origin server when the request-URI path-matches the
775
Path attribute of the cookie. When it receives a Cookie header, the
776
origin server SHOULD treat cookies with NAMEs whose prefix is $
777
specially, as an attribute for the cookie.
778
779
780
781
782
783
784
785
786
Kristol & Montulli Standards Track [Page 14]
787
788
RFC 2965 HTTP State Management Mechanism October 2000
789
790
791
3.5 Caching Proxy Role
792
793
One reason for separating state information from both a URL and
794
document content is to facilitate the scaling that caching permits.
795
To support cookies, a caching proxy MUST obey these rules already in
796
the HTTP specification:
797
798
* Honor requests from the cache, if possible, based on cache
799
validity rules.
800
801
* Pass along a Cookie request header in any request that the
802
proxy must make of another server.
803
804
* Return the response to the client. Include any Set-Cookie2
805
response header.
806
807
* Cache the received response subject to the control of the usual
808
headers, such as Expires,
809
810
Cache-control: no-cache
811
812
and
813
814
Cache-control: private
815
816
* Cache the Set-Cookie2 subject to the control of the usual
817
header,
818
819
Cache-control: no-cache="set-cookie2"
820
821
(The Set-Cookie2 header should usually not be cached.)
822
823
Proxies MUST NOT introduce Set-Cookie2 (Cookie) headers of their own
824
in proxy responses (requests).
825
826
4. EXAMPLES
827
828
4.1 Example 1
829
830
Most detail of request and response headers has been omitted. Assume
831
the user agent has no stored cookies.
832
833
1. User Agent -> Server
834
835
POST /acme/login HTTP/1.1
836
[form data]
837
838
User identifies self via a form.
839
840
841
842
Kristol & Montulli Standards Track [Page 15]
843
844
RFC 2965 HTTP State Management Mechanism October 2000
845
846
847
2. Server -> User Agent
848
849
HTTP/1.1 200 OK
850
Set-Cookie2: Customer="WILE_E_COYOTE"; Version="1"; Path="/acme"
851
852
Cookie reflects user's identity.
853
854
3. User Agent -> Server
855
856
POST /acme/pickitem HTTP/1.1
857
Cookie: $Version="1"; Customer="WILE_E_COYOTE"; $Path="/acme"
858
[form data]
859
860
User selects an item for "shopping basket".
861
862
4. Server -> User Agent
863
864
HTTP/1.1 200 OK
865
Set-Cookie2: Part_Number="Rocket_Launcher_0001"; Version="1";
866
Path="/acme"
867
868
Shopping basket contains an item.
869
870
5. User Agent -> Server
871
872
POST /acme/shipping HTTP/1.1
873
Cookie: $Version="1";
874
Customer="WILE_E_COYOTE"; $Path="/acme";
875
Part_Number="Rocket_Launcher_0001"; $Path="/acme"
876
[form data]
877
878
User selects shipping method from form.
879
880
6. Server -> User Agent
881
882
HTTP/1.1 200 OK
883
Set-Cookie2: Shipping="FedEx"; Version="1"; Path="/acme"
884
885
New cookie reflects shipping method.
886
887
7. User Agent -> Server
888
889
POST /acme/process HTTP/1.1
890
Cookie: $Version="1";
891
Customer="WILE_E_COYOTE"; $Path="/acme";
892
Part_Number="Rocket_Launcher_0001"; $Path="/acme";
893
Shipping="FedEx"; $Path="/acme"
894
[form data]
895
896
897
898
Kristol & Montulli Standards Track [Page 16]
899
900
RFC 2965 HTTP State Management Mechanism October 2000
901
902
903
User chooses to process order.
904
905
8. Server -> User Agent
906
907
HTTP/1.1 200 OK
908
909
Transaction is complete.
910
911
The user agent makes a series of requests on the origin server, after
912
each of which it receives a new cookie. All the cookies have the
913
same Path attribute and (default) domain. Because the request-URIs
914
all path-match /acme, the Path attribute of each cookie, each request
915
contains all the cookies received so far.
916
917
4.2 Example 2
918
919
This example illustrates the effect of the Path attribute. All
920
detail of request and response headers has been omitted. Assume the
921
user agent has no stored cookies.
