draft-ietf-httpstate-cookie-07.txt   draft-ietf-httpstate-cookie-08.txt 
httpstate A. Barth httpstate A. Barth
Internet-Draft U.C. Berkeley Internet-Draft U.C. Berkeley
Obsoletes: 2109 (if approved) April 18, 2010 Obsoletes: 2109 (if approved) April 23, 2010
Intended status: Standards Track Intended status: Standards Track
Expires: October 20, 2010 Expires: October 25, 2010
HTTP State Management Mechanism HTTP State Management Mechanism
draft-ietf-httpstate-cookie-07 draft-ietf-httpstate-cookie-08
Abstract Abstract
This document defines the HTTP Cookie and Set-Cookie headers. These This document defines the HTTP Cookie and Set-Cookie headers. These
headers can be used by HTTP servers to store state (called cookies) headers can be used by HTTP servers to store state (called cookies)
at HTTP user agents, letting the servers maintain a stateful session at HTTP user agents, letting the servers maintain a stateful session
over the mostly stateless HTTP protocol. Although cookies have many over the mostly stateless HTTP protocol. Although cookies have many
historical infelicities that degrade their security and privacy, the historical infelicities that degrade their security and privacy, the
Cookie and Set-Cookie headers are widely used on the Internet. Cookie and Set-Cookie headers are widely used on the Internet.
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 20, 2010. This Internet-Draft will expire on October 25, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. General Nonsense . . . . . . . . . . . . . . . . . . . . . . . 6 2. General Nonsense . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Conformance Criteria . . . . . . . . . . . . . . . . . . . 6 2.1. Conformance Criteria . . . . . . . . . . . . . . . . . . . 6
2.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6 2.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Server Requirements . . . . . . . . . . . . . . . . . . . . . 10 4. Server Requirements . . . . . . . . . . . . . . . . . . . . . 10
4.1. Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Set-Cookie . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.2. Semantics (Non-Normative) . . . . . . . . . . . . . . 11 4.1.2. Semantics (Non-Normative) . . . . . . . . . . . . . . 11
4.2. Cookie . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2. Cookie . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.2. Semantics . . . . . . . . . . . . . . . . . . . . . . 14 4.2.2. Semantics . . . . . . . . . . . . . . . . . . . . . . 14
5. User Agent Requirements . . . . . . . . . . . . . . . . . . . 15 5. User Agent Requirements . . . . . . . . . . . . . . . . . . . 15
5.1. Algorithms . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1. Algorithms . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. Dates . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1.1. Dates . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1.2. Domains . . . . . . . . . . . . . . . . . . . . . . . 17 5.1.2. Domains . . . . . . . . . . . . . . . . . . . . . . . 17
5.1.3. Paths . . . . . . . . . . . . . . . . . . . . . . . . 17 5.1.3. Paths . . . . . . . . . . . . . . . . . . . . . . . . 17
5.2. The Set-Cookie Header . . . . . . . . . . . . . . . . . . 18 5.2. The Set-Cookie Header . . . . . . . . . . . . . . . . . . 18
5.2.1. The Expires Attribute . . . . . . . . . . . . . . . . 20 5.2.1. The Expires Attribute . . . . . . . . . . . . . . . . 20
5.2.2. The Max-Age Attribute . . . . . . . . . . . . . . . . 20 5.2.2. The Max-Age Attribute . . . . . . . . . . . . . . . . 20
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This document defines the HTTP Cookie and Set-Cookie headers. Using This document defines the HTTP Cookie and Set-Cookie headers. Using
the Set-Cookie header, an HTTP server can store name/value pairs and the Set-Cookie header, an HTTP server can store name/value pairs and
associated metadata (called cookies) at the user agent. When the associated metadata (called cookies) at the user agent. When the
user agent makes subsequent requests to the server, the user agent user agent makes subsequent requests to the server, the user agent
uses the metadata to determine whether to return the name/value pairs uses the metadata to determine whether to return the name/value pairs
in the Cookie header. in the Cookie header.
Although simple on its surface, cookies have a number of Although simple on its surface, cookies have a number of
complexities. For example, the server indicates a scope for each complexities. For example, the server indicates a scope for each
cookie when sending them to the user agent. The scope indicates the cookie when sending them to the user agent. The scope indicates the
maximum amount of time the user agent should retain the cookie, to maximum amount of time the user agent should return the cookie, the
which servers the user agent should return the cookie, and for which servers to which the user agent should return the cookie, and the
protocols the cookie is applicable. protocols for which the cookie is applicable.
For historical reasons, cookies contain a number of security and For historical reasons, cookies contain a number of security and
privacy infelicities. For example, a server can indicate that a privacy infelicities. For example, a server can indicate that a
given cookie is intended for "secure" connections, but the Secure given cookie is intended for "secure" connections, but the Secure
attribute provides only confidentiality (not integrity) from active attribute provides only confidentiality (not integrity) from active
network attackers. Similarly, cookies for a given host are shared network attackers. Similarly, cookies for a given host are shared
across all the ports on that host, even though the usual "same-origin across all the ports on that host, even though the usual "same-origin
policy" used by web browsers isolates content retrieved from policy" used by web browsers isolates content retrieved from
different ports. different ports.
Prior to this document, there were at least three descriptions of
cookies: the so-called "Netscape cookie specification," RFC 2109
[RFC2109], and RFC 2965 [RFC2965]. However, none of these documents
describe how the Cookie and Set-Cookie headers are actually used on
the Internet. By contrast, this document attempts to specify the
syntax and semantics of these headers as they are actually used on
the Internet.
2. General Nonsense 2. General Nonsense
2.1. Conformance Criteria 2.1. Conformance Criteria
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in document are to be "RECOMMENDED", "MAY", and "OPTIONAL" in document are to be
interpreted as described in [RFC2119]. interpreted as described in [RFC2119].
Requirements phrased in the imperative as part of algorithms (such as Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and abort these "strip any leading space characters" or "return false and abort these
steps") are to be interpreted with the meaning of the key word steps") are to be interpreted with the meaning of the key word
("MUST", "SHOULD", "MAY", etc) used in introducing the algorithm. ("MUST", "SHOULD", "MAY", etc) used in introducing the algorithm.
Conformance requirements phrased as algorithms or specific steps can
be implemented in any manner, so long as the end result is
equivalent. In particular, the algorithms defined in this
specification are intended to be easy to understand and are not
intended to be performant.
2.2. Syntax Notation 2.2. Syntax Notation
This specification uses the Augmented Backus-Naur Form (ABNF) This specification uses the Augmented Backus-Naur Form (ABNF)
notation of [RFC5234]. notation of [RFC5234].
The following core rules are included by reference, as defined in The following core rules are included by reference, as defined in
[RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF [RFC5234], Appendix B.1: ALPHA (letters), CR (carriage return), CRLF
(CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), (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 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 sequence of data), SP (space), HTAB (horizontal tab), CHAR (any US-
visible [USASCII] character), and WSP (whitespace). ASCII character), VCHAR (any visible US-ASCII character), and WSP
(whitespace).
The OWS (optional whitespace) rule is used where zero or more linear The OWS (optional whitespace) rule is used where zero or more linear
whitespace characters may appear. OWS SHOULD either not be produced whitespace characters MAY appear:
or be produced as a single SP character. Multiple OWS characters
that occur within field-content SHOULD be replaced with a single SP OWS = *( [ obs-fold ] WSP )
before interpreting the field value or forwarding the message ; "optional" whitespace
downstream. obs-fold = CRLF
OWS SHOULD either not be produced or be produced as a single SP
character. Multiple OWS characters that occur within field-content
SHOULD be replaced with a single SP before interpreting the field
value or forwarding the message downstream.
2.3. Terminology 2.3. Terminology
The terms user agent, client, server, proxy, and origin server have The terms user agent, client, server, proxy, and origin server have
the same meaning as in the HTTP/1.1 specification ([RFC2616]). the same meaning as in the HTTP/1.1 specification ([RFC2616]).
