[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07

None (yet)                                                      A. Barth
Internet-Draft                                             U.C. Berkeley
Expires: February 22, 2010                               August 21, 2009


                    HTTP State Management Mechanism
                         draft-abarth-cookie-02

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may contain material
   from IETF Documents or IETF Contributions published or made publicly
   available before November 10, 2008.  The person(s) controlling the
   copyright in some of this material may not have granted the IETF
   Trust the right to allow modifications of such material outside the
   IETF Standards Process.  Without obtaining an adequate license from
   the person(s) controlling the copyright in such materials, this
   document may not be modified outside the IETF Standards Process, and
   derivative works of it may not be created outside the IETF Standards
   Process, except to format it for publication as an RFC or to
   translate it into languages other than English.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on February 22, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of



Barth                   Expires February 22, 2010               [Page 1]


Internet-Draft       HTTP State Management Mechanism         August 2009


   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.
















































Barth                   Expires February 22, 2010               [Page 2]


Internet-Draft       HTTP State Management Mechanism         August 2009


Abstract

   This document defines the HTTP Cookie and Set-Cookie headers.

      NOTE: Much of the text herein is completely wrong.  If you have
      suggestions for improving the draft, please send email to
      http-state@ietf.org.  Suggestions with test cases are especially
      appreciated.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Protocol Description . . . . . . . . . . . . . . . . . . . . .  7
     4.1.  Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . .  7
       4.1.1.  Syntax . . . . . . . . . . . . . . . . . . . . . . . .  7
       4.1.2.  Semantics  . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Cookie . . . . . . . . . . . . . . . . . . . . . . . . . .  9
       4.2.1.  Syntax . . . . . . . . . . . . . . . . . . . . . . . .  9
       4.2.2.  Semantics  . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Controlling Caching  . . . . . . . . . . . . . . . . . . . 10
   5.  User Agent Conformance . . . . . . . . . . . . . . . . . . . . 12
     5.1.  Parsing the Set-Cookie Header  . . . . . . . . . . . . . . 12
       5.1.1.  The Max-Age Attribute  . . . . . . . . . . . . . . . . 14
       5.1.2.  The Expires Attribute  . . . . . . . . . . . . . . . . 14
       5.1.3.  The Domain Attribute . . . . . . . . . . . . . . . . . 15
       5.1.4.  The Path Attribute . . . . . . . . . . . . . . . . . . 15
       5.1.5.  The Secure Attribute . . . . . . . . . . . . . . . . . 16
       5.1.6.  The HttpOnly Attribute . . . . . . . . . . . . . . . . 16
     5.2.  Storage Model  . . . . . . . . . . . . . . . . . . . . . . 16
     5.3.  The Cookie Header  . . . . . . . . . . . . . . . . . . . . 19
   6.  Implementation Considerations  . . . . . . . . . . . . . . . . 21
     6.1.  Set-Cookie Content . . . . . . . . . . . . . . . . . . . . 21
     6.2.  Implementation Limits  . . . . . . . . . . . . . . . . . . 21
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
     7.1.  Clear Text . . . . . . . . . . . . . . . . . . . . . . . . 22
     7.2.  Cookie Spoofing  . . . . . . . . . . . . . . . . . . . . . 22
   8.  Other, Similar, Proposals  . . . . . . . . . . . . . . . . . . 23
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 24
   Appendix B.  Tabled Items  . . . . . . . . . . . . . . . . . . . . 25
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 26







Barth                   Expires February 22, 2010               [Page 3]


Internet-Draft       HTTP State Management Mechanism         August 2009


1.  Introduction

   This document defines the HTTP Cookie and Set-Cookie header.
















































Barth                   Expires February 22, 2010               [Page 4]


Internet-Draft       HTTP State Management Mechanism         August 2009


2.  Terminology

   The terms user agent, client, server, proxy, and origin server have
   the same meaning as in the HTTP/1.0 specification.

