http-state
httpstate                                                       A. Barth
Internet-Draft                                             U.C. Berkeley
Obsoletes: 2109 (if approved)                            January 6, 2010
Intended status: Standards Track
Expires: June 25, July 10, 2010                                 December 22, 2009

                    HTTP State Management Mechanism
                     draft-ietf-httpstate-cookie-00
                     draft-ietf-httpstate-cookie-01

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Abstract

   This document defines the HTTP Cookie and Set-Cookie headers.  These
   headers can be used by HTTP servers to store state on HTTP user
   agents, letting the servers maintain a stateful session over the
   mostly stateless HTTP protocol.  The cookie protocol has many
   historical infelicities and should be avoided for new applications of
   HTTP.

      NOTE: 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  5
     1.1.  Syntax Notation  . . . . . . . . . . . . . . . . . . . . .  4  5
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5  6
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  6  7
     3.1.  Examples . . . . . . . . . . . . . . . . . . . . . . . . .  6  7
   4.  Protocol Description .  A Well-Behaved Profile . . . . . . . . . . . . . . . . . . . .  7  8
     4.1.  Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . .  7  8
       4.1.1.  Syntax . . . . . . . . . . . . . . . . . . . . . . . .  7  8
       4.1.2.  Semantics (Non-Normative)  . . . . . . . . . . . . . . . . . . . . . .  8  9
     4.2.  Cookie . . . . . . . . . . . . . . . . . . . . . . . . . .  9 11
       4.2.1.  Syntax . . . . . . . . . . . . . . . . . . . . . . . .  9 11
       4.2.2.  Semantics  . . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  Controlling Caching 11
   5.  The Cookie Protocol  . . . . . . . . . . . . . . . . . . . 10
   5.  User Agent Conformance . . 12
     5.1.  Algorithms . . . . . . . . . . . . . . . . . . 12
     5.1.  Parsing the Set-Cookie Header . . . . . . 12
       5.1.1.  Dates  . . . . . . . . 12
       5.1.1.  The Max-Age Attribute . . . . . . . . . . . . . . . . 14 12
       5.1.2.  The Expires Attribute  Domains  . . . . . . . . . . . . . . . . . . . . . . . 14
       5.1.3.  The Domain Attribute  Paths  . . . . . . . . . . . . . . . . . 17
       5.1.4.  The Path Attribute . . . . . . . 14
     5.2.  The Set-Cookie Header  . . . . . . . . . . . . 17
       5.1.5.  The Secure Attribute . . . . . . 15
       5.2.1.  The Max-Age Attribute  . . . . . . . . . . . 18
       5.1.6.  The HttpOnly Attribute . . . . . 17
       5.2.2.  The Expires Attribute  . . . . . . . . . . . 18
     5.2.  Storage Model . . . . . 17
       5.2.3.  The Domain Attribute . . . . . . . . . . . . . . . . . 18
     5.3.
       5.2.4.  The Cookie Header Path Attribute . . . . . . . . . . . . . . . . . . 18
       5.2.5.  The Secure Attribute . . 21
   6.  Implementation Considerations . . . . . . . . . . . . . . . 19
       5.2.6.  The HttpOnly Attribute . 23
     6.1.  Set-Cookie Content . . . . . . . . . . . . . . . 19
     5.3.  Storage Model  . . . . . 23
     6.2.  Implementation Limits . . . . . . . . . . . . . . . . . 19
     5.4.  The Cookie Header  . 23
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . 24
     7.1.  Clear Text 21
   6.  Implementation Limits  . . . . . . . . . . . . . . . . . . . . 24
   7.  Security Considerations  . . . . 24
     7.2.  Weak Isolation . . . . . . . . . . . . . . . 25
     7.1.  Clear Text . . . . . . . 24
     7.3.  Cookie Spoofing . . . . . . . . . . . . . . . . . 25
     7.2.  Weak Confidentiality . . . . 24
   8.  Other, Similar, Proposals . . . . . . . . . . . . . . . 25
     7.3.  Weak Integrity . . . . 25
   9.  Normative References . . . . . . . . . . . . . . . . . . 25
   8.  Normative References . . . 26
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . 27
   Appendix B.  Tabled Items  . . A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 28
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 29

1.  Introduction

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

1.1.  Syntax Notation

   This specification uses  Using
   the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234].

   The following core rules are included by reference, as defined in
   [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
   (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
   HEXDIG Set-Cookie header, an HTTP server can store name/value pairs
   (called cookies) at the user agent.  When the user agent makes
   subsequent requests to the server, the user agent will return the
   name/value pairs in the Cookie header.

   Although simple on its surface, the cookie protocol has a number of
   complexities.  For example, the server indicates a scope for each
   cookie when sending them to the user agent.  The scope indicates the
   maximum amount of time the user agent should persist the cookie, to
   which servers the user agent should return the cookie, and for which
   protocols the cookie is applicable.

   For historical reasons, the cookie protocol contains a number of
   security and privacy infelicities.  For example, a server can
   indicate that a given cookie is intended for "secure" connections,
   but the Secure attribute provides only confidentiality (not
   integrity) from active network attackers.  Similarly, cookies for a
   given host are shared across all the ports on that host, even though
   the usual "same-origin policy" used by web browsers isolates content
   retrieved from different ports.

1.1.  Syntax Notation

   This specification uses the Augmented Backus-Naur Form (ABNF)
   notation of [RFC5234].