The terms request-host and request-URI refer to the values the user The terms request-host and request-uri refer to the values the user
agent would send to the server as, respectively, the host (but not 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 port) and the absoluteURI (http_URL) of the HTTP Request-Line.
Request-Line.
3. Overview 3. Overview
We outline here a way for an origin server to send state information We outline here a way for an origin server to send state information
to a user agent and for the user agent to return the state to a user agent and for the user agent to return the state
information to the origin server. information to the origin server.
To store state, the origin server includes a Set-Cookie header in an To store state, the origin server includes a Set-Cookie header in an
HTTP response. In subsequent requests, the user agent returns a HTTP response. In subsequent requests, the user agent returns a
Cookie request header to the origin server. The Cookie header Cookie request header to the origin server. The Cookie header
contains a number of cookies the user agent received in previous Set- contains a number of cookies the user agent received in previous Set-
Cookie headers. The origin server is free to ignore the Cookie Cookie headers. The origin server is free to ignore the Cookie
header or use its contents for an application-defined purpose. The header or use its contents for an application-defined purpose. The
origin server MAY send the user agent a Set-Cookie response header origin server MAY send the user agent a Set-Cookie response header
with the same or different information, or it MAY send no Set-Cookie with the same or different information, or it MAY send no Set-Cookie
header at all. header at all.
Servers MAY return a Set-Cookie response header with any response. Servers MAY return a Set-Cookie response header with any response.
User agents SHOULD send a Cookie request header, subject to other
rules detailed below, with every request.
An origin server MAY include multiple Set-Cookie header fields in a An origin server MAY include multiple Set-Cookie header fields in a
single response. Note that an intervening gateway MUST NOT fold single response. Gateways that wish to be transparent to cookies
multiple Set-Cookie header fields into a single header field. MUST NOT fold multiple Set-Cookie header fields into a single header
field.
If a server sends multiple responses containing Set-Cookie headers
concurrently to the user agent (e.g., when communicating with the
user agent over multiple sockets), these responses create a "race
condition" that can lead to unpredictable behavior.
3.1. Examples 3.1. Examples
Using the Set-Cookie header, a server can send the user agent a short Using the Set-Cookie header, a server can send the user agent a short
string in an HTTP response that the user agent will return in future string in an HTTP response that the user agent will return in future
HTTP requests. For example, the server can send the user agent a HTTP requests. For example, the server can send the user agent a
"session identifier" named SID with the value 31d4d96e407aad42. The "session identifier" named SID with the value 31d4d96e407aad42. The
user agent then returns the session identifier in subsequent user agent then returns the session identifier in subsequent
requests. requests.
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== User Agent -> Server == == User Agent -> Server ==
Cookie: SID=31d4d96e407aad42 Cookie: SID=31d4d96e407aad42
The server can alter the default scope of the cookie using the Path The server can alter the default scope of the cookie using the Path
and Domain attributes. For example, the server can instruct the user and Domain attributes. For example, the server can instruct the user
agent to return the cookie to every path and every subdomain of agent to return the cookie to every path and every subdomain of
example.com. example.com.
== Server -> User Agent == == Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42; Path=/; Domain=.example.com Set-Cookie: SID=31d4d96e407aad42; Path=/; Domain=example.com
== User Agent -> Server == == User Agent -> Server ==
Cookie: SID=31d4d96e407aad42 Cookie: SID=31d4d96e407aad42
The server can store multiple cookies at the user agent. For The server can store multiple cookies at the user agent. For
example, the server can store a session identifier as well as the example, the server can store a session identifier as well as the
user's preferred language by returning two Set-Cookie header fields. user's preferred language by returning two Set-Cookie header fields.
Notice that the server uses the Secure and HttpOnly attributes to Notice that the server uses the Secure and HttpOnly attributes to
provide additional security protections for the more-sensitive provide additional security protections for the more-sensitive
session identifier. session identifier.
== Server -> User Agent == == Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42; Path=/; Secure; HttpOnly Set-Cookie: SID=31d4d96e407aad42; Path=/; Secure; HttpOnly
Set-Cookie: lang=en-US; Path=/; Domain=.example.com Set-Cookie: lang=en-US; Path=/; Domain=example.com
== User Agent -> Server == == User Agent -> Server ==
Cookie: SID=31d4d96e407aad42; lang=en-US Cookie: SID=31d4d96e407aad42; lang=en-US
If the server wishes the user agent to persist the cookie over If the server wishes the user agent to persist the cookie over
multiple sessions, the server can specify a expiration date in the multiple sessions, the server can specify a expiration date in the
Expires attribute. Note that the user agent might delete the cookie Expires attribute. Note that the user agent might delete the cookie
before the expiration date if the user agent's cookie store exceeds before the expiration date if the user agent's cookie store exceeds
its quota or if the user manually deletes the server's cookie. its quota or if the user manually deletes the server's cookie.
== Server -> User Agent == == Server -> User Agent ==
Set-Cookie: lang=en-US; Expires=Wed, 09 Jun 2021 10:18:14 GMT Set-Cookie: lang=en-US; Expires=Wed, 09 Jun 2021 10:18:14 GMT
== User Agent -> Server == == User Agent -> Server ==
Cookie: lang=en-US Cookie: SID=31d4d96e407aad42; lang=en-US
Finally, to remove a cookie, the server returns a Set-Cookie header Finally, to remove a cookie, the server returns a Set-Cookie header
with an expiration date in the past. The server will be successful with an expiration date in the past. The server will be successful
in removing the cookie only if the Path and the Domain attribute in in removing the cookie only if the Path and the Domain attribute in
the Set-Cookie header match the values used when the cookie was the Set-Cookie header match the values used when the cookie was
created. created.
== Server -> User Agent == == Server -> User Agent ==
Set-Cookie: lang=; Expires=Sun, 06 Nov 1994 08:49:37 GMT Set-Cookie: lang=; Expires=Sun, 06 Nov 1994 08:49:37 GMT
== User Agent -> Server == == User Agent -> Server ==
(No Cookie header) Cookie: SID=31d4d96e407aad42
4. Server Requirements 4. Server Requirements
This section describes the syntax and semantics of a well-behaved This section describes the syntax and semantics of a well-behaved
profile of the Cookie and Set-Cookie headers. Servers SHOULD use the profile of the Cookie and Set-Cookie headers. Servers SHOULD use the
profile described in this section, both to maximize interoperability profile described in this section, both to maximize interoperability
with existing user agents and because a future version of the Cookie with existing user agents and because a future version of the Cookie
or Set-Cookie headers could remove support for some of the most or Set-Cookie headers could remove support for some of the most
esoteric semantics. User agents, however, MUST implement the full esoteric semantics. User agents, however, MUST implement the full
semantics to ensure interoperability with servers making use of the semantics to ensure interoperability with servers making use of the
full semantics. full semantics.
4.1. Set-Cookie 4.1. Set-Cookie
The Set-Cookie header is used to send cookies from the server to the The Set-Cookie header is used to send cookies from the server to the
user agent. user agent.
4.1.1. Syntax 4.1.1. Syntax
Informally, the Set-Cookie response header comprises the token Set- Informally, the Set-Cookie response header contains the header name
Cookie:, followed by a cookie. Each cookie begins with a name-value- "Set-Cookie" followed by a ":" and a cookie. Each cookie begins with
pair, followed by zero or more attribute-value pairs. Servers SHOULD a name-value pair, followed by zero or more attribute-value pairs.