   Fully-qualified host name (FQHN) means either the fully-qualified
   domain name (FQDN) of a host (i.e., a completely specified domain
   name ending in a top-level domain such as .com or .uk), or the
   numeric Internet Protocol (IP) address of a host.  The fully
   qualified domain name is preferred; use of numeric IP addresses is
   strongly discouraged.  [TODO: What does "strongly discouraged" mean?]

   The terms request-host and request-URI refer to the values the client
   would send to the server as, respectively, the host (but not port)
   and abs_path portions of the absoluteURI (http_URL) of the HTTP
   request line.  Note that request-host must be a FQHN.  Hosts names
   can be specified either as an IP address or a FQHN string.

   Because it was used in Netscape's original implementation of state
   management, we will use the term cookie to refer to the state
   information that passes between an origin server and user agent, and
   that gets stored by the user agent.





























Barth                   Expires February 22, 2010               [Page 5]


Internet-Draft       HTTP State Management Mechanism         August 2009


3.  Overview

   We outline here a way for an origin server to send state information
   to the user agent, and for the user agent to return the state
   information to the origin server.

   The origin server initiates a session, if it so desires, by including
   a Set-Cookie header in an HTTP response.  (Note that "session" here
   does not refer to a persistent network connection but to a logical
   session created from HTTP requests and responses.  The presence or
   absence of a persistent connection should have no effect on the use
   of cookie-derived sessions).

   A user agent returns a Cookie request header (see below) to the
   origin server if it chooses to continue a session.  The origin server
   may ignore it or use it to determine the current state of the
   session.  It may send the client a Set-Cookie response header with
   the same or different information, or it may send no Set-Cookie
   header at all.

   Servers may return a Set-Cookie response headers with any response.
   User agents should send Cookie request headers, subject to other
   rules detailed below, with every request.

   An origin server may include multiple Set-Cookie headers in a
   response.  Note that an intervening gateway MUST NOT fold multiple
   Set-Cookie headers into a single header.

   [TODO: Overview the Set-Cookie and Cookie headers.]

3.1.  Examples

   [TODO: Put some examples here.


















Barth                   Expires February 22, 2010               [Page 6]


Internet-Draft       HTTP State Management Mechanism         August 2009


4.  Protocol Description

   The cookie protocol consists of two HTTP headers: the Set-Cookie
   header and the Cookie header.  The server sends the Set-Cookie header
   is to the user agent in an HTTP response, causing the user agent to
   modify the Cookie header it returns to the server.

   This section describes the syntax and semantics of the protocol.
   Detailed conformance requirements for user agents are given in
   Section [TODO].

4.1.  Set-Cookie

4.1.1.  Syntax

   Informally, the Set-Cookie response header comprises the token Set-
   Cookie:, followed by a cookie.  Each cookie begins with a name-value-
   pair, followed by zero or more semi-colon-separated attribute-value
   pairs.


     set-cookie-header = "Set-Cookie:" name-value-pairs
     name-value-pairs  = name-value-pair *(";" name-value-pair)
     name-value-pair   = name ["=" value]        ; optional value
     name              = token
     value             = *CHAR


   The valid character for the value production vary depending on the
   attribute name.

   [TODO: Investigate what token actually means.]

   Attributes names are case-insensitive.  White space is permitted
   between tokens.  Servers MUST NOT include two attributes with the
   same name.  Note that although the above syntax description shows
   value as optional, some attributes require values.

   The cookie-value is opaque to the user agent and MAY be anything the
   origin server chooses to send, possibly in a server-selected
   printable ASCII encoding.  "Opaque" implies that the content is of
   interest and relevance only to the origin server.  The content may,
   in fact, be readable by anyone who examines the Set-Cookie header.

   NOTE: The syntax above allows whitespace between the attribute and
   the U+3D ("=") character.  Servers wishing to interoperate with some
   legacy user agents might wish to elide this extra white space to
   maximize compatibility.