922
923
Imagine the user agent has received, in response to earlier requests,
924
the response headers
925
926
Set-Cookie2: Part_Number="Rocket_Launcher_0001"; Version="1";
927
Path="/acme"
928
929
and
930
931
Set-Cookie2: Part_Number="Riding_Rocket_0023"; Version="1";
932
Path="/acme/ammo"
933
934
A subsequent request by the user agent to the (same) server for URLs
935
of the form /acme/ammo/... would include the following request
936
header:
937
938
Cookie: $Version="1";
939
Part_Number="Riding_Rocket_0023"; $Path="/acme/ammo";
940
Part_Number="Rocket_Launcher_0001"; $Path="/acme"
941
942
Note that the NAME=VALUE pair for the cookie with the more specific
943
Path attribute, /acme/ammo, comes before the one with the less
944
specific Path attribute, /acme. Further note that the same cookie
945
name appears more than once.
946
947
A subsequent request by the user agent to the (same) server for a URL
948
of the form /acme/parts/ would include the following request header:
949
950
951
952
953
954
Kristol & Montulli Standards Track [Page 17]
955
956
RFC 2965 HTTP State Management Mechanism October 2000
957
958
959
Cookie: $Version="1"; Part_Number="Rocket_Launcher_0001";
960
$Path="/acme"
961
962
Here, the second cookie's Path attribute /acme/ammo is not a prefix
963
of the request URL, /acme/parts/, so the cookie does not get
964
forwarded to the server.
965
966
5. IMPLEMENTATION CONSIDERATIONS
967
968
Here we provide guidance on likely or desirable details for an origin
969
server that implements state management.
970
971
5.1 Set-Cookie2 Content
972
973
An origin server's content should probably be divided into disjoint
974
application areas, some of which require the use of state
975
information. The application areas can be distinguished by their
976
request URLs. The Set-Cookie2 header can incorporate information
977
about the application areas by setting the Path attribute for each
978
one.
979
980
The session information can obviously be clear or encoded text that
981
describes state. However, if it grows too large, it can become
982
unwieldy. Therefore, an implementor might choose for the session
983
information to be a key to a server-side resource. Of course, using
984
a database creates some problems that this state management
985
specification was meant to avoid, namely:
986
987
1. keeping real state on the server side;
988
989
2. how and when to garbage-collect the database entry, in case the
990
user agent terminates the session by, for example, exiting.
991
992
5.2 Stateless Pages
993
994
Caching benefits the scalability of WWW. Therefore it is important
995
to reduce the number of documents that have state embedded in them
996
inherently. For example, if a shopping-basket-style application
997
always displays a user's current basket contents on each page, those
998
pages cannot be cached, because each user's basket's contents would
999
be different. On the other hand, if each page contains just a link
1000
that allows the user to "Look at My Shopping Basket", the page can be
1001
cached.
1002
1003
1004
1005
1006
1007
1008
1009
1010
Kristol & Montulli Standards Track [Page 18]
1011
1012
RFC 2965 HTTP State Management Mechanism October 2000
1013
1014
1015
5.3 Implementation Limits
1016
1017
Practical user agent implementations have limits on the number and
1018
size of cookies that they can store. In general, user agents' cookie
1019
support should have no fixed limits. They should strive to store as
1020
many frequently-used cookies as possible. Furthermore, general-use
1021
user agents SHOULD provide each of the following minimum capabilities
1022
individually, although not necessarily simultaneously:
1023
1024
* at least 300 cookies
1025
1026
* at least 4096 bytes per cookie (as measured by the characters
1027
that comprise the cookie non-terminal in the syntax description
1028
of the Set-Cookie2 header, and as received in the Set-Cookie2
1029
header)
1030
1031
* at least 20 cookies per unique host or domain name
1032
1033
User agents created for specific purposes or for limited-capacity
1034
devices SHOULD provide at least 20 cookies of 4096 bytes, to ensure
1035
that the user can interact with a session-based origin server.
1036
1037
The information in a Set-Cookie2 response header MUST be retained in
1038
its entirety. If for some reason there is inadequate space to store
1039
the cookie, it MUST be discarded, not truncated.
1040
1041
Applications should use as few and as small cookies as possible, and
1042
they should cope gracefully with the loss of a cookie.
1043
1044
5.3.1 Denial of Service Attacks User agents MAY choose to set an
1045
upper bound on the number of cookies to be stored from a given host
1046
or domain name or on the size of the cookie information. Otherwise a
1047
malicious server could attempt to flood a user agent with many
1048
cookies, or large cookies, on successive responses, which would force
1049
out cookies the user agent had received from other servers. However,
1050
the minima specified above SHOULD still be supported.
1051
1052
6. PRIVACY
1053
1054
Informed consent should guide the design of systems that use cookies.
1055
A user should be able to find out how a web site plans to use
1056
information in a cookie and should be able to choose whether or not
1057
those policies are acceptable. Both the user agent and the origin
1058
server must assist informed consent.