NOT send Set-Cookie headers that fail to conform to the following Servers SHOULD NOT send Set-Cookie headers that fail to conform to
grammar: the following grammar:
set-cookie-header = "Set-Cookie:" OWS set-cookie-string OWS set-cookie-header = "Set-Cookie:" SP set-cookie-string
set-cookie-string = cookie-pair *( ";" cookie-av ) set-cookie-string = cookie-pair *( ";" SP cookie-av )
cookie-pair = cookie-name "=" cookie-value cookie-pair = cookie-name "=" cookie-value
cookie-name = token cookie-name = token
cookie-value = token cookie-value = token
token = <token, as defined in RFC 2616> token = <token, as defined in RFC 2616>
cookie-av = expires-av / max-age-av / domain-av / cookie-av = expires-av / max-age-av / domain-av /
path-av / secure-av / httponly-av path-av / secure-av / httponly-av /
expires-av = "Expires" "=" sane-cookie-date extension-av
expires-av = "Expires=" sane-cookie-date
sane-cookie-date = <rfc1123-date, as defined in RFC 2616> sane-cookie-date = <rfc1123-date, as defined in RFC 2616>
max-age-av = "Max-Age" "=" 1*DIGIT max-age-av = "Max-Age=" 1*DIGIT
domain-av = "Domain" "=" domain-value domain-av = "Domain=" domain-value
domain-value = token domain-value = <subdomain, as defined in RFC 1034>
path-av = "Path" "=" path-value path-av = "Path=" path-value
path-value = <abs_path, as defined in RFC 2616> path-value = <abs_path, except those containing ";">
secure-av = "Secure" secure-av = "Secure"
httponly-av = "HttpOnly" httponly-av = "HttpOnly"
extension-av = <any CHAR except CTLs or ";">
Servers SHOULD NOT include two attributes with the same name. Servers SHOULD NOT include two attributes with the same name.
Servers SHOULD NOT include two Set-Cookie header fields in the same Servers SHOULD NOT include two Set-Cookie header fields in the same
response with the same cookie-name. response with the same cookie-name.
The cookie-value is opaque to the user agent and MAY be anything the The cookie-value is opaque to the user agent and MAY be anything the
origin server chooses to send. "Opaque" implies that the content is origin server chooses to send. "Opaque" implies that the content is
of interest and relevance only to the origin server. The content is, of interest and relevance only to the origin server. The content is,
in fact, readable by anyone who examines the Set-Cookie header. in fact, readable by anyone who examines the Set-Cookie header.
To maximize compatibility with user agents, servers that wish to To maximize compatibility with user agents, servers that wish to
store non-ASCII data in a cookie-value SHOULD encode that data using store non-ASCII data in a cookie-value SHOULD encode that data using
a printable ASCII encoding, such as base64. a printable ASCII encoding.
NOTE: Some user agents represent dates using 32-bit integers. Some If a server sends multiple responses containing Set-Cookie headers
of these user agents might contain bugs that cause them process dates concurrently to the user agent (e.g., when communicating with the
after the year 2038 incorrectly. Servers wishing to interoperate user agent over multiple sockets), these responses create a "race
with these user agents might wish to use dates before 2038. condition" that can lead to unpredictable behavior.
NOTE: The syntax above allows whitespace around the U+003D ("=") NOTE: Some user agents represent dates using 32-bit UNIX time_t
characters. Servers wishing to interoperate with some legacy user values. Some of these user agents might contain bugs that cause them
agents might wish to omit this whitespace. process dates after the year 2038 incorrectly. Servers wishing to
interoperate with these user agents might wish to use dates before
2038.
4.1.2. Semantics (Non-Normative) 4.1.2. Semantics (Non-Normative)
This section describes a simplified semantics of the Set-Cookie This section describes a simplified semantics of the Set-Cookie
header. These semantics are detailed enough to be useful for header. These semantics are detailed enough to be useful for
understanding the most common uses of cookies. The full semantics understanding the most common uses of cookies. The full semantics
are described in Section 5. are described in Section 5.
When the user agent receives a Set-Cookie header, the user agent When the user agent receives a Set-Cookie header, the user agent
stores the cookie in its cookie store. Subsequently, when the user stores the cookie in its cookie store. Subsequently, when the user
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4.1.2.2. The Max-Age Attribute 4.1.2.2. The Max-Age Attribute
The Max-Age attribute indicates the maximum lifetime of the cookie, The Max-Age attribute indicates the maximum lifetime of the cookie,
represented as the number of seconds until the cookie expires. The represented as the number of seconds until the cookie expires. The
user agent is not required to retain the cookie until the specified user agent is not required to retain the cookie until the specified
date has passed. In fact, user agents often evict cookies from the date has passed. In fact, user agents often evict cookies from the
cookie store due to memory pressure or privacy concerns. cookie store due to memory pressure or privacy concerns.
WARNING: Not all user agents support the Max-Age attribute. User WARNING: Not all user agents support the Max-Age attribute. User
agents that do not support the Max-Age attribute will retain the agents that do not support the Max-Age attribute will ignore the
cookie for the current session only. attribute.
If a cookie has both the Max-Age and the Expires attribute, the Max- If a cookie has both the Max-Age and the Expires attribute, the Max-
Age attribute has precedence and controls the expiration date of the Age attribute has precedence and controls the expiration date of the
cookie. cookie. If a cookie has neither the Max-Age nor the Expires
attribute, the user agent will retain the cookie until "the current
session is over" (as defined by the user agent).
4.1.2.3. The Domain Attribute 4.1.2.3. The Domain Attribute
The Domain attribute specifies those hosts to which the cookie will The Domain attribute specifies those hosts to which the cookie will
be sent. For example, if the Domain attribute contains the value be sent. For example, if the Domain attribute contains the value
"example.com", the user agent will include the cookie in the Cookie "example.com", the user agent will include the cookie in the Cookie
header when making HTTP requests to example.com, www.example.com, and header when making HTTP requests to example.com, www.example.com, and
www.corp.example.com. (Note that a leading U+002E ("."), if present, www.corp.example.com. (Note that a leading U+002E ("."), if present,
is ignored.) If the server omits the Domain attribute, the user is ignored even though that character is not permitted by the
agent will return the cookie only to the origin server. subdomain production in [RFC1034].) If the server omits the Domain
attribute, the user agent will return the cookie only to the origin
server.
WARNING: Some legacy user agents treat an absent Domain attribute WARNING: Some legacy user agents treat an absent Domain attribute
as if the Domain attribute were present and contained the current as if the Domain attribute were present and contained the current
host name. For example, if example.com returns a Set-Cookie host name. For example, if example.com returns a Set-Cookie
header without a Domain attribute, these user agents will header without a Domain attribute, these user agents will
erroneously send the cookie to www.example.com. erroneously send the cookie to www.example.com as well.
The user agent will reject cookies (refuse to store them in the The user agent will reject cookies (refuse to store them in the
cookie store) unless the Domain attribute specifies a scope for the cookie store) unless the Domain attribute specifies a scope for the
cookie that would include the origin server. For example, the user cookie that would include the origin server. For example, the user
agent will accept a Domain attribute of "example.com" or of agent will accept a Domain attribute of "example.com" or of
"foo.example.com" from foo.example.com, but the user agent will not "foo.example.com" from foo.example.com, but the user agent will not
accept a Domain attribute of "bar.example.com" or of accept a Domain attribute of "bar.example.com" or of
"baz.foo.example.com". "baz.foo.example.com".
NOTE: For security reasons, some user agents are configured to reject NOTE: For security reasons, some user agents are configured to reject
Domain attributes that correspond to "public suffixes." For example, Domain attributes that correspond to "public suffixes." For example,
some user agents will reject Domain attributes of "com" or "co.uk". some user agents will reject Domain attributes of "com" or "co.uk".
4.1.2.4. The Path Attribute 4.1.2.4. The Path Attribute
The Path attribute limits the scope of the cookie to a set of paths. The scope of each cookie is limited to a set of paths, controlled by
When a cookie has a Path attribute, the user agent will include the the Path attribute. If the server omits the Path attribute, the user
cookie in an HTTP request only if the path portion of the Request-URI agent will use the directory of the request-uri's path component as
matches (or is a subdirectory of) the cookie's Path attribute, where the default value.
the U+002F ("/") character is interpreted as a directory separator.
If the server omits the Path attribute, the user agent will use the The user agent will include the cookie in an HTTP request only if the
directory of the Request-URI's path component as the default value. path portion of the request-uri matches (or is a subdirectory of) the
cookie's Path attribute, where the U+002F ("/") character is
interpreted as a directory separator.