   The following core rules are included by reference, as defined in
   [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
   (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote),
   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit
   sequence of data), SP (space), HTAB (horizontal tab), VCHAR (any
   visible [USASCII] character), and WSP (whitespace).

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 user
   agent 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

3.  Overview

   We outline here a FQHN.  Hosts names
   can be specified either as way for 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 origin server to the state
   information that passes between an origin server and user agent, and
   that gets stored by the user agent.

3.  Overview

   We outline here a way for an origin server to send 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

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

   Servers may 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 MAY include multiple Set-Cookie headers header fields in a
   single response.  Note that an intervening gateway MUST NOT fold
   multiple Set-Cookie headers header fields into a single header.

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

3.1.  Examples

   [TODO: Put some examples here.

4.  Protocol Description

   The cookie protocol consists of two HTTP headers:  A Well-Behaved Profile

   This section describes the Set-Cookie
   header syntax and semantics of a well-behaved
   profile of the Cookie header.  The server sends protocol.  Servers SHOULD use the Set-Cookie header
   is profile described in
   this section, both to the maximize interoperability with existing user agent in an HTTP response, causing
   agents and because a future version of the user agent to
   modify cookie protocol could
   remove support for some of the Cookie header it returns to most esoteric aspects of the server.

   This section describes protocol.
   User agents, however, MUST implement the syntax and semantics full protocol to ensure
   interoperability with servers making use of the full protocol.
   Detailed conformance requirements for user agents are given in
   Section [TODO].

4.1.  Set-Cookie

   The Set-Cookie header is used to send cookies from the server to the
   user agent.

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.

   [TODO: Consider replacing this grammar with  Servers SHOULD
   NOT send Set-Cookie headers that fail to conform to the one from 2009-11-07-
   Yui-Naruse.txt.] following
   grammar:

   set-cookie-header = "Set-Cookie:" name-value-pairs
     name-value-pairs OWS set-cookie-string OWS
   set-cookie-string = name-value-pair *(";" name-value-pair)
     name-value-pair cookie-pair *( ";" cookie-av)
   cookie-pair       = name ["=" value]        ; optional value
     name cookie-name "=" cookie-value
   cookie-name       = token
     value
   cookie-value      = *CHAR token
   token             = <token, as defined in Section 2.2 of RFC 2616>

   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

   cookie-av         = expires-av / domain-av / path-av /
                       secure-av / httponly-av
   expires-av        = "Expires" "=" cookie-date
   cookie-date       = <rfc1123-date, as optional, some defined in RFC 2616>
   domain-av         = "Domain" "=" domain-value
   domain-value      = token
   path-av           = "Path" "=" path-value
   path-value        = <abs_path, as defined in RFC 2616>
   secure-av         = "Secure"
   httponly-av       = "HttpOnly"

   Servers SHOULD NOT include two attributes require values. with the same name.

   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, is, 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 U+003D ("=") character.  Servers wishing to interoperate with
   some legacy user agents might wish to elide this extra white space to
   maximize compatibility. whitespace.

4.1.2.  Semantics (Non-Normative)

   This section describes a simplified semantics of the Set-Cookie
   header.  These semantics are detailed enough to be useful for
   understanding the most common uses of the cookie protocol.  The full
   semantics are described in Section 5.

   When the user agent receives a Set-Cookie header, the user agent
   stores the cookie in its cookie store.  When the user agent
   subsequently makes
   another an HTTP request to the origin server, request, the user agent returns the consults its
   cookie store and includes the applicable, non-expired cookies in the
   Cookie header.

   The server can override

   If the default handling of cookies by specifying cookie attributes.  User agents ignore unrecognized store already contains a 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 with the maximum
      lifetime of same cookie-
   name, domain-value, and path-value, the cookie, measured in seconds existing cookie is evicted
   from the moment the
      user agent receives the cookie.  If cookie store and replaced with the server does not supply new value.  Notice that
   servers can delete cookies by including an Expires or attribute with a Max-Age attribute,
   value in the lifetime of past.

   Unless the cookie's attributes indicate otherwise, the cookie is
      limited
   returned only to the origin server, and it expires at the end of the
   current session (as defined by the user agent).

4.1.2.2.  Expires

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

   Semantics ignore
   unrecognized cookie attributes.

4.1.2.1.  Expires

   The value of the Expires attribute represents indicates the maximum lifetime of the cookie,
   represented as the point in date and time at which the cookie expires.  If the server does not supply an Expires or a
      Max-Age attribute, the lifetime of the cookie  The
   user agent is limited not required to retain the
      current session (as defined by cookie until the specified
   date has passed.  In fact, user agent).

4.1.2.3.  Domain

   [TODO: Test Domain.]  The agents often evict cookies from the
   cookie store due to memory pressure or privacy concerns.

4.1.2.2.  Domain

   The Domain attribute specifies the domain those hosts for which the cookie is valid.  The will
   be sent.  For example, if the domain attribute contains the value
   ".example.com", the user agent will include the cookie in the Cookie
   header when making HTTP requests to example.com, www.example.com, and
   www.corp.example.com.  (Note that a leading dot isn't required.  If there U+2E ("."), if present,
   is no ignored.)  If the server omits the Domain attribute, the default is to user
   agent will return the cookie only to the origin server.  [TODO: You can only set server
   The user agent will reject cookies (refuse to store them in the
   cookie store) unless the Domain attribute specifies a scope for related
   domains.]