1059
1060
1061
1062
1063
1064
1065
1066
Kristol & Montulli Standards Track [Page 19]
1067
1068
RFC 2965 HTTP State Management Mechanism October 2000
1069
1070
1071
6.1 User Agent Control
1072
1073
An origin server could create a Set-Cookie2 header to track the path
1074
of a user through the server. Users may object to this behavior as
1075
an intrusive accumulation of information, even if their identity is
1076
not evident. (Identity might become evident, for example, if a user
1077
subsequently fills out a form that contains identifying information.)
1078
This state management specification therefore requires that a user
1079
agent give the user control over such a possible intrusion, although
1080
the interface through which the user is given this control is left
1081
unspecified. However, the control mechanisms provided SHALL at least
1082
allow the user
1083
1084
* to completely disable the sending and saving of cookies.
1085
1086
* to determine whether a stateful session is in progress.
1087
1088
* to control the saving of a cookie on the basis of the cookie's
1089
Domain attribute.
1090
1091
Such control could be provided, for example, by mechanisms
1092
1093
* to notify the user when the user agent is about to send a
1094
cookie to the origin server, to offer the option not to begin a
1095
session.
1096
1097
* to display a visual indication that a stateful session is in
1098
progress.
1099
1100
* to let the user decide which cookies, if any, should be saved
1101
when the user concludes a window or user agent session.
1102
1103
* to let the user examine and delete the contents of a cookie at
1104
any time.
1105
1106
A user agent usually begins execution with no remembered state
1107
information. It SHOULD be possible to configure a user agent never
1108
to send Cookie headers, in which case it can never sustain state with
1109
an origin server. (The user agent would then behave like one that is
1110
unaware of how to handle Set-Cookie2 response headers.)
1111
1112
When the user agent terminates execution, it SHOULD let the user
1113
discard all state information. Alternatively, the user agent MAY ask
1114
the user whether state information should be retained; the default
1115
should be "no". If the user chooses to retain state information, it
1116
would be restored the next time the user agent runs.
1117
1118
1119
1120
1121
1122
Kristol & Montulli Standards Track [Page 20]
1123
1124
RFC 2965 HTTP State Management Mechanism October 2000
1125
1126
1127
NOTE: User agents should probably be cautious about using files to
1128
store cookies long-term. If a user runs more than one instance of
1129
the user agent, the cookies could be commingled or otherwise
1130
corrupted.
1131
1132
6.2 Origin Server Role
1133
1134
An origin server SHOULD promote informed consent by adding CommentURL
1135
or Comment information to the cookies it sends. CommentURL is
1136
preferred because of the opportunity to provide richer information in
1137
a multiplicity of languages.
1138
1139
6.3 Clear Text
1140
1141
The information in the Set-Cookie2 and Cookie headers is unprotected.
1142
As a consequence:
1143
1144
1. Any sensitive information that is conveyed in them is exposed
1145
to intruders.
1146
1147
2. A malicious intermediary could alter the headers as they travel
1148
in either direction, with unpredictable results.
1149
1150
These facts imply that information of a personal and/or financial
1151
nature should only be sent over a secure channel. For less sensitive
1152
information, or when the content of the header is a database key, an
1153
origin server should be vigilant to prevent a bad Cookie value from
1154
causing failures.
1155
1156
A user agent in a shared user environment poses a further risk.
1157
Using a cookie inspection interface, User B could examine the
1158
contents of cookies that were saved when User A used the machine.
1159
1160
7. SECURITY CONSIDERATIONS
1161
1162
7.1 Protocol Design
1163
1164
The restrictions on the value of the Domain attribute, and the rules
1165
concerning unverifiable transactions, are meant to reduce the ways
1166
that cookies can "leak" to the "wrong" site. The intent is to
1167
restrict cookies to one host, or a closely related set of hosts.
1168
Therefore a request-host is limited as to what values it can set for
1169
Domain. We consider it acceptable for hosts host1.foo.com and
1170
host2.foo.com to share cookies, but not a.com and b.com.
1171
1172
Similarly, a server can set a Path only for cookies that are related
1173
to the request-URI.
1174
1175
1176
1177
1178
Kristol & Montulli Standards Track [Page 21]
1179
1180
RFC 2965 HTTP State Management Mechanism October 2000
1181
1182
1183
7.2 Cookie Spoofing
1184
1185
Proper application design can avoid spoofing attacks from related
1186
domains. Consider:
1187
1188
1. User agent makes request to victim.cracker.edu, gets back
1189
cookie session_id="1234" and sets the default domain
1190
victim.cracker.edu.