Although seemingly useful for isolating cookies between different Although seemingly useful for isolating cookies between different
paths within a given domain, the Path attribute cannot be relied upon paths within a given domain, the Path attribute cannot be relied upon
for security for two reasons: for security (see Section 8).
1. User agents do not prevent one path from overwriting the cookies
for another path. For example, if a response to a request for
/foo/bar.html attempts to set a cookie with a Path attribute of
"/baz" the user agent will store that cookie in the cookie store.
2. 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 "same origin".
4.1.2.5. The Secure Attribute 4.1.2.5. The Secure Attribute
The Secure attribute limits the scope of the cookie to "secure" The Secure attribute limits the scope of the cookie to "secure"
channels (where "secure" is defined by the user agent). When a channels (where "secure" is defined by the user agent). When a
cookie has the Secure attribute, the user agent will include the cookie has the Secure attribute, the user agent will include the
cookie in an HTTP request only if the request is transmitted over a cookie in an HTTP request only if the request is transmitted over a
secure channel (typically TLS [RFC5246]). secure channel (typically TLS [RFC5246]).
Although seemingly useful for protecting cookies from active network Although seemingly useful for protecting cookies from active network
attackers, the Secure attribute protects only the cookie's attackers, the Secure attribute protects only the cookie's
confidentiality. An active network attacker can overwrite Secure confidentiality. An active network attacker can overwrite Secure
cookies from an insecure channel, disrupting its integrity. cookies from an insecure channel, disrupting its integrity.
4.1.2.6. The HttpOnly Attribute 4.1.2.6. The HttpOnly Attribute
The HttpOnly attribute limits the scope of the cookie to HTTP The HttpOnly attribute limits the scope of the cookie to HTTP
requests. In particular, the attribute instructs the user agent to requests. In particular, the attribute instructs the user agent to
omit the cookie when providing access to its cookie store via "non- omit the cookie when providing access to its cookie store via "non-
HTTP" APIs (as defined by the user agent). HTTP" APIs (such as HTML's document.cookie API).
4.2. Cookie 4.2. Cookie
4.2.1. Syntax 4.2.1. Syntax
The user agent returns stored cookies to the origin server in the The user agent returns stored cookies to the origin server in the
Cookie header. If the server conforms to the requirements in this Cookie header. If the server conforms to the requirements in
section, the requirements in the next section will cause the user Section 4.1, the requirements in the Section 5 will cause the user
agent to return a Cookie header that conforms to the following agent to return a Cookie header that conforms to the following
grammar: grammar:
cookie-header = "Cookie:" OWS cookie-string OWS cookie-header = "Cookie:" OWS cookie-string OWS
cookie-string = cookie-pair *( ";" cookie-pair ) cookie-string = cookie-pair *( ";" SP cookie-pair )
4.2.2. Semantics 4.2.2. Semantics
Each cookie-pair represents a cookie stored by the user agent. The Each cookie-pair represents a cookie stored by the user agent. The
cookie-name and the cookie-value are returned from the corresponding cookie-name and the cookie-value are returned from the corresponding
parts of the Set-Cookie header. parts of the Set-Cookie header.
Notice that the cookie attributes are not returned. In particular, Notice that the cookie attributes are not returned. In particular,
the server cannot determine from the Cookie header alone when a the server cannot determine from the Cookie header alone when a
cookie will expire, for which domains the cookie is valid, for which 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 paths the cookie is valid, or whether the cookie was set with the
Secure or HttpOnly attributes. Secure or HttpOnly attributes.
The semantics of individual cookies in the Cookie header is not The semantics of individual cookies in the Cookie header is not
defined by this document. Servers are expected to imbue these defined by this document. Servers are expected to imbue these
cookies with application-specific semantics. cookies with application-specific semantics.
Although cookies are serialized linearly in the Cookie header, Although cookies are serialized linearly in the Cookie header,
servers SHOULD NOT rely upon the serialization order. In particular, servers SHOULD NOT rely upon the serialization order. In particular,
if the Cookie header contains two cookies with the same name, servers if the Cookie header contains two cookies with the same name (e.g.,
SHOULD NOT rely upon the order in which these cookies appear in the with different Path or Domain attributes), servers SHOULD NOT rely
header. upon the order in which these cookies appear in the header.
5. User Agent Requirements 5. User Agent Requirements
For historical reasons, the full semantics of cookies contains a For historical reasons, the full semantics of cookies contains a
number of exotic quirks. This section is intended to specify the number of exotic quirks. This section is intended to specify the
Cookie and Set-Cookie headers in sufficient detail to allow a user Cookie and Set-Cookie headers in sufficient detail to allow a user
agent implementing these requirements precisely to interoperate with agent implementing these requirements precisely to interoperate with
existing servers. existing servers.
Conformance requirements phrased as algorithms or specific steps MAY
be implemented in any manner, so long as the end result is
equivalent. In particular, the algorithms defined in this
specification are intended to be easy to understand and are not
intended to be performant.
5.1. Algorithms 5.1. Algorithms
This section defines a number of algorithms used by user agents to This section defines a number of algorithms used by user agents to
process the Cookie and Set-Cookie headers. process the Cookie and Set-Cookie headers.
5.1.1. Dates 5.1.1. Dates
The user agent MUST use the following algorithm to *parse a cookie- The user agent MUST use an algorithm equivalent to the following
date*: algorithm to parse a cookie-date:
1. Using the grammar below, divide the cookie-date into date-tokens. 1. Using the grammar below, divide the cookie-date into date-tokens.
cookie-date = *delimiter date-token-list *delimiter cookie-date = *delimiter date-token-list *delimiter
date-token-list = date-token *( 1*delimiter date-token ) date-token-list = date-token *( 1*delimiter date-token )
delimiter = %x09 / %x20 / %x21 / %x22 / %x23 / %x24 / delimiter = %x09 / %x20 / %x21 / %x22 / %x23 / %x24 /
%x25 / %x26 / %x27 / %x28 / %x29 / %x2A / %x25 / %x26 / %x27 / %x28 / %x29 / %x2A /
%x2B / %x2C / %x2D / %x2E / %x2F / %x3B / %x2B / %x2C / %x2D / %x2E / %x2F / %x3B /
%x3C / %x3D / %x3E / %x3F / %x40 / %x5B / %x3C / %x3D / %x3E / %x3F / %x40 / %x5B /
%x5C / %x5D / %x5E / %x5F / %x60 / %x7B / %x5C / %x5D / %x5E / %x5F / %x60 / %x7B /
%x7C / %x7D / %x7E %x7C / %x7D / %x7E
date-token = day-of-month / month / year / time / mystery date-token = day-of-month / month / year / time / mystery
day-of-month = 2DIGIT / DIGIT day-of-month = 2DIGIT / DIGIT
month = "jan" [ mystery ] / "feb" [ mystery ] / month = "jan" [ mystery ] / "feb" [ mystery ] /
"mar" [ mystery ] / "apr" [ mystery ] / "mar" [ mystery ] / "apr" [ mystery ] /
"may" [ mystery ] / "jun" [ mystery ] / "may" [ mystery ] / "jun" [ mystery ] /
"jul" [ mystery ] / "aug" [ mystery ] / "jul" [ mystery ] / "aug" [ mystery ] /
"sep" [ mystery ] / "oct" [ mystery ] / "sep" [ mystery ] / "oct" [ mystery ] /
"nov" [ mystery ] / "dec" [ mystery ] "nov" [ mystery ] / "dec" [ mystery ]
year = 5DIGIT / 4DIGIT / 3DIGIT / 2DIGIT / DIGIT year = 4DIGIT / 3DIGIT / 2DIGIT / DIGIT
time = time-field ":" time-field ":" time-field time = time-field ":" time-field ":" time-field
time-field = 2DIGIT / DIGIT time-field = 2DIGIT / DIGIT
mystery = <anything except a delimiter> CTLwoHTAB = %x00-08 / %x0A-1F / %x7F
; CTL except HTAB
mystery = CTLwoHTAB / ":" / ALPHA / DIGIT / %x80-FF
; any OCTET except a delimiter
2. Process each date-token sequentially in the order the date-tokens 2. Process each date-token sequentially in the order the date-tokens
appear in the cookie-date: appear in the cookie-date:
1. If the found-day-of-month flag is not set and the date-token 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- matches the day-of-month production, set the found-day-of-
month flag and set the day-of-month-value to the number month flag and set the day-of-month-value to the number
denoted by the date-token. Skip the remaining sub-steps and denoted by the date-token. Skip the remaining sub-steps and
continue to the next date-token. continue to the next date-token.