Barth                   Expires February 22, 2010               [Page 7]


Internet-Draft       HTTP State Management Mechanism         August 2009


4.1.2.  Semantics

   When the user agent receives a Set-Cookie header, the user agent
   stores the cookie in its cookie store.  When the user agent makes
   another HTTP request to the origin server, the user agent returns the
   cookie in the Cookie header.

   The server can override the default handling of cookies by specifying
   cookie attributes.  User agents ignore unrecognized cookie
   attributes.

4.1.2.1.  Max-Age

   [TODO: Consider removing Max-Age from the server conformance section
   because it's not supported by IE.]

   Syntax  A sequence of ASCII numerals.

   Semantics  The value of the Max-Age attribute represents the maximum
      lifetime of the cookie, measured in seconds from the moment the
      user agent receives the cookie.  If the server does not supply an
      Expires or a Max-Age attribute, the lifetime of the cookie is
      limited to the current session (as defined by the user agent).

4.1.2.2.  Expires

   Syntax  An RFC 1123 date [cite].  (Note that user agents use very
      forgiving date parers; see Section [TODO]).

   Semantics  The value of the Expires attribute represents the maximum
      lifetime of the cookie, represented as the point in time at which
      the cookie expires.  If the server does not supply an Expires or a
      Max-Age attribute, the lifetime of the cookie is limited to the
      current session (as defined by the user agent).

4.1.2.3.  Domain

   [TODO: Test Domain.]  The Domain attribute specifies the domain for
   which the cookie is valid.  The leading dot isn't required.  If there
   is no Domain attribute, the default is to return the cookie only to
   the origin server.  [TODO: You can only set cookies for related
   domains.]

4.1.2.4.  Path







Barth                   Expires February 22, 2010               [Page 8]


Internet-Draft       HTTP State Management Mechanism         August 2009


   Syntax  A sequence of characters beginning with a "/" character.

   Semantics  The Path attribute specifies the scope of the cookie
      within a given FQDN.  The user agent will include a cookie in an
      HTTP request only if the Request-URI's path matches, or is a
      subdirectory of, the cookie's Path attribute (where the "/"
      character is interpreted as a directory separator).  The default
      value for the Path attribute is the directory of the Request-URI
      when the cookie was received.

4.1.2.5.  Secure

   Syntax  Servers MUST NOT include a value.

   Semantics  The user agent SHOULD protect the confidentiality of
      cookies with the Secure attribute by not transmitting Secure
      cookies over an "insecure" channel (where "insecure" is defined by
      the user agent).

4.1.2.6.  HttpOnly

   Syntax  Servers MUST NOT include a value.

   Semantics  The user agent SHOULD protect confidentiality of cookies
      with the HttpOnly attribute by including HttpOnly cookies only
      when generating cookie strings for use in HTTP requests.

4.2.  Cookie

4.2.1.  Syntax

   The user agent returns stored cookies to the origin server in the
   Cookie header.  The Cookie header shares a common syntax with the
   Set-Cookie header, but the semantics of the header differ
   dramatically.


     cookie-header     = "Cookie:" name-value-pairs
     name-value-pairs  = name-value-pair *(";" name-value-pair)
     name-value-pair   = name "=" value
     name              = token
     value             = *CHAR


   NOTE: If the server supplies a Set-Cookie header that does not
   conform to the grammar in Section [TODO], the user agent might not
   supply a Cookie header that conforms to the preceding grammar.




Barth                   Expires February 22, 2010               [Page 9]


Internet-Draft       HTTP State Management Mechanism         August 2009


4.2.2.  Semantics

   Each name-value-pair represents a cookie stored by the user agent.
   The cookie name is returned in as the name and the cookie value is
   returned as the value.

   The meaning of the cookies in the Cookie header is not defined by
   this document.  Servers are expected to imbue these cookies with
   server-specific semantics.