4.1.2.4.  Path

   Syntax  A sequence the
   cookie that would include the origin server.  For example, the user
   agent will accept a Domain attribute of characters beginning with ".example.com" or of
   ".foo.example.com" from foo.example.com, but the user agent will not
   accept a "/" character.

   Semantics Domain attribute of ".bar.example.com" or of
   ".baz.foo.example.com".

   NOTE: For security reasons, some user agents are configured to reject
   Domain attributes that do not correspond to a "registry controlled"
   domain (or a subdomain of a registry controlled domain).  For
   example, some user agents will reject Domain attributes of ".com".

4.1.2.3.  Path

   The Path attribute specifies limits the scope of the cookie
      within to a given FQDN.  The set of paths.
   When a cookie has a Path attribute, the user agent will include a the
   cookie in an HTTP request only if the Request-URI's path matches, or portion of the Request-URI
   matches (or is a subdirectory of, of) the cookie's Path attribute (where attribute, where
   the "/" U+002F ("/") character is interpreted as a directory separator).  The default
      value for separator.
   If the server omits the Path attribute is attribute, the user agent will use the
   directory of the Request-URI
      when Request-URI's path component as the cookie was received.

4.1.2.5.  Secure

   Syntax  Servers MUST NOT include a default value.

   Semantics  The user agent SHOULD protect the confidentiality of

   Although seemingly useful for isolating cookies with between different
   paths within a given domain, the Secure Path attribute by cannot be relied upon
   for security for two reasons: First, user agents do not transmitting Secure
      cookies over an "insecure" channel (where "insecure" is defined by prevent one
   path from overwriting the user agent).

4.1.2.6.  HttpOnly

   Syntax  Servers MUST NOT include cookies for another path.  For example, if
   a value.

   Semantics  The response to a request for /foo/bar.html attempts to set a cookie
   with a Path attribute of "/baz" the user agent SHOULD protect confidentiality of will store that cookie
   in the cookie store.  Second, the "same-origin" policy implemented by
   many user agents does not isolate different paths within an origin.
   For example, /foo/bar.html can read cookies with a Path attribute of
   "/baz" because they are within the HttpOnly "same origin".

4.1.2.4.  Secure

   The Secure attribute limits the scope of the cookie to "secure"
   channels (where "secure" is defined by not revealing their contents the user agent).  When a
   cookie has the Secure attribute, the user agent will include the
   cookie in an HTTP request only if the request is transmitted over a
   secure channel (typically TLS [RFC5234]).

   Although seemingly useful for protecting cookies from active network
   attackers, the Secure attribute protects only the cookie's
   confidentiality.  An active network attacker can overwrite Secure
   cookies from an insecure channel, disrupting the integrity of the
   cookies.

4.1.2.5.  HttpOnly

   The HttpOnly attribute limits the scope of the cookie to HTTP
   requests.  In particular, the attribute instructs the user agent to
   elide the cookie when providing access to its cookie store via
      "non-HTTP" APIs.  (Note that this document does not define which "non-
   HTTP" APIs are "non-HTTP".) (as defined by the user agent).

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 conforms to the grammar requirements in this
   section, the requirements in Section [TODO], the next section will cause the user
   agent might not
   supply to return a Cookie header that conforms to the preceding following
   grammar.

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

   cookie-header = "Cookie:" OWS cookie-string OWS
   cookie-string = cookie-pair *( ";" cookie-pair)
   cookie-pair   = cookie-name "=" cookie-value
   cookie-name   = token
   cookie-value  = token
   token         = <token, as defined in Section 2.2 of RFC 2616>

4.2.2.  Semantics

   Each cookie-pair represents a cookie stored by the value. user agent.  The meaning
   cookie-name and the cookie-value are returned verbatim from the
   corresponding parts of the Set-Cookie header.

   Notice that the cookie attributes are not returned.  In particular,
   the server cannot determine from the Cookie header alone when a
   cookie will expire, for which domains the cookie is valid, for which
   paths the cookie is valid, or whether the cookie was set with the
   Secure or HttpOnly attributes.

   The semantics of individual 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

5.  The Cookie Protocol

   For historical reasons, the effect of possible caching full cookie protocol contains a number of both the returned resource and the Set-Cookie header.  Caching
   "public" documents
   exotic quirks.  This section is desirable.  For example, if intended to specify the origin server
   wants cookie
   protocol in enough detail to use a public document such as enable a "front door" page user agent that implements the
   protocol precisely as a
   sentinel specified to indicate the beginning interoperate with existing
   servers.

   Although some parts of a session for which a Set-
   Cookie response header must be generated, the page should be stored cookie protocol are specified
   algorithmically, user agents are free to implement the cookie
   protocol in caches "pre-expired" so any manner as long as their resultant behavior is "black-
   box" indistinguishable from a user agent that implements the origin server will see further
   requests.  "Private documents", for example those that contain
   information strictly private to protocol
   as described.

5.1.  Algorithms

   This section defines a session, should not be cached in
   shared caches.

   If number of algorithms used by the cookie is intended for
   protocol.