1191
1192
2. User agent makes request to spoof.cracker.edu, gets back cookie
1193
session-id="1111", with Domain=".cracker.edu".
1194
1195
3. User agent makes request to victim.cracker.edu again, and
1196
passes
1197
1198
Cookie: $Version="1"; session_id="1234",
1199
$Version="1"; session_id="1111"; $Domain=".cracker.edu"
1200
1201
The server at victim.cracker.edu should detect that the second
1202
cookie was not one it originated by noticing that the Domain
1203
attribute is not for itself and ignore it.
1204
1205
7.3 Unexpected Cookie Sharing
1206
1207
A user agent SHOULD make every attempt to prevent the sharing of
1208
session information between hosts that are in different domains.
1209
Embedded or inlined objects may cause particularly severe privacy
1210
problems if they can be used to share cookies between disparate
1211
hosts. For example, a malicious server could embed cookie
1212
information for host a.com in a URI for a CGI on host b.com. User
1213
agent implementors are strongly encouraged to prevent this sort of
1214
exchange whenever possible.
1215
1216
7.4 Cookies For Account Information
1217
1218
While it is common practice to use them this way, cookies are not
1219
designed or intended to be used to hold authentication information,
1220
such as account names and passwords. Unless such cookies are
1221
exchanged over an encrypted path, the account information they
1222
contain is highly vulnerable to perusal and theft.
1223
1224
8. OTHER, SIMILAR, PROPOSALS
1225
1226
Apart from RFC 2109, three other proposals have been made to
1227
accomplish similar goals. This specification began as an amalgam of
1228
Kristol's State-Info proposal [DMK95] and Netscape's Cookie proposal
1229
[Netscape].
1230
1231
1232
1233
1234
Kristol & Montulli Standards Track [Page 22]
1235
1236
RFC 2965 HTTP State Management Mechanism October 2000
1237
1238
1239
Brian Behlendorf proposed a Session-ID header that would be user-
1240
agent-initiated and could be used by an origin server to track
1241
"clicktrails". It would not carry any origin-server-defined state,
1242
however. Phillip Hallam-Baker has proposed another client-defined
1243
session ID mechanism for similar purposes.
1244
1245
While both session IDs and cookies can provide a way to sustain
1246
stateful sessions, their intended purpose is different, and,
1247
consequently, the privacy requirements for them are different. A
1248
user initiates session IDs to allow servers to track progress through
1249
them, or to distinguish multiple users on a shared machine. Cookies
1250
are server-initiated, so the cookie mechanism described here gives
1251
users control over something that would otherwise take place without
1252
the users' awareness. Furthermore, cookies convey rich, server-
1253
selected information, whereas session IDs comprise user-selected,
1254
simple information.
1255
1256
9. HISTORICAL
1257
1258
9.1 Compatibility with Existing Implementations
1259
1260
Existing cookie implementations, based on the Netscape specification,
1261
use the Set-Cookie (not Set-Cookie2) header. User agents that
1262
receive in the same response both a Set-Cookie and Set-Cookie2
1263
response header for the same cookie MUST discard the Set-Cookie
1264
information and use only the Set-Cookie2 information. Furthermore, a
1265
user agent MUST assume, if it received a Set-Cookie2 response header,
1266
that the sending server complies with this document and will
1267
understand Cookie request headers that also follow this
1268
specification.
1269
1270
New cookies MUST replace both equivalent old- and new-style cookies.
1271
That is, if a user agent that follows both this specification and
1272
Netscape's original specification receives a Set-Cookie2 response
1273
header, and the NAME and the Domain and Path attributes match (per
1274
the Cookie Management section) a Netscape-style cookie, the
1275
Netscape-style cookie MUST be discarded, and the user agent MUST
1276
retain only the cookie adhering to this specification.
1277
1278
Older user agents that do not understand this specification, but that
1279
do understand Netscape's original specification, will not recognize
1280
the Set-Cookie2 response header and will receive and send cookies
1281
according to the older specification.
1282
1283
1284
1285
1286
1287
1288
1289
1290
Kristol & Montulli Standards Track [Page 23]
1291
1292
RFC 2965 HTTP State Management Mechanism October 2000
1293
1294
1295
A user agent that supports both this specification and Netscape-style
1296
cookies SHOULD send a Cookie request header that follows the older
1297
Netscape specification if it received the cookie in a Set-Cookie
1298
response header and not in a Set-Cookie2 response header. However,
1299
it SHOULD send the following request header as well:
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Cookie2: $Version="1"
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The Cookie2 header advises the server that the user agent understands
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new-style cookies. If the server understands new-style cookies, as
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well, it SHOULD continue the stateful session by sending a Set-
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Cookie2 response header, rather than Set-Cookie. A server that does
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not understand new-style cookies will simply ignore the Cookie2
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request header.