4.3.  Controlling Caching

   [TODO: Should we go into this much detail here?  This seems redundant
   with the HTTP specs.]

   An origin server must be cognizant of the effect of possible caching
   of both the returned resource and the Set-Cookie header.  Caching
   "public" documents is desirable.  For example, if the origin server
   wants to use a public document such as a "front door" page as a
   sentinel to indicate the beginning of a session for which a Set-
   Cookie response header must be generated, the page should be stored
   in caches "pre-expired" so that the origin server will see further
   requests.  "Private documents", for example those that contain
   information strictly private to a session, should not be cached in
   shared caches.

   If the cookie is intended for use by a single user, the Set-Cookie
   header should not be cached.  A Set-Cookie header that is intended to
   be shared by multiple users may be cached.

   The origin server should send the following additional HTTP/1.1
   response headers, depending on circumstances: [TODO: Is this good
   advice?]

   o  To suppress caching of the Set-Cookie header: Cache-control: no-
      cache="set-cookie".

   and one of the following:

   o  To suppress caching of a private document in shared caches: Cache-
      Control: private.

   o  To allow caching of a document and require that it be validated
      before returning it to the client: Cache-Control: must-revalidate.

   o  To allow caching of a document, but to require that proxy caches
      (not user agent caches) validate it before returning it to the
      client: Cache-Control: proxy-revalidate.



Barth                   Expires February 22, 2010              [Page 10]


Internet-Draft       HTTP State Management Mechanism         August 2009


   o  To allow caching of a document and request that it be validated
      before returning it to the client (by "pre-expiring" it): Cache-
      Control: max-age=0.  Not all caches will revalidate the document
      in every case.

   HTTP/1.1 servers must send Expires: old-date (where old-date is a
   date long in the past) on responses containing Set-Cookie response
   headers unless they know for certain (by out of band means) that
   there are no downstream HTTP/1.0 proxies.  HTTP/1.1 servers may send
   other Cache-Control directives that permit caching by HTTP/1.1
   proxies in addition to the Expires: old-date directive; the Cache-
   Control directive will override the Expires: old-date for HTTP/1.1
   proxies.






































Barth                   Expires February 22, 2010              [Page 11]


Internet-Draft       HTTP State Management Mechanism         August 2009


5.  User Agent Conformance

   Not all origin servers conform to the behavior specified in the
   previous section.  To ensure interoperability, user agents MUST
   process cookies in a manner that is "black-box" indistinguishable
   from the requirements in this section.

5.1.  Parsing the Set-Cookie Header

   Let an LWS character be either a U+20 (SPACE) or a U+09 (TAB)
   character.

   A user agent MUST use the following algorithm to parse the Set-Cookie
   header:

   1.  [TODO: Deal with "," characters.  My current thinking is that we
       don't actually have to do anything special for them.]

   2.  If the header contains a U+3B (";") character:

          the name-value-pair string is characters up to, but not
          including, the first U+3B (";"), and the unparsed-cookie-
          attributes are the remainder of the header (including the U+3B
          (";") in question).

       Otherwise:

          the name-value-pair string is all the character contained in
          the header, and the unparsed-cookie-attributes is the empty
          string.

   3.  If the name-value-pair string contains a U+3D ("=") character:

          the (possibly empty) name string is the characters up to, but
          not including, the first U+3D ("=") character, and the
          (possibly empty) value string is the characters after the
          first U+3D ("=") character.

       Otherwise:

          the name string is empty, and the value string is the entire
          name-value-pair string.

   4.  Remove any leading or trailing space from the name string and the
       value string.

   5.  The cookie-name is the name string, and the cookie-value is the
       value string.



Barth                   Expires February 22, 2010              [Page 12]


Internet-Draft       HTTP State Management Mechanism         August 2009


   The user agent MUST use the following algorithm to parse the
   unparsed-attributes:

   1.  If the unparsed-attributes string is empty, skip the rest of
       these steps.

   2.  Consume the first character of the unparsed-attributes (which
       will be a U+3B (";") character).

   3.  If the remaining unparsed-attributes contains a U+3B (";")
       character:

          Consume the characters of the unparsed-attributes up to, but
          not including, the first U+3B (";") character.