2. If the found-month flag is not set and the date-token matches 2. If the found-month flag is not set and the date-token matches
skipping to change at page 16, line 29 skipping to change at page 16, line 30
the year production, set the found-year flag and set the the year production, set the found-year flag and set the
year-value to the number denoted by the date-token. Skip the year-value to the number denoted by the date-token. Skip the
remaining sub-steps and continue to the next date-token. remaining sub-steps and continue to the next date-token.
4. If the found-time flag is not set and the token matches the 4. If the found-time flag is not set and the token matches the
time production, set the found-time flag and set the hour- time production, set the found-time flag and set the hour-
value, minute-value, and second-value to the numbers denoted value, minute-value, and second-value to the numbers denoted
by the digits in the date-token, respectively. Skip the by the digits in the date-token, respectively. Skip the
remaining sub-steps and continue to the next date-token. remaining sub-steps and continue to the next date-token.
3. Abort these steps and *fail to parse* if 3. If the year-value is greater than 68 and less than 100, increment
the year-value by 1900.
4. If the year-value is greater than or equal to 0 and less than 69,
increment the year-value by 2000.
5. Abort these steps and fail to parse if
* at least one of the found-day-of-month, found-month, found- * at least one of the found-day-of-month, found-month, found-
year, or found-time flags is not set, year, or found-time flags is not set,
* the day-of-month-value is less than 1 or greater than 31, * the day-of-month-value is less than 1 or greater than 31,
* the year-value is less than 1601 or greater than 30827, * the year-value is less than 1601,
* the hour-value is greater than 23, * the hour-value is greater than 23,
* the minute-value is greater than 59, or * the minute-value is greater than 59, or
* the second-value is greater than 59. * the second-value is greater than 59.
4. If the year-value is greater than 68 and less than 100, increment
the year-value by 1900.
5. If the year-value is greater than or equal to 0 and less than 69,
increment the year-value by 2000.
6. Let the parsed-cookie-date be the date whose day-of-month, month, 6. Let the parsed-cookie-date be the date whose day-of-month, month,
year, hour, minute, and second (in GMT) are the day-of-month- year, hour, minute, and second (in GMT) are the day-of-month-
value, the month-value, the year-value, the hour-value, the value, the month-value, the year-value, the hour-value, the
minute-value, and the second-value, respectively. minute-value, and the second-value, respectively.
7. Return the parsed-cookie-date as the result of this algorithm. 7. Return the parsed-cookie-date as the result of this algorithm.
5.1.2. Domains 5.1.2. Domains
A *canonicalized* host-name is the host-name converted to lower case A canonicalized host-name is the host-name converted to lower case
and expressed in punycode [RFC3492]. and converted to ASCII according to the IDNA specification [RFC3490].
A request-host *domain-matches* a cookie-domain if at least one of A host-name domain-matches a cookie-domain if at least one of the
the following conditions hold: following conditions hold:
o The cookie-domain and the canonicalized request-host are o The cookie-domain and the host-name are identical.
identical.
o All of the following conditions hold: o All of the following conditions hold:
* The cookie-domain is a suffix of the canonicalized request- * The cookie-domain is a suffix of the host-name.
host.
* The last character of the canonicalized request-host that is * The last character of the host-name that is not included in the
not included in the cookie-domain is a U+002E (".") character. cookie-domain is a U+002E (".") character.
* The request-host is a host name (i.e., not an IP address). * The host-name is a host name (i.e., not an IP address).
5.1.3. Paths 5.1.3. Paths
The user agent MUST use the following algorithm to compute the The user agent MUST use an algorithm equivalent to the following
*default-path* of a cookie: algorithm to compute the default-path of a cookie:
1. Let uri-path be the path portion of the Request-URI. 1. Let uri-path be the path portion of the request-uri. That is, if
the request-uri contains just a path (and optional query string),
then the uri-path is that path (without the U+003F ("?")
character or query string), and if the request-uri contains a
full absoluteURI, the uri-path is the abs_path component of that
URI.
2. If the first character of the uri-path is not a U+002F ("/") 2. If the uri-path is empty or if first character of the uri-path is
character, output U+002F ("/") and skip the remaining steps. not a U+002F ("/") character, output U+002F ("/") and skip the
remaining steps.
3. If the uri-path contains only a single U+002F ("/") character, 3. If the uri-path contains only a single U+002F ("/") character,
output U+002F ("/") and skip the remaining steps. output U+002F ("/") and skip the remaining steps.
4. Output the characters of the uri-path from the first character up 4. Output the characters of the uri-path from the first character up
to, but not including, the right-most U+002F ("/"). to, but not including, the right-most U+002F ("/").
A request-path *path-matches* a cookie-path if at least one of the A request-path path-matches a cookie-path if at least one of the
following conditions hold: following conditions hold:
o The cookie-path and the request-path are identical. o The cookie-path and the request-path are identical.
o The cookie-path is a prefix of the request-path and the last o The cookie-path is a prefix of the request-path and the last
character of the cookie-path is U+002F ("/"). character of the cookie-path is U+002F ("/").
o The cookie-path is a prefix of the request-path and the first o The cookie-path is a prefix of the request-path and the first
character of the request-path that is not included in the cookie- character of the request-path that is not included in the cookie-
path is a U+002F ("/") character. path is a U+002F ("/") character.
5.2. The Set-Cookie Header 5.2. The Set-Cookie Header
When a user agent receives a Set-Cookie header in an HTTP response, When a user agent receives a Set-Cookie header in an HTTP response,
the user agent *receives a set-cookie-string* consisting of the value the user agent receives a set-cookie-string consisting of the value
of the header. of the header.
A user agent MUST use the following algorithm to parse set-cookie- A user agent MUST use an algorithm equivalent to the following
strings: algorithm to parse set-cookie-strings:
1. If the set-cookie-string is empty or consists entirely of WSP
characters, ignore the set-cookie-string entirely.
2. If the set-cookie-string contains a U+003B (";") character: 1. If the set-cookie-string contains a U+003B (";") character:
The name-value-pair string consists of the characters up to, The name-value-pair string consists of the characters up to,
but not including, the first U+003B (";"), and the unparsed- but not including, the first U+003B (";"), and the unparsed-
attributes consist of the remainder of the set-cookie-string attributes consist of the remainder of the set-cookie-string
(including the U+003B (";") in question). (including the U+003B (";") in question).
Otherwise: Otherwise:
The name-value-pair string consists of all the characters The name-value-pair string consists of all the characters
contained in the set-cookie-string, and the unparsed- contained in the set-cookie-string, and the unparsed-
attributes is the empty string. attributes is the empty string.
3. If the name-value-pair string lacks a U+003D ("=") character, 2. If the name-value-pair string lacks a U+003D ("=") character,
ignore the set-cookie-string entirely. ignore the set-cookie-string entirely.
4. If the first character of the name-value-pair string is U+003D 3. The (possibly empty) name string consists of the characters up
("="), ignore the set-cookie-string entirely. to, but not including, the first U+003D ("=") character, and the
(possibly empty) value string consists of the characters after
5. The (necessarily non-empty) name string consists of the the first U+003D ("=") character.
characters up to, but not including, the first U+003D ("=")
character, and the (possibly empty) value string consists of the
characters after the first U+003D ("=") character.
6. Remove any leading or trailing WSP characters from the name 4. Remove any leading or trailing WSP characters from the name
string and the value string. string and the value string.
7. The cookie-name is the name string, and the cookie-value is the 5. If the name string is empty, ignore the set-cookie-string
entirely.
6. The cookie-name is the name string, and the cookie-value is the
value string. value string.