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9.2 Caching and HTTP/1.0
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Some caches, such as those conforming to HTTP/1.0, will inevitably
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cache the Set-Cookie2 and Set-Cookie headers, because there was no
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mechanism to suppress caching of headers prior to HTTP/1.1. This
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caching can lead to security problems. Documents transmitted by an
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origin server along with Set-Cookie2 and Set-Cookie headers usually
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either will be uncachable, or will be "pre-expired". As long as
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caches obey instructions not to cache documents (following Expires:
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<a date in the past> or Pragma: no-cache (HTTP/1.0), or Cache-
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control: no-cache (HTTP/1.1)) uncachable documents present no
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problem. However, pre-expired documents may be stored in caches.
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They require validation (a conditional GET) on each new request, but
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some cache operators loosen the rules for their caches, and sometimes
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serve expired documents without first validating them. This
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combination of factors can lead to cookies meant for one user later
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being sent to another user. The Set-Cookie2 and Set-Cookie headers
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are stored in the cache, and, although the document is stale
1328
(expired), the cache returns the document in response to later
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requests, including cached headers.
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10. ACKNOWLEDGEMENTS
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This document really represents the collective efforts of the HTTP
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Working Group of the IETF and, particularly, the following people, in
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addition to the authors: Roy Fielding, Yaron Goland, Marc Hedlund,
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Ted Hardie, Koen Holtman, Shel Kaphan, Rohit Khare, Foteos Macrides,
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David W. Morris.
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Kristol & Montulli Standards Track [Page 24]
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RFC 2965 HTTP State Management Mechanism October 2000
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11. AUTHORS' ADDRESSES
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David M. Kristol
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Bell Laboratories, Lucent Technologies
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600 Mountain Ave. Room 2A-333
1356
Murray Hill, NJ 07974
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Phone: (908) 582-2250
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Fax: (908) 582-1239
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EMail: dmk@bell-labs.com
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Lou Montulli
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Epinions.com, Inc.
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2037 Landings Dr.
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Mountain View, CA 94301
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EMail: lou@montulli.org
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12. REFERENCES
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[DMK95] Kristol, D.M., "Proposed HTTP State-Info Mechanism",
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available at <http://portal.research.bell-
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labs.com/~dmk/state-info.html>, September, 1995.
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[Netscape] "Persistent Client State -- HTTP Cookies", available at
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<http://www.netscape.com/newsref/std/cookie_spec.html>,
1378
undated.
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[RFC2109] Kristol, D. and L. Montulli, "HTTP State Management
1381
Mechanism", RFC 2109, February 1997.
1382
1383
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
1384
Requirement Levels", BCP 14, RFC 2119, March 1997.
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1386
[RFC2279] Yergeau, F., "UTF-8, a transformation format of Unicode
1387
and ISO-10646", RFC 2279, January 1998.
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1389
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
1390
Resource Identifiers (URI): Generic Syntax", RFC 2396,
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August 1998.
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[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T.
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Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
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RFC 2616, June 1999.
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Kristol & Montulli Standards Track [Page 25]
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RFC 2965 HTTP State Management Mechanism October 2000
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13. Full Copyright Statement
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Copyright (C) The Internet Society (2000). All Rights Reserved.
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This document and translations of it may be copied and furnished to
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others, and derivative works that comment on or otherwise explain it
1413
or assist in its implementation may be prepared, copied, published
1414
and distributed, in whole or in part, without restriction of any
1415
kind, provided that the above copyright notice and this paragraph are
1416
included on all such copies and derivative works. However, this
1417
document itself may not be modified in any way, such as by removing
1418
the copyright notice or references to the Internet Society or other
1419
Internet organizations, except as needed for the purpose of
1420
developing Internet standards in which case the procedures for
1421
copyrights defined in the Internet Standards process must be
1422
followed, or as required to translate it into languages other than
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English.
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The limited permissions granted above are perpetual and will not be
1426
revoked by the Internet Society or its successors or assigns.
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1428
This document and the information contained herein is provided on an
1429
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
1430
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
1431
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
1432
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
1433
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Acknowledgement
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Funding for the RFC Editor function is currently provided by the
1438
Internet Society.
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Kristol & Montulli Standards Track [Page 26]
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Loggerhead is a web-based interface for Breezy
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