       Otherwise:

          Consume the remainder of the unparsed-attributes.

       The characters consumed in this step comprise the attribute-
       value-pair string.

   4.  If the attribute-value-pair string contains a U+3D ("=")
       character:

          the (possibly empty) name string is the characters up to, but
          not including, the first U+3D ("=") character, and the
          (possibly empty) value string is the characters after the
          first U+3D ("=") character .

       Otherwise:

          the name string is the entire attribute-value-pair string, and
          the value string is empty.  (Note that this step differs from
          the analogous step when parsing the name-value-pair string.)

   5.  Remove any leading or trailing space from the name string and the
       value string.

   6.  If the name is a ASCII case-insensitive match for an entry in the
       following table, process the value string as instructed.










Barth                   Expires February 22, 2010              [Page 13]


Internet-Draft       HTTP State Management Mechanism         August 2009


          Attribute  |  Instruction
         ------------+---------------------
          Max-Age    |  See Section [TODO]
          Expires    |  See Section [TODO]
          Domain     |  See Section [TODO]
          Path       |  See Section [TODO]
          Secure     |  See Section [TODO]
          HttpOnly   |  See Section [TODO]


   7.  Return to Step 1.

   [TODO: Can parsing a cookie ever fail?  Doesn't look like it!  Well,
   unless you count "Set-Cookie: " as a fail...]

   When the user agent finishes parsing the Set-Cookie header, the user
   agent *receives a cookie* from the origin server with name cookie-
   name, value cookie-value, and attributes cookie-attribute-list.

5.1.1.  The Max-Age Attribute

   When the user agent receives a cookie attribute with a name string
   that case-insensitively matches the string "Max-Age", the user agent
   MUST process the value string as follows.

   If the first character of the value string is not a DIGIT or a "-"
   character, the user agent MUST ignore the attribute.

   If the remainder of value string contains a non-DIGIT character, the
   user agent MUST ignore the attribute.

   Let delta-seconds be the contents of the value string converted to an
   integer.

   If delta-seconds is less than or equal to 0, then append an attribute
   named Expires (note the name conversion) to the cookie-attribute-list
   with a value equal to the current date and time.

   If delta-seconds is strictly greater than 0, then append an
   attributes named Expires (note the name conversion) to the cookie-
   attribute-list with a value equal to the current date and time plus
   delta-seconds seconds.

5.1.2.  The Expires Attribute

   [TODO: Basically, cookie dates are a mess for historical reasons.]





Barth                   Expires February 22, 2010              [Page 14]


Internet-Draft       HTTP State Management Mechanism         August 2009


      cookie-date       = rfc1123-like-date / mystery-date
      rfc1123-like-date = weekday "," SP rfc1123-like-dmy SP time SP "GMT"
      weekday           = "Monday" / "Mon" / "Tuesday" / "Tue" / ...
      rfc1123-like-dmy  = day dmy-div month dmy-div year
      dmy-div           = SP / "-"
      day               = 2DIGIT / *1SP DIGIT
      month             = "Jan" / "Feb" / ...
      year              = 2DIGIT / 4DIGIT
      time              = 2DIGIT ":" 2DIGIT ":" 2DIGIT

      mystery-date      = *CHAR ; see below


   [TODO: More information about mystery-date.]

5.1.3.  The Domain Attribute

   [TODO]

5.1.4.  The Path Attribute

   The user agent MUST use the following algorithm to compute the
   default-path of a cookie:

   1.  Let uri-path be the path portion of the URI from which the user
       agent received the cookie.  [TODO: Define this more precisely.]