5.1.1.  Dates

   The user agent MUST use by a single user, the Set-Cookie
   header should not be cached.  A Set-Cookie header that is intended following algorithm to
   be shared *parse a cookie-
   date*:

   1.  Using the grammar below, divide the cookie-date into date-tokens.

   cookie-date     = date-token *( 1*delimiter date-token )
   delimiter       = %x09 / %x20 / %x21 / %x22 / %x23 / %x24 /
                     %x25 / %x26 / %x27 / %x28 / %x29 / %x2A /
                     %x2B / %x2C / %x2D / %x2E / %x2F / %x3B /
                     %x3C / %x3D / %x3E / %x3F / %x40 / %x5B /
                     %x5C / %x5D / %x5E / %x5F / %x60 / %x7B /
                     %x7C / %x7D / %x7E
   date-token      = day-of-month / month / year / time / mystery
   day-of-month    = 2DIGIT / DIGIT
   month           = "jan" [ mystery ] / "feb" [ mystery ] /
                     "mar" [ mystery ] / "apr" [ mystery ] /
                     "may" [ mystery ] / "jun" [ mystery ] /
                     "jul" [ mystery ] / "aug" [ mystery ] /
                     "sep" [ mystery ] / "oct" [ mystery ] /
                     "nov" [ mystery ] / "dec" [ mystery ]
   year            = 5DIGIT / 4DIGIT / 3DIGIT / 2DIGIT / DIGIT
   time            = 2DIGIT ":" 2DIGIT ":" 2DIGIT
   mystery         = <anything except a delimiter>
   2.  Process each date-token sequentially in the order the date-tokens
       appear in the cookie-date:

       1.  If the found-day-of-month flag is not set and the date-token
           matches the day-of-month production, set the found-day-of-
           month flag and set the day-of-month-value to the number
           denoted 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 date-token.  Skip the remaining sub-steps and
           continue to the next date-token.

       2.  If the found-month flag is not set and the date-token matches
           the month production, set the found-month flag and set the
           month-value to the month denoted by the date-token.  Skip the
           remaining sub-steps and continue to the Set-Cookie header: Cache-control: no-
      cache="set-cookie". next date-token.

       3.  If the found-year flag is not set 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 date-token matches
           the year production, set the found-year flag and require that it be validated
      before returning it to set 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
           year-value to the
      client: Cache-Control: proxy-revalidate.

   o  To allow caching of a document number denoted by the date-token.  Skip the
           remaining sub-steps and request that it be validated
      before returning it continue to the client (by "pre-expiring" it): Cache-
      Control: max-age=0.  Not all caches will revalidate next date-token.

       4.  If the document
      in every case.

   HTTP/1.1 servers must send Expires: old-date (where old-date found-time flag is a
   date long in not set and 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 token matches the
           time production, set the found-time flag and set the hour-
           value, minute-value, and second-value to the numbers denoted
           by HTTP/1.1
   proxies the digits in addition to the Expires: old-date directive; date-token, respectively.  Skip the Cache-
   Control directive will override
           remaining sub-steps and continue to the Expires: old-date for HTTP/1.1
   proxies.

5.  User Agent Conformance

   Not all origin servers conform next date-token.

   3.  Abort these steps and *fail to parse* if

       *  at least one of the behavior specified in found-day-of-month, found-month, found-
          year, or found-time flags is not set,

       *  the
   previous section.  To ensure interoperability, user agents MUST
   process cookies in a manner that day-of-month-value is "black-box" indistinguishable
   from less than 1 or greater than 31,

       *  the requirements in this section.

5.1.  Parsing year-value is less than 1601 or greater than 30827,

       *  the Set-Cookie Header

   Let an LWS character be either a U+20 (SPACE) hour-value is greater than 23,

       *  the minute-value is greater than 59, or a U+09 (TAB)
   character.

   When a user agent receives an Set-Cookie header in an HTTP response,

       *  the user agent *receives a set-cookie-string* consisting of second-value is greater than 59.

   4.  If the value
   of year-value is greater than 68 and less than 100, increment
       the header.

   A user agent MUST use year-value by 1900.

   5.  If the following algorithm to parse set-cookie-
   strings:

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

   2.  If 0 and less than 69,
       increment the header contains a U+3B (";") character: year-value by 2000.

   6.  Let the name-value-pair string is characters up to, but not
          including, parsed-cookie-date be the first U+3B (";"), date whose day-of-month, month,
       year, hour, minute, and the unparsed-cookie-
          attributes second (in GMT) are the remainder of the header (including day-of-month-
       value, the U+3B
          (";") in question).

       Otherwise: month-value, the name-value-pair string is all year-value, the character contained in hour-value, the header,
       minute-value, and the unparsed-cookie-attributes is the empty
          string.

   3.  If second-value, respectively.

   7.  Return the name-value-pair string contains a U+3D ("=") character: parsed-cookie-date as the (possibly empty) name string result of this algorithm.

5.1.2.  Domains

   A *canonicalized* host-name is the characters up to, but
          not including, host-name converted to lower case.

   A request-host *domain-matches* a cookie-domain if at least one of
   the first U+3D ("=") character, following conditions hold:

   o  The cookie-domain and the
          (possibly empty) value string canonicalized request-host are
      identical.

   o  The cookie-domain is a suffix of the characters after canonicalized request-host,
      the
          first U+3D ("=") character.

       Otherwise: last character of the name string canonicalized request-host that is empty, and not
      included in the value string cookie-domain is the entire
          name-value-pair string.

   4.  Remove any leading or trailing space from the name string a U+002E (".") character, and the
       value string.

   5.  The cookie-name
      request-host is the a host name string, and the cookie-value is (i.e., not an IP address).  [TODO: Is
      this the
       value string. right way to spec this???]