The user agent MUST use the following algorithm to parse the The user agent MUST use an algorithm equivalent to the following
unparsed-attributes: algorithm to parse the unparsed-attributes:
1. If the unparsed-attributes string is empty, skip the rest of 1. If the unparsed-attributes string is empty, skip the rest of
these steps. these steps.
2. Consume the first character of the unparsed-attributes (which 2. Discard the first character of the unparsed-attributes (which
will be a U+003B (";") character). will be a U+003B (";") character).
3. If the remaining unparsed-attributes contains a U+003B (";") 3. If the remaining unparsed-attributes contains a U+003B (";")
character: character:
Consume the characters of the unparsed-attributes up to, but Consume the characters of the unparsed-attributes up to, but
not including, the first U+003B (";") character. not including, the first U+003B (";") character.
Otherwise: Otherwise:
skipping to change at page 19, line 43 skipping to change at page 19, line 46
Otherwise: Otherwise:
The attribute-name string consists of the entire cookie-av The attribute-name string consists of the entire cookie-av
string, and the attribute-value string is empty. string, and the attribute-value string is empty.
5. Remove any leading or trailing WSP characters from the attribute- 5. Remove any leading or trailing WSP characters from the attribute-
name string and the attribute-value string. name string and the attribute-value string.
6. Process the attribute-name and attribute-value according to the 6. Process the attribute-name and attribute-value according to the
requirements in the following subsections. requirements in the following subsections. (Notice that
attributes with unrecognizeed attribute-names are ignored.)
7. Return to Step 1. 7. Return to Step 1.
When the user agent finishes parsing the set-cookie-string, the user When the user agent finishes parsing the set-cookie-string, the user
agent *receives a cookie* from the Request-URI with name cookie-name, agent receives a cookie from the request-uri with name cookie-name,
value cookie-value, and attributes cookie-attribute-list. value cookie-value, and attributes cookie-attribute-list.
5.2.1. The Expires Attribute 5.2.1. The Expires Attribute
If the attribute-name case-insensitively matches the string If the attribute-name case-insensitively matches the string
"Expires", the user agent MUST process the cookie-av as follows. "Expires", the user agent MUST process the cookie-av as follows.
Let the parsed-cookie-date be the result of parsing the attribute- Let the parsed-cookie-date be the result of parsing the attribute-
value as cookie-date. value as cookie-date.
skipping to change at page 22, line 28 skipping to change at page 22, line 30
attribute-list with an attribute-name of HttpOnly and an empty attribute-list with an attribute-name of HttpOnly and an empty
attribute-value. attribute-value.
5.3. Storage Model 5.3. Storage Model
The user agent stores the following fields about each cookie: name, The user agent stores the following fields about each cookie: name,
value, expiry-time, domain, path, creation-time, last-access-time, value, expiry-time, domain, path, creation-time, last-access-time,
persistent-flag, host-only-flag, secure-only-flag, and http-only- persistent-flag, host-only-flag, secure-only-flag, and http-only-
flag. flag.
When the user agent *receives a cookie* from a Request-URI with name When the user agent receives a cookie from a request-uri with name
cookie-name, value cookie-value, and attributes cookie-attribute- cookie-name, value cookie-value, and attributes cookie-attribute-
list, the user agent MUST process the cookie as follows: list, the user agent MUST process the cookie as follows:
1. A user agent MAY ignore a received cookie in its entirety. For 1. A user agent MAY ignore a received cookie in its entirety. For
example, the user agent might wish to block receiving cookies example, the user agent might wish to block receiving cookies
from "third-party" responses. from "third-party" responses or the user agent might not wish to
store cookie that exceed some size.
2. Create a new cookie with name cookie-name, value cookie-value. 2. Create a new cookie with name cookie-name, value cookie-value.
Set the creation-time and the last-access-time to the current Set the creation-time and the last-access-time to the current
date and time. date and time.
3. If the cookie-attribute-list contains an attribute with an 3. If the cookie-attribute-list contains an attribute with an
attribute-name of "Max-Age": attribute-name of "Max-Age":
Set the cookie's persistent-flag to true. Set the cookie's persistent-flag to true.
skipping to change at page 23, line 29 skipping to change at page 23, line 31
attribute-name of "Domain": attribute-name of "Domain":
Let the domain-attribute be the attribute-value of the last Let the domain-attribute be the attribute-value of the last
attribute in the cookie-attribute-list with an attribute-name attribute in the cookie-attribute-list with an attribute-name
of "Domain". of "Domain".
Otherwise: Otherwise:
Let the domain-attribute be the empty string. Let the domain-attribute be the empty string.
5. If the user agent is configured to use a "public suffix" list 5. If the user agent is configured to reject "public suffixes" and
and the domain-attribute is a public suffix: the domain-attribute is a public suffix:
If the domain-attribute is identical to the canonicalized If the domain-attribute is identical to the canonicalized
Request-URI's host: request-host:
Let the domain-attribute be the empty string. Let the domain-attribute be the empty string.
Otherwise: Otherwise:
Ignore the cookie entirely and abort these steps Ignore the cookie entirely and abort these steps
NOTE: A "public suffix" is a domain that is controlled by a NOTE: A "public suffix" is a domain that is controlled by a
public registry, such as "com", "co.uk", and "pvt.k12.wy.us". public registry, such as "com", "co.uk", and "pvt.k12.wy.us".
This step is essential for preventing attacker.com from This step is essential for preventing attacker.com from
disrupting the integrity of example.com by setting a cookie disrupting the integrity of example.com by setting a cookie
with a Domain attribute of "com". Unfortunately, the set of with a Domain attribute of "com". Unfortunately, the set of
public suffixes (also known as "registry controlled domains") public suffixes (also known as "registry controlled domains")
changes over time. If feasible, user agents SHOULD use an changes over time. If feasible, user agents SHOULD use an
up-to-date public suffix list, such as the one maintained by up-to-date public suffix list, such as the one maintained by
the Mozilla project at http://publicsuffix.org/. the Mozilla project at http://publicsuffix.org/.
6. If the domain-attribute is non-empty: 6. If the domain-attribute is non-empty:
If the Request-URI's host does not domain-match the domain- If the cannonicalized request-host does not domain-match the
attribute, ignore the cookie entirely and abort these steps. domain-attribute, ignore the cookie entirely and abort these
steps.
Set the cookie's host-only-flag to false. Set the cookie's host-only-flag to false.
Set the cookie's domain to the domain-attribute. Set the cookie's domain to the domain-attribute.
Otherwise: Otherwise:
Set the cookie's host-only-flag to true. Set the cookie's host-only-flag to true.
Set the cookie's domain to the canonicalized host of the Set the cookie's domain to the canonicalized request-host.
Request-URI.
7. If the cookie-attribute-list contains an attribute with an 7. If the cookie-attribute-list contains an attribute with an
attribute-name of "Path", set the cookie's path to attribute- attribute-name of "Path", set the cookie's path to attribute-
value of the last attribute in the cookie-attribute-list with an value of the last attribute in the cookie-attribute-list with an
attribute-name of "Path". Otherwise, set cookie's path to the attribute-name of "Path". Otherwise, set cookie's path to the
default-path of the Request-URI. default-path of the request-uri.
8. If the cookie-attribute-list contains an attribute with an 8. If the cookie-attribute-list contains an attribute with an
attribute-name of "Secure", set the cookie's secure-only-flag to attribute-name of "Secure", set the cookie's secure-only-flag to
true. Otherwise, set cookie's secure-only-flag to false. true. Otherwise, set cookie's secure-only-flag to false.
9. If the cookie-attribute-list contains an attribute with an 9. If the cookie-attribute-list contains an attribute with an
attribute-name of "HttpOnly", set the cookie's http-only-flag to attribute-name of "HttpOnly", set the cookie's http-only-flag to
true. Otherwise, set cookie's http-only-flag to false. true. Otherwise, set cookie's http-only-flag to false.
10. If the cookie's name and value are both empty, abort these steps 10. If the cookie was received from a non-HTTP API and the cookie's
and ignore the cookie entirely.