   2.  If the first character of the uri-path is not a "/" character,
       output "/" and skip the remaining steps.

   3.  If the uri-path contains only a single "/" character, output "/"
       and skip the remaining steps.

   4.  Output the characters of the uri-path from the first character up
       to, and but not including, the right-most "/".

   A request-path path-matches a cookie-path if the cookie-path is a
   prefix of the request-path and at least one of the following
   conditions hold:

   o  The last character of the cookie-path is "/".

   o  The first character of the request-path that is not included in
      the cookie-path is a "/" character.

   When the user agent receives a cookie attribute with a name string
   that case-insensitively matches the string "Path", the user agent
   MUST process the value string as follows:



Barth                   Expires February 22, 2010              [Page 15]


Internet-Draft       HTTP State Management Mechanism         August 2009


   o  If the value string is empty, then append an attribute named Path
      to the cookie-attribute-list with a value equal to default-path of
      the cookie.

   o  If the value string is non-empty and the first character is "/",
      then append an attribute named Path to the cookie-attribute-list
      with a value equal to value string.

   o  Otherwise, ignore the attribute.

   [TODO: Test \ ? ; # $ % etc]

5.1.5.  The Secure Attribute

   When the user agent receives a cookie attribute with a name string
   that case-insensitively matches the string "Secure", the user agent
   MUST append an attribute named Secure to the cookie-attribute-list
   with an empty value regardless of the value string.

5.1.6.  The HttpOnly Attribute

   When the user agent receives a cookie attribute with a name string
   that case-insensitively matches the string "HttpOnly", the user agent
   MUST append an attribute named Secure to the cookie-attribute-list
   with an empty value regardless of the value string.

5.2.  Storage Model

   When the user agent receives a cookie, the user agent SHOULD record
   the cookie in its cookie store as follows.

   A user agent MAY ignore received cookies in their entirety if the
   user agent is configured to block receiving cookie for a particular
   response.  For example, the user agent might wish to block receiving
   cookies from "third-party" responses.

   The user agent stores the following fields about each cookie:

   o  name (a sequence of bytes)

   o  value (a sequence of bytes)

   o  expiry (a date)

   o  domain (a cookie-domain)

   o  path (a sequence of bytes)




Barth                   Expires February 22, 2010              [Page 16]


Internet-Draft       HTTP State Management Mechanism         August 2009


   o  creation (a date)

   o  last-access (a date)

   o  persistent (a Boolean)

   o  host-only (a Boolean)

   o  secure-only (a Boolean)

   o  http-only (a Boolean)

   When the user agent receives a cookie, the user agent MUST follow the
   following algorithm:

   1.  Create a new cookie based on the parsed Set-Cookie header:

       1.  Create a new cookie with the following default field values:

           +  name = the cookie-name

           +  value = the cookie-value

           +  expiry = the latest representable date

           +  domain = the request-host

           +  path = the cookie's default-path

           +  last-access = the date and time the cookie was received

           +  last-access = the date and time the cookie was received

           +  persistent = false

           +  host-only = true

           +  secure-only = false

           +  http-only = false

       2.  Update the default field values according to the cookie-
           attributes:

           expiry  If the cookie-attributes contains at least one
              Expires attribute, store the value of the last such
              attribute in the expiry field.  Store the value true in
              the persistent field.  [TODO: Test that this really works



Barth                   Expires February 22, 2010              [Page 17]


Internet-Draft       HTTP State Management Mechanism         August 2009


              when mixing Max-Age and Expires.]

           domain  If the cookie-attributes contains at least one Domain
              attribute, store the value of the last such attribute in
              the domain field.  Store the value false in the host-only
              field.  [TODO: Reject cookies for unrelated domains.]
              [TODO: If the URL's host is an IP address, let Domain to
              be an IP address if it matches the URL's host exactly, but
              set the host-only flag. ]

           path  If the cookie-attributes contains at least one Path
              attribute, store the value of the last such attribute in
              the path field.

           secure-only  If the cookie-attributes contains at least one
              Secure attribute, store the value true in the secure-only
              field.

           http-only  If the cookie-attributes contains at least one
              HttpOnly attribute, store the value true in the http-only
              field.