5.1.3.  Paths

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

   1.  If the unparsed-attributes string is empty, skip compute the rest
   *default-path* of
       these steps. a cookie:

   1.  Let uri-path be the path portion of the Request-URI.

   2.  Consume  If the first character of the unparsed-attributes (which
       will be uri-path is not a U+3B (";") character). U+002F ("/")
       character, output U+002F ("/") and skip the remaining steps.

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

          Consume single U+002F ("/") character,
       output U+002F ("/") and skip the remaining steps.

   4.  Output the characters of the unparsed-attributes uri-path from the first character up
       to, but not including, the first U+3B (";") character.

       Otherwise:

          Consume the remainder right-most U+002F ("/").

   A request-path *path-matches* a cookie-path if at least one of the unparsed-attributes.
   following conditions hold: [TODO: This isn't exactly what IE or
   Firefox does.]

   o  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, cookie-path and the
          (possibly empty) value string request-path are identical.

   o  The cookie-path is a prefix of the characters after request-path and the
          first U+3D ("=") last
      character .

       Otherwise: of the name string cookie-path is the entire attribute-value-pair string, and
          the value string U+002F ("/").

   o  The cookie-path 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 a prefix of the name string request-path and the
       value string.

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

          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-string 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. not included in the cookie-
      path is a U+002F ("/") character.

5.2.  The Max-Age Attribute Set-Cookie Header

   When the a user agent receives an Set-Cookie header in an HTTP response,
   the user agent *receives a cookie attribute with a name string
   that case-insensitively matches set-cookie-string* consisting of the string "Max-Age", value
   of the header.

   A user agent MUST process use the value string as follows. following algorithm to parse set-cookie-
   strings:

   1.  If the first character of the value string set-cookie-string is not a DIGIT empty or a "-"
   character, consists entirely of WSP
       characters, the user agent MUST MAY ignore the attribute. set-cookie-string
       entirely.

   2.  If the remainder of value string set-cookie-string contains a non-DIGIT character, U+003B (";") character:

          The name-value-pair string consists of the
   user agent MUST ignore characters up to,
          but not including, the attribute.

   Let delta-seconds be first U+003B (";"), and the contents unparsed-
          attributes consist of the value remainder of the set-cookie-string
          (including the U+003B (";") in question).

       Otherwise:

          The name-value-pair string converted to an
   integer.

   If delta-seconds consists of all the character
          contained in the set-cookie-string, and the unparsed-
          attributes is less than or equal to 0, then append an attribute
   named Expires (note the name conversion) to empty string.

   3.  If the cookie-attribute-list
   with name-value-pair string contains a value equal to U+003D ("=") character:

          The (possibly empty) name string consists of the current date characters up
          to, but not including, the first U+003D ("=") character, and time.

   If delta-seconds is strictly greater than 0, then append an attribute
   named Expires (note
          the (possibly empty) value string consists of the characters
          after the first U+003D ("=") character.

       Otherwise:

          The name conversion) to string is empty, and the cookie-attribute-list
   with a value equal to string consists of the current date and time plus delta-seconds
   seconds.

5.1.2.  The Expires Attribute

   Unfortunately, cookie dates are quite complex for historical reasons.

   When
          entire name-value-pair string.

   4.  Remove any leading or trailing WSP characters from the user agent receives a cookie attribute with a name
       string
   that case-insensitively matches and the string "Expires", value string.

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

   The user agent MUST process use the value string as follows.

   If following algorithm to parse the attribute lacks a value or
   unparsed-attributes:

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

   Using the grammar below, divide

   2.  Consume the value first character of the attribute into date-
   tokens.

         cookie-date     = date-token-list
         date-token-list = date-token [ delimiter date-token-list ]
         delimiter       = %x09 / %x20 / %x21 / %x22 / %x23 / %x24 /
                           %x25 / %x26 / %x27 / %x28 / %x29 / %x2A /
                           %x2B / %x2C / %x2D / %x2E / %x2F / %x3B /
                           %x3C / %x3D / %x3E / %x3F / %x40 / %x5B /
                           %x5C / %x5D / %x5E / %x5F / %x60 / %x7B /
                           %x7C / %x7D / %x7E
         date-token      = day-of-month / month / year / time / mystery
         day-of-month    = 2DIGIT / DIGIT
         month           = "jan" [ mystery ] / "feb" [ mystery ] /
                           "mar" [ mystery ] / "apr" [ mystery ] /
                           "may" [ mystery ] / "jun" [ mystery ] /
                           "jul" [ mystery ] / "aug" [ mystery ] /
                           "sep" [ mystery ] / "oct" [ mystery ] /
                           "nov" [ mystery ] / "dec" [ mystery ]
         year            = 5DIGIT / 4DIGIT / 3DIGIT / 2DIGIT / DIGIT
         time            = 2DIGIT ":" 2DIGIT ":" 2DIGIT
         mystery         = <anything except unparsed-attributes (which
       will be a U+003B (";") character).

   3.  If the remaining unparsed-attributes contains a delimiter>

   Process each data-token sequentially in U+003B (";")
       character:

          Consume the order characters of the date-tokens
   appear in unparsed-attributes up to, but
          not including, the attribute value:

   1. first U+003B (";") character.

       Otherwise:

          Consume the remainder of the unparsed-attributes.

       Let the cookie-av string be the characters consumed in this step.

   4.  If the found-day-of-month flag is cookie-av string contains a U+003D ("=") character:

          The (possibly empty) attribute-name string consists of the
          characters up to, but not set including, the first U+003D ("=")
          character, and the token matches (possibly empty) attribute-value string
          consists of the day-of-month production, set characters after the found-day-of-month flag first U+003D ("=")
          character.