11. If the cookie was received from a non-HTTP API and the cookie's
http-only-flag is set, abort these steps and ignore the cookie http-only-flag is set, abort these steps and ignore the cookie
entirely. entirely.
12. If the cookie store contains a cookie with the same name, 11. If the cookie store contains a cookie with the same name,
domain, and path as the newly created cookie: domain, and path as the newly created cookie:
1. Let old-cookie be the existing cookie with the same name, 1. Let old-cookie be the existing cookie with the same name,
domain, and path as the newly created cookie. (Notice that domain, and path as the newly created cookie. (Notice that
this algorithm maintains the invariant that there is at most this algorithm maintains the invariant that there is at most
one such cookie.) one such cookie.)
2. If the newly created cookie was received from an non-HTTP 2. If the newly created cookie was received from an non-HTTP
API and the old-cookie's host-only-flag is set, abort these API and the old-cookie's http-only-flag is set, abort these
steps and ignore the newly created cookie entirely. steps and ignore the newly created cookie entirely.
3. Update the creation-time of the newly created cookie to 3. Update the creation-time of the newly created cookie to
match the creation-time of the old-cookie. match the creation-time of the old-cookie.
4. Remove the old-cookie from the cookie store. 4. Remove the old-cookie from the cookie store.
13. Insert the newly created cookie into the cookie store. 12. Insert the newly created cookie into the cookie store.
The user agent MUST evict a cookie from the cookie store if, at any A cookie is "expired" if the cookie has an expiry date in the past.
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 The user agent MUST evict all expired cookies from the cookie store
of cookies sharing a domain field exceeds some predetermined upper if, at any time, an expired cookie exists in the cookie store.
bound (such as 50 cookies).
The user agent MAY evict a cookie from the cookie store if the cookie At any time, the user agent MAY "remove excess cookies" from the
store exceeds some predetermined upper bound (such as 3000 cookies). cookie store if the number of cookies sharing a domain field exceeds
some predetermined upper bound (such as 50 cookies).
When the user agent evicts a cookie from the cookie store, the user At any time, the user agent MAY "remove excess cookies" form the
agent MUST evict cookies in the following priority order: cookie store if the cookie store exceeds some predetermined upper
bound (such as 3000 cookies).
1. Cookies with an expiry date in the past. When the user agent removes excess cookies from the cookie store, the
user agent MUST evict cookies in the following priority order:
1. Expired cookies.
2. Cookies that share a domain field with more than a predetermined 2. Cookies that share a domain field with more than a predetermined
number of other cookies. number of other cookies.
3. All cookies. 3. All cookies.
If two cookies have the same removal priority, the user agent MUST If two cookies have the same removal priority, the user agent MUST
evict the cookie with the least recent last-access date first. evict the cookie with the least recent last-access date first.
When "the current session is over" (as defined by the user agent), When "the current session is over" (as defined by the user agent),
the user agent MUST remove from the cookie store all cookies with the the user agent MUST remove from the cookie store all cookies with the
persistent-flag set to false. persistent-flag set to false.
5.4. The Cookie Header 5.4. The Cookie Header
When the user agent generates an HTTP request, the user agent SHOULD When the user agent generates an HTTP request, the user agent SHOULD
attach exactly one HTTP header named Cookie if the cookie-string attach exactly one HTTP header named Cookie if the cookie-string
(defined below) for the Request-URI is non-empty. (defined below) for the request-uri is non-empty.
A user agent MAY omit the Cookie header in its entirety. For A user agent MAY omit the Cookie header in its entirety. For
example, the user agent might wish to block sending cookies during example, the user agent might wish to block sending cookies during
"third-party" requests. "third-party" requests.
The user agent MUST use the following algorithm to compute the The user agent MUST use an algorithm equivalent to the following
cookie-string from a cookie store and a Request-URI: algorithm to compute the cookie-string from a cookie store and a
request-uri:
1. Let cookie-list be the set of cookies from the cookie store that 1. Let cookie-list be the set of cookies from the cookie store that
meet all of the following requirements: meet all of the following requirements:
* Let request-host be the Request-URI's host. Either: * Either:
The cookie's host-only-flag is true and the canonicalized The cookie's host-only-flag is true and the canonicalized
request-host is identical to the cookie's domain. request-host is identical to the cookie's domain.
Or: Or:
The cookie's host-only-flag is false and the request-host The cookie's host-only-flag is false and the canonicalized
domain-matches cookie's domain. request-host domain-matches cookie's domain.
* The Request-URI's path patch-matches cookie's path. * The request-uri's path path-matches cookie's path.
* If the cookie's secure-only-flag is true, then the Request- * If the cookie's secure-only-flag is true, then the request-
URI's scheme must denote a "secure" protocol (as defined by uri's scheme must denote a "secure" protocol (as defined by
the user agent). the user agent).
NOTE: The notion of a "secure" protocol is not defined by NOTE: The notion of a "secure" protocol is not defined by
this document. Typically, user agents consider a protocol this document. Typically, user agents consider a protocol
secure if the protocol makes use of transport-layer secure if the protocol makes use of transport-layer
security, such as TLS. For example, most user agents security, such as TLS. For example, most user agents
consider "https" to be a scheme that denotes a secure consider "https" to be a scheme that denotes a secure
protocol. protocol.
* If the cookie's http-only-flag is true, then exclude the * If the cookie's http-only-flag is true, then exclude the
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* Cookies with longer paths are listed before cookies with * Cookies with longer paths are listed before cookies with
shorter paths. shorter paths.
* Among cookies that have equal length path fields, cookies with * Among cookies that have equal length path fields, cookies with
earlier creation-times are listed before cookies with later earlier creation-times are listed before cookies with later
creation-times. creation-times.
NOTE: Not all user agents sort the cookie-list in this order, but NOTE: Not all user agents sort the cookie-list in this order, but
this order reflects common practice when this document was this order reflects common practice when this document was
written. The specific ordering might not be optimal in every written, and, historically, there have been servers that
metric, but using the consensus ordering is a relatively low cost (erroneously) depended on this order.
way to improve interoperability between user agents.
3. Update the last-access-time of each cookie in the cookie-list to 3. Update the last-access-time of each cookie in the cookie-list to
the current date and time. the current date and time.
4. Serialize the cookie-list into a cookie-string by processing each 4. Serialize the cookie-list into a cookie-string by processing each
cookie in the cookie-list in order: cookie in the cookie-list in order:
1. Output the cookie's name, the U+003D ("=") character, and the 1. Output the cookie's name, the U+003D ("=") character, and the
cookie's value. cookie's value.
2. If there is an unprocessed cookie in the cookie-list, output 2. If there is an unprocessed cookie in the cookie-list, output
the characters U+003B and U+0020 ("; "). the characters U+003B and U+0020 ("; ").
NOTE: Despite its name, the cookie-string is actually a sequence of NOTE: Despite its name, the cookie-string is actually a sequence of
octets, not a sequence of characters. To convert the cookie-string octets, not a sequence of characters. To convert the cookie-string
into a sequence of characters (e.g., for presentation to the user), (or components thereof) into a sequence of characters (e.g., for
the user agent SHOULD use the UTF-8 character encoding [RFC3629]. presentation to the user), the user agent SHOULD use the UTF-8
character encoding [RFC3629].
6. Implementation Considerations 6. Implementation Considerations
6.1. Limits 6.1. Limits
Practical user agent implementations have limits on the number and Practical user agent implementations have limits on the number and
size of cookies that they can store. General-use user agents SHOULD size of cookies that they can store. General-use user agents SHOULD
provide each of the following minimum capabilities: provide each of the following minimum capabilities:
o At least 4096 bytes per cookie (as measured by the sum of the o At least 4096 bytes per cookie (as measured by the sum of the
length of the cookie's name, value, and attributes). length of the cookie's name, value, and attributes).
o At least 50 cookies per domain. o At least 50 cookies per domain.
o At least 3000 cookies total. o At least 3000 cookies total.