   2.  Remove from the cookie store all cookies that have the share the
       same name, domain, path, and host-only fields as the newly
       created cookie.  [TODO: Validate this list!]  [TODO: There's some
       funny business around http-only here.]

   3.  Insert the newly created cookie into the cookie store.

   The user agent MUST evict a cookie from the cookie store if A cookie
   exists in the cookie store with an expiry date in the past.

   The user agent MAY evict a cookie from the cookie store if the number
   of cookies sharing a domain field exceeds some predetermined upper
   bound (such as 50 cookies).  [TODO: Explain where 50 comes from.]

   The user agent MAY evict cookies from the cookie store if the cookie
   store exceeds some maximum storage bound (such as 3000 cookies).
   [TODO: Explain where 3000 comes from.]

   When the user agent evicts cookies from the cookie store, the user
   agent MUST evict cookies in the following priority order:

   1.  Cookies with an expiry date in the past.

   2.  Cookies that share a domain field more than a predetermined
       number of other cookies.




Barth                   Expires February 22, 2010              [Page 18]


Internet-Draft       HTTP State Management Mechanism         August 2009


   3.  All other cookies.

   If two cookies have the same removal priority, the user agent MUST
   evict the cookie with the least recent last-access date first.

   When the user agent exits, the user agent MUST remove from the cookie
   store all cookies with the persistent field set to false.

5.3.  The Cookie Header

   When the user agent generates an HTTP request for a particular URI,
   the user agent SHOULD attach exactly one HTTP header named Cookie if
   the cookie-string (defined below) for that URI is non-empty.

   A user agent MAY elide the Cookie header in its entirety if the user
   agent is configured to block sending cookie for a particular request.
   For example, the user agent might wish to block sending cookies
   during "third-party" requests.

   The user agent MUST use the following algorithm to compute the
   cookie-string from a cookie store and from a URI:

   1.  Let cookie-list be the set of cookies from the cookie store that
       meet the following requirements:

       *  The cookie's domain field must domain-match the URI's host.
          [TODO: Spec me]

       *  The cookie's path field must path-match the URI's path.

       *  If the cookie's host-only flag is set, the cookie's domain
          field must denote exactly the same FQDN as the URI's host.
          [TODO: Internet Explorer does not implement this requirement
          but most other major implementations do.]

       *  If the cookie's secure-only field is true, then the URI's
          scheme must denote a "secure" protocol.

             NOTE: The notion of an "secure" protocol is not defined by
             this document.  Typically, user agents consider a protocol
             secure if the protocol makes use of transport-layer
             security, such as TLS.  For example, most user agents
             consider "https" to be a scheme that denotes a secure
             protocol.

       *  If the cookie's http-only field is true, then include the
          cookie only if the user agent is generating the cookie-string
          for use in an HTTP request.



Barth                   Expires February 22, 2010              [Page 19]


Internet-Draft       HTTP State Management Mechanism         August 2009


       NOTE: The Cookie header will not contain any expired cookies
       because cookies past their expiry date are removed from the
       cookie store immediately.

   2.  Sort the cookie-list in the following order:

       *  Cookies with longer path fields are listed before cookies with
          shorter path field.

       *  Among cookies that have equal length path fields, cookies with
          earlier creation dates are listed before cookies with later
          creation dates.

   3.  Update the last-access field of each cookie in the cookie-list to
       the current date.

   4.  Serialize the cookie-list into a cookie-string by processing each
       cookie in the cookie-list in order:

       1.  If the cookie's name field is non-empty, output the cookie's
           name field followed by the character U+3D ("=").