       Otherwise:

          The attribute-name string consists of the entire cookie-av
          string, and
       set the day-of-month-value to attribute-value string is empty.  (Note that
          this step differs from the number denoted by analogous step when parsing the token.
       Skip
          name-value-pair string.)

   5.  Remove any leading or trailing WSP characters from the remaining sub-steps attribute-
       name string and continue to the next token.

   2.  If attribute-value string.

   6.  Process the found-month flag is not set attribute-name and attribute-value according to the token matches
       requirements in the
       month production, set following subsections.

   7.  Return to Step 1.

   When the found-month flag and set user agent finishes parsing the set-cookie-string, the user
   agent *receives a cookie* from the month- Request-URI with name cookie-name,
   value to cookie-value, and attributes cookie-attribute-list.

5.2.1.  The Max-Age Attribute

   If the month denoted by attribute-name case-insensitively matches the token.  Skip string "Max-
   Age", the remaining sub-
       steps and continue to user agent MUST process the next token.

   3. cookie-av as follows.

   If the found-year flag first character of the attribute-value is not set and the token matches the year
       production, set the found-year flag and set a DIGIT or a "-"
   character, ignore the year-value to cookie-av.

   If the
       number denoted by remainder of attribute-value contains a non-DIGIT character,
   ignore the token.  Skip cookie-av.

   Let delta-seconds be the remaining sub-steps and
       continue attribute-value converted to the next token.

   4. an integer.

   If the found-time flag delta-seconds is not set and the token matches the time
       production, set less than or equal to zero (0), let expiry-time
   be the found-time flag current date and set time.  Otherwise, let the hour-value,
       minute-value, expiry-time be the
   current date and second-value time plus delta-seconds seconds.

   Append an attribute to the numbers denoted by the
       digits in the token, respectively.  Skip cookie-attribute-list with an attribute-
   name of Expires (note the remaining sub-steps name conversion) and continue to the next token.

   Abort these steps if

   o  at least one an attribute-value of
   expiry-time.

5.2.2.  The Expires Attribute

   If the found-day-of-month, found-month, found-year,
      or found-time flags is not set,

   o attribute-name case-insensitively matches the day-of-month-value is less than 1 or greater than 31,

   o string
   "Expires", the year-value is less than 1601 or greater than 30827,

   o user agent MUST process the hour-value is greater than 23,

   o cookie-av as follows.

   Let the minute-value is greater than 59, or

   o parsed-cookie-date be the second-value is greater than 59. result of parsing the attribute-
   value as cookie-date.

   If the year-value is greater than 68 and less than 100, increment attribute-value failed to parse as a cookie date, ignore the
   year-value by 1900.
   cookie-av.

   If the year-value is greater than or equal to 0 user agent received the set-cookie-string from an HTTP
   response that contains a Date header field and less than 69,
   increment the year-value by 2000.

   Let contents of the expiry-time
   last Date header field successfully parse as a cookie-date:

      Let server-date be the date whose day-of-month, month, year,
   hour, minute, and second (in GMT) are obtained by parsing the day-of-month-value, contents of
      the
   month-value, last Date header field as a cookie-date.

      Let delta-seconds be the year-value, number of seconds between the server-date
      and the parsed-cookie-date (i.e., parsed-cookie-date - server-
      date).

      Let the hour-value, expiry-time be the minute-value, current date and time plus delta-
      seconds seconds.

   Otherwise:

      Let the second-value, respectively. expiry-time be the parsed-cookie-date.

   If the expiry-time is later than the last date the user agent can
   represent, the user agent MAY replace the expiry-time with the last
   representable date.

   If the expiry-time is earlier than the first date the user agent can
   represent, the user agent MAY replace the expiry-time with the first
   representable date.

   Append an attribute named Expires to the cookie-attribute-list with a
   value equal to an attribute-
   name of Expires and an attribute-value of expiry-time.

5.1.3.

5.2.3.  The Domain Attribute

   When

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

   o follows.

   If the value string attribute-value is empty, then ignore the attribute.  [TODO:
      Add a test for this with multiple Domain attributes.]

   o  If the first character of the value string is ".", then append an
      attribute named Domain to the cookie-attribute-list with a value
      equal to value string excluding the leading "." character.

   o  If the first character of the value string behavior is not ".", then append
      an attribute named Domain to the cookie-attribute-list with a
      value equal to value string and mark the attribute as host-only.

   o  [TODO: Deal with domains that have an insufficient number of
      fields.]

   o  Otherwise, ignore the attribute.

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 undefined.  However,
   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 SHOULD ignore the remaining steps.

   3. cookie-av entirely.

   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 attribute-value string is not included in U+002E ("."):

      Let cookie-domain be the cookie-path is a "/" attribute-value without the leading
      U+002E (".") character.

   When

   Otherwise:

      Let cookie-domain be the user agent receives a cookie entire attribute-value.

   Convert the cookie-domain to lower case.

   [TODO: Test ".127.0.0.1" and "127.0.0.1"]

   Append an attribute to the cookie-attribute-list with a an attribute-
   name string
   that of Domain and an attribute-value of cookie-domain.

5.2.4.  The Path Attribute

   If the attribute-name case-insensitively matches the string "Path",
   the user agent MUST process the value string cookie-av as follows:

   o follows.