Servers SHOULD use as few and as small cookies as possible to avoid Servers SHOULD use as few and as small cookies as possible to avoid
reaching these implementation limits and to avoid network latency due reaching these implementation limits and to minimize network
to the Cookie header being included in every request. bandwidth due to the Cookie header being included in every request.
Servers should gracefully degrade if the user agent fails to return Servers SHOULD gracefully degrade if the user agent fails to return
one or more cookies in the Cookie header because the user agent might one or more cookies in the Cookie header because the user agent might
evict any cookie at any time on orders from the user. evict any cookie at any time on orders from the user.
6.2. Application Programmer Interfaces 6.2. Application Programmer Interfaces
One reason the Cookie and Set-Cookie headers uses such esoteric One reason the Cookie and Set-Cookie headers uses such esoteric
syntax is because many platforms (both in servers and user agents) syntax is because many platforms (both in servers and user agents)
provide a string-based application programmer interface (API) to provide a string-based application programmer interface (API) to
cookies, requiring application-layer programmers to generate and cookies, requiring application-layer programmers to generate and
parse the syntax used by the Cookie and Set-Cookie headers. parse the syntax used by the Cookie and Set-Cookie headers, which
many programmers have done incorrectly, resulting in interoperability
problems.
Instead of providing string-based APIs to cookies, platforms would be Instead of providing string-based APIs to cookies, platforms would be
well-served by providing more semantic APIs. It is beyond the scope well-served by providing more semantic APIs. It is beyond the scope
of this document to recommend specific API designs, but there are of this document to recommend specific API designs, but there are
clear benefits to accepting a abstract "Date" object instead of a clear benefits to accepting a abstract "Date" object instead of a
serialized date string. serialized date string.
7. Privacy Considerations 7. Privacy Considerations
Cookies are often criticized for letting servers track users. For Cookies are often criticized for letting servers track users. For
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Some user agents provide users with the ability to approve individual Some user agents provide users with the ability to approve individual
writes to the cookie store. In many common usage scenarios, these writes to the cookie store. In many common usage scenarios, these
controls generate a large number of prompts. However, some privacy- controls generate a large number of prompts. However, some privacy-
conscious users find these controls useful nonetheless. conscious users find these controls useful nonetheless.
8. Security Considerations 8. Security Considerations
8.1. Overview 8.1. Overview
Cookies have a number of security and privacy pitfalls. Cookies have a number of security pitfalls. This section overviews a
few of the more salient issues.
In particular, cookies encourage developers to rely on ambient In particular, cookies encourage developers to rely on ambient
authority for authentication, often becoming vulnerable to attacks authority for authentication, often becoming vulnerable to attacks
such as cross-site request forgery. Also, when storing session such as cross-site request forgery. Also, when storing session
identifiers in cookies, developers often create session fixation identifiers in cookies, developers often create session fixation
vulnerabilities. vulnerabilities.
Transport-layer encryption, such as that employed in HTTPS, is Transport-layer encryption, such as that employed in HTTPS, is
insufficient to prevent a network attacker from obtaining or altering insufficient to prevent a network attacker from obtaining or altering
a victim's cookies because the cookie protocol itself has various a victim's cookies because the cookie protocol itself has various
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Cookies do not provide isolation by scheme. Although most commonly Cookies do not provide isolation by scheme. Although most commonly
used with the http and https schemes, the cookies for a given host used with the http and https schemes, the cookies for a given host
might also be available to other schemes, such as ftp and gopher. might also be available to other schemes, such as ftp and gopher.
Although this lack of isolation by scheme is most apparent in via Although this lack of isolation by scheme is most apparent in via
non-HTTP APIs that permit access to cookies (e.g., HTML's non-HTTP APIs that permit access to cookies (e.g., HTML's
document.cookie API), the lack of isolation by scheme is actually document.cookie API), the lack of isolation by scheme is actually
present in requirements for processing cookies themselves (e.g., present in requirements for processing cookies themselves (e.g.,
consider retrieving a URI with the gopher scheme via HTTP). consider retrieving a URI with the gopher scheme via HTTP).
Cookies do not always provide isolation by path. Although the Cookies do not always provide isolation by path. Although the
network-level protocol does not send cookie stored for one path to network-level protocol does not send cookies stored for one path to
another, some user agents expose cookies via non-HTTP APIs, such as another, some user agents expose cookies via non-HTTP APIs, such as
HTML's document.cookie API. Because some of these user agents (e.g., HTML's document.cookie API. Because some of these user agents (e.g.,
web browsers) do not isolate resources received from different paths, web browsers) do not isolate resources received from different paths,
a resource retrieved from one path might be able to access cookies a resource retrieved from one path might be able to access cookies
stored for another path. stored for another path.
8.6. Weak Integrity 8.6. Weak Integrity
Cookies do not provide integrity guarantees for sibling domains (and Cookies do not provide integrity guarantees for sibling domains (and
their subdomains). For example, consider foo.example.com and their subdomains). For example, consider foo.example.com and
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attack against example.com even if example.com uses HTTPS attack against example.com even if example.com uses HTTPS
exclusively. exclusively.
Servers can partially mitigate these attacks by encrypting and Servers can partially mitigate these attacks by encrypting and
signing the contents of their cookies. However, using cryptography signing the contents of their cookies. However, using cryptography
does not mitigate the issue completely because an attacker can replay does not mitigate the issue completely because an attacker can replay
a cookie he or she received from the authentic example.com server in a cookie he or she received from the authentic example.com server in
the user's session, with unpredictable results. the user's session, with unpredictable results.
Finally, an attacker might be able to force the user agent to delete Finally, an attacker might be able to force the user agent to delete
cookies by storing large number of cookies. Once the user agent cookies by storing a large number of cookies. Once the user agent
reaches its storage limit, the user agent will be forced to evict reaches its storage limit, the user agent will be forced to evict
some cookies. Servers SHOULD NOT rely upon user agents retaining some cookies. Servers SHOULD NOT rely upon user agents retaining
cookies. cookies.
8.7. Reliance on DNS 8.7. Reliance on DNS
Cookies rely upon the Domain Name System (DNS) for security. If the Cookies rely upon the Domain Name System (DNS) for security. If the
DNS is partially or fully compromised, the cookie protocol might fail DNS is partially or fully compromised, the cookie protocol might fail
to provide the security properties required by applications. to provide the security properties required by applications.
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
for Internationalized Domain Names in Applications "Internationalizing Domain Names in Applications (IDNA)",
(IDNA)", RFC 3492, March 2003. RFC 3490, March 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003. 10646", STD 63, RFC 3629, November 2003.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
9.2. Informative References 9.2. Informative References
[RFC2109] Kristol, D. and L. Montulli, "HTTP State Management [RFC2109] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2109, February 1997. Mechanism", RFC 2109, February 1997.
[RFC2965] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, October 2000.
Appendix A. Acknowledgements Appendix A. Acknowledgements
This document borrows heavily from RFC 2109 [RFC2109]. We are This document borrows heavily from RFC 2109 [RFC2109]. We are
indebted to David M. Kristol and Lou Montulli for their efforts to indebted to David M. Kristol and Lou Montulli for their efforts to
specify the cookie protocol. David M. Kristol, in particular, specify the cookie protocol. David M. Kristol, in particular,
provided invaluable advice on navigating the IETF process. We would provided invaluable advice on navigating the IETF process. We would
also like to thank Thomas Broyer, Tyler Close, Bil Corry, corvid, also like to thank Thomas Broyer, Tyler Close, Bil Corry, corvid,
Lisa Dusseault, Roy T. Fielding, Blake Frantz, Eran Hammer-Lahav, Lisa Dusseault, Roy T. Fielding, Blake Frantz, Eran Hammer-Lahav,
Jeff Hodges, Achim Hoffmann, Georg Koppen, Dean McNamee, Mark Miller, Jeff Hodges, Achim Hoffmann, Georg Koppen, Dean McNamee, Mark Miller,
Mark Pauley, Yngve N. Pettersen, Julian Reschke, Mark Seaborn, Maciej Mark Pauley, Yngve N. Pettersen, Julian Reschke, Mark Seaborn, Maciej
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