       2.  Output the cookie's value field.

       3.  If there is an unprocessed cookie in the cookie-list, output
           the characters U+3B and U+20 ("; ")

























Barth                   Expires February 22, 2010              [Page 20]


Internet-Draft       HTTP State Management Mechanism         August 2009


6.  Implementation Considerations

6.1.  Set-Cookie Content

   An origin server's content should probably be divided into disjoint
   application areas, some of which require the use of state
   information.  The application areas can be distinguished by their
   request URLs.  The Set-Cookie header can incorporate information
   about the application areas by setting the Path attribute for each
   one.

   The session information can obviously be clear or encoded text that
   describes state.  However, if it grows too large, it can become
   unwieldy.  Therefore, an implementor might choose for the session
   information to be a key to a server-side resource.  [TODO: Describe
   briefly how to generate a decent session key.]

   [TODO: We could recommend that servers encrypt and mac their cookie
   data.]

   [TODO: Mention issues that arise from having multiple concurrent
   sessions.]

6.2.  Implementation Limits

   Practical user agent implementations have limits on the number and
   size of cookies that they can store.  General-use user agents SHOULD
   provide each of the following minimum capabilities:

   o  At least 4096 bytes per cookie (as measured by the size of the
      characters that comprise the cookie non-terminal in the syntax
      description of the Set-Cookie header).  [TODO: Validate]

   o  At least 50 cookies per domain.  [TODO: History lesson]

   o  At least 3000 cookies total.

   The information in a Set-Cookie response header must be retained in
   its entirety.  If for some reason there is inadequate space to store
   the cookie, the cookie must be discarded, not truncated.

   Applications should use as few and as small cookies as possible, and
   they should cope gracefully with the loss of a cookie.  [TODO: Could
   mention latency issues that arise from having tons of cookies.]







Barth                   Expires February 22, 2010              [Page 21]


Internet-Draft       HTTP State Management Mechanism         August 2009


7.  Security Considerations

7.1.  Clear Text

   The information in the Set-Cookie and Cookie headers is transmitted
   in the clear.  Three consequences are:

   1.  Any sensitive information that is conveyed in in the headers is
       exposed to an eavesdropper.

   2.  A malicious intermediary could alter the headers as they travel
       in either direction, with unpredictable results.

   3.  A malicious client could alter the Cookie header before
       transmission, with unpredictable results.

   These facts imply that information of a personal and/or financial
   nature should be sent over a secure channel.  For less sensitive
   information, or when the content of the header is a database key, an
   origin server should be vigilant to prevent a bad Cookie value from
   causing failures.

7.2.  Cookie Spoofing

   [TODO: Mention integrity issue where a sibling domain can inject
   cookies.]

   [TODO: Mention integrity issue where a HTTP can inject cookies into
   HTTPS.]






















Barth                   Expires February 22, 2010              [Page 22]


Internet-Draft       HTTP State Management Mechanism         August 2009


8.  Other, Similar, Proposals

   [TODO: Describe relation to the Netscape Cookie Spec, RFC 2109, RFC
   2629, and cookie-v2.]















































Barth                   Expires February 22, 2010              [Page 23]


Internet-Draft       HTTP State Management Mechanism         August 2009


Appendix A.  Acknowledgements

   This document borrows heavily from RFC 2109.  [TODO: Figure out the
   proper way to credit the authors of RFC 2109.]















































Barth                   Expires February 22, 2010              [Page 24]


Internet-Draft       HTTP State Management Mechanism         August 2009


Appendix B.  Tabled Items

   Tabled items:

   o  Public suffix.














































Barth                   Expires February 22, 2010              [Page 25]


Internet-Draft       HTTP State Management Mechanism         August 2009


Author's Address

   Adam Barth
   University of California, Berkeley

   Email: abarth@eecs.berkeley.edu
   URI:   http://www.adambarth.com/












































Barth                   Expires February 22, 2010              [Page 26]


Html markup produced by rfcmarkup 1.118, available from https://tools.ietf.org/tools/rfcmarkup/