   If the value string attribute-value is empty, then append an attribute named Path
      to empty or if the cookie-attribute-list with a value equal to default-path first character of the cookie.
   attribute-value is not U+002F ("/"):

      Let cookie-path be the default-path.  [TODO: Is this right if there are We need more than one path
      attribute?]

   o  If the value string is non-empty tests
      for this, including with " characters and with multiple Path
      attributes.]

   Otherwise:

      Let cookie-path be the first character is "/",
      then append attribute-value.

   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. an attribute-
   name of Path and an attribute-value of cookie-path.

5.2.5.  The Secure Attribute

   When

   If the user agent receives a cookie attribute with a name string
   that attribute-name 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 attribute-name of the value string.

5.1.6. Secure and an empty attribute-value.

5.2.6.  The HttpOnly Attribute

   When

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

5.2. Secure and an empty
   attribute-value.

5.3.  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 a received cookies cookie in their its entirety if the user
   agent is configured to block receiving cookie for a particular
   response. cookies.  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)

   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) name,
   value, expiry-time, domain, path, creation-time, last-access-time,
   persistent-flag, host-only-flag, secure-only-flag, and http-only-
   flag.

   When the user agent receives a cookie, cookie from a Request-URI with name
   cookie-name, value cookie-value, and attributes cookie-attribute-
   list, the user agent MUST follow process the
   following algorithm:

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

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

           + name = the cookie-name

           + cookie-name, value = the cookie-value

           +  expiry = cookie-value.
        Set the latest representable date

           +  domain = the request-host

           +  path = creation-time and the cookie's default-path

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

           +  persistent = false

           +  host-only = true

           +  secure-only = false

           +  http-only = false time.

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

           expiry   If the cookie-attributes cookie-attribute-list contains at least one valid
              Expires attribute, store an attribute with an
        attribute-name of "Expires":

           Set the expiry-value cookie's persistent-flag to true.

           Set the cookie's expiry-time to attribute-value of the last such
           attribute in the expiry field.  Store the value true in
              the persistent field. cookie-attribute-list with an attribute-name
           of "Expires".  [TODO: Test that this really works when mixing
           Max-Age and Expires.]

           domain

        Otherwise:

           Set the cookie's persistent-flag to false.

           Set the cookie's expiry-time to the latest representable
           date.

   3.   If the cookie-attributes cookie-attribute-list contains at least one Domain
              attribute, store an attribute with an
        attribute-name of "Domain":

           Let the value domain-attribute be the attribute-value of the last such
           attribute in the cookie-attribute-list with an attribute-name
           of "Domain".

           If the Request-URI's host does not domain-match the domain-
           attribute, ignore the cookie entirely and abort these steps.

           Set the cookie's host-only-flag to false.

           Set the cookie's domain field.  Store to the value false in domain-attribute.

        Otherwise:

           Set the host-only
              field.  [TODO: Reject cookies for unrelated domains.]
              [TODO: If cookie's host-only-flag to true.

           Set the URL's host is an IP address, let Domain cookie's domain to
              be an IP address if it matches the URL's host exactly, but
              set of the host-only flag. ]

           path Request-URI.

   4.   If the cookie-attributes cookie-attribute-list contains at least one Path
              attribute, store an attribute with an
        attribute-name of "Path", set the cookie's path to attribute-
        value of the last such attribute in the cookie-attribute-list with an
        attribute-name of "Path".  Otherwise, set cookie's path field.

           secure-only to the
        default-path of the Request-URI.

   5.   If the cookie-attributes cookie-attribute-list contains at least one
              Secure attribute, store the value true in an attribute with an
        attribute-name of "Secure", set the secure-only
              field.

           http-only cookie's secure-only-flag to
        true.  Otherwise, set cookie's secure-only-flag to false.

   6.   If the cookie-attributes cookie-attribute-list contains at least one
              HttpOnly attribute, store the value true in an attribute with an
        attribute-name of "HttpOnly", set the http-only
              field.

   2. cookie's http-only-flag to
        true.  Otherwise, set cookie's http-only-flag to false.

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

   3.

   8.   If the cookie's name and value are both empty, abort these
        steps.

   9.   If the cookie's expiry-time is not in the future, abort these
        steps.

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

   The user agent MUST evict a cookie from the cookie store if A if, at any
   time, 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 a cookie from the cookie store if the cookie
   store exceeds some maximum storage predetermined upper bound (such as 3000 cookies).
   [TODO: Explain where 3000 comes from.]

   When the user agent evicts cookies a cookie 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 with more than a predetermined
       number of other cookies.

   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 current session is over", over" (as defined by the user agent),
   the user agent MUST remove from the cookie store all cookies with the persistent field
   persistent-flag set to false.

      NOTE: This document does not define when "the current session is
      over."  Many user agents remove non-persistent cookies when they
      exit.  However, other user agent expire non-persistent cookies
      using other heuristics.

5.3.

5.4.  The Cookie Header

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

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

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

       *  Either:

             The cookie's path field must path-match host-only-flag is true and the URI's path.

       *  If canonicalized
             request-host is identical to the cookie's host-only flag domain.

          Or:

             The cookie's host-only-flag is set, false and the request-host
             domain-matches 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.] domain.

       *  The Request-URI's path patch-matches cookie's path.

       *  If the cookie's secure-only field is true, then the Request-
          URI's scheme must denote a "secure" protocol. protocol (as defined by
          the user agent).

             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 unless the cookie-string is begin generated for a "non-
          HTTP" API.  (Note that this document does not define which
          APIs are "non-HTTP".)

       NOTE: The Cookie header will not contain any expired cookies
       because cookies past their expiry date are removed from to be a scheme that denotes a secure
             protocol.

       *  If the cookie's http-only field is true, then exclude the
          cookie store immediately. unless the cookie-string is begin generated for a
          "HTTP" API (as defined by the user agent).

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

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

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

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

   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 and value fields are both empty, skip
           the remaining steps for this cookie and continue to the next
           cookie, if any.

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

       3. U+003D ("=") character.

       2.  Output the cookie's value field.

       4. value.

       3.  If there is an unprocessed cookie in the cookie-list, output
           the characters U+3B U+003B and U+20 U+0020 ("; ") ").

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 Limits

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

   o  At least 4096 bytes per cookie (as measured by their
   request URLs.  The Set-Cookie the sum of the
      length of the cookie's name, value, and attributes).

   o  At least 50 cookies per domain.

   o  At least 3000 cookies total.

   Servers SHOULD use as few and as small cookies as possible to avoid
   reaching these implementation limits and to avoid network latency due
   to the Cookie header can incorporate information
   about being included in every request.

   Servers should gracefully degrade if the application areas by setting user agent fails to return
   one or more cookies in the Path attribute for each
   one. Cookie header because the user agent might
   evict any cookie at any time on orders from the user.

7.  Security Considerations

7.1.  Clear Text

   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 in the session Set-Cookie and Cookie headers is transmitted
   in the clear.

   1.  All sensitive information conveyed in these headers is exposed to be a key to a server-side resource.  [TODO: Describe
   briefly how to generate a decent session key.]

   [TODO: We
       an eavesdropper.

   2.  A malicious intermediary could recommend that servers 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.

   Servers SHOULD encrypt and mac sign their cookies.  However, encrypting
   and signing cookies does not prevent an attacker from transplanting a
   cookie
   data.]

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

6.2.  Implementation Limits

   Practical one user agent implementations have limits on the number to another.

   In addition to encrypting and
   size signing the the contents of cookies every
   cookie, servers that they can store.  General-use user agents SHOULD
   provide each require a higher level of security SHOULD use
   the following minimum capabilities:

   o  At least 4096 bytes per cookie (as measured protocol only over a secure channel.

7.2.  Weak Confidentiality

   Cookies do provide isolation by port.  If a cookie is readable by a
   service running on one port, the size cookie is also readable by a service
   running on another port of the
      characters that comprise same server.  If a cookie is writable
   by a service on one port, the cookie non-terminal in is also writable by a service
   running on another port of the syntax
      description same server.  For this reason, servers
   SHOULD NOT both run mutually distrusting services on different ports
   of the Set-Cookie header).  [TODO: Validate]

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

   o  At least 3000 same machine and use 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 security-sensitive
   information.

   Cookies do not provide isolation by scheme.  Although most commonly
   used with the cookie, http and https schemes, the cookie must be discarded, not truncated.

   Applications should use cookies for a given host
   are also available to other schemes, such as few ftp and gopher.  This
   lack of isolation is most easily seen when a user agent retrieves a
   URI with a gopher scheme via HTTP, but the lack of isolation by
   scheme is also apparent via non-HTTP APIs that permit access to
   cookies, such as small cookies as possible, HTML's document.cookie API.

7.3.  Weak Integrity

   Cookies do not integrity guarantees for sibling domains (and their
   subdomains).  For example, consider foo.example.com and
   they should cope gracefully
   bar.example.com.  The foo.example.com server can set a cookie with the loss of a cookie.  [TODO: Could
   mention latency issues that arise from having tons
   Domain attribute of cookies.]

7.  Security Considerations

7.1.  Clear Text

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

   1.  Any sensitive information user agent will include
   that is conveyed in cookie in HTTP requests to bar.example.com.  In the headers is
       exposed worst case,
   bar.example.com will be unable to distinguish this cookie from a
   cookie it set itself.  The foo.example.com server might be able to
   leverage this ability to mount 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 attack against bar.example.com.

   Similarly, an active network attacker can inject cookies into the
   Cookie header before
       transmission, with unpredictable results.

   These facts imply that information of a personal and/or financial
   nature should be sent over to https://example.com/ by impersonating a secure channel.  For less sensitive
   information, or when the content of the header is
   response from http://example.com/ and injecting a database key, an
   origin Set-Cookie header.
   The HTTPS server should at example.com will be vigilant unable to prevent a bad Cookie value distinguish these
   cookies from
   causing failures.

7.2.  Weak Isolation

   [TODO: Weak isolation by port.]

   [TODO: Weak isolation cookies that it set itself in an HTTPS response.  An
   active network attacker might be able to leverage this ability to
   mount an attack against example.com even if example.com uses HTTPS
   exclusively.

   Servers can partially mitigate these attacks by scheme (e.g., ftp, gopher, etc).]

7.3.  Cookie Spoofing

   [TODO: Mention integrity encrypting and
   signing their cookies.  However, using cryptography does not fully
   ameliorate the issue where a sibling domain because an attacker can inject
   cookies.]

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

8.  Other, Similar, Proposals

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

9. authentic example.com server in the user's
   session, with unpredictable results.

8.  Normative References

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

Appendix A.  Acknowledgements

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

Appendix B.  Tabled Items

   Tabled items:

   o  Public suffix.

Author's Address

   Adam Barth
   University of California, Berkeley

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