draft-ietf-httpstate-cookie-08.txt   draft-ietf-httpstate-cookie-09.txt 
httpstate A. Barth httpstate A. Barth
Internet-Draft U.C. Berkeley Internet-Draft U.C. Berkeley
Obsoletes: 2109 (if approved) April 23, 2010 Obsoletes: 2109 (if approved) June 5, 2010
Intended status: Standards Track Intended status: Standards Track
Expires: October 25, 2010 Expires: December 7, 2010
HTTP State Management Mechanism HTTP State Management Mechanism
draft-ietf-httpstate-cookie-08 draft-ietf-httpstate-cookie-09
Abstract Abstract
This document defines the HTTP Cookie and Set-Cookie headers. These This document defines the HTTP Cookie and Set-Cookie header fields.
headers can be used by HTTP servers to store state (called cookies) These header fields can be used by HTTP servers to store state
at HTTP user agents, letting the servers maintain a stateful session (called cookies) at HTTP user agents, letting the servers maintain a
over the mostly stateless HTTP protocol. Although cookies have many stateful session over the mostly stateless HTTP protocol. Although
historical infelicities that degrade their security and privacy, the cookies have many historical infelicities that degrade their security
Cookie and Set-Cookie headers are widely used on the Internet. and privacy, the Cookie and Set-Cookie header fields are widely used
on the Internet.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
If you have suggestions for improving this document, please send If you have suggestions for improving this document, please send
email to http-state@ietf.org. Suggestions with test cases are email to <mailto:http-state@ietf.org>. Suggestions with test cases
especially appreciated. https://tools.ietf.org/wg/httpstate/ are especially appreciated. Further Working Group information is
available from <https://tools.ietf.org/wg/httpstate/>
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
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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.
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This Internet-Draft will expire on October 25, 2010. This Internet-Draft will expire on December 7, 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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Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
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. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Conformance Criteria . . . . . . . . . . . . . . . . . . . 6 2.1. Conformance Criteria . . . . . . . . . . . . . . . . . . . 6
2.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6 2.2. Syntax Notation . . . . . . . . . . . . . . . . . . . . . 6
2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 7 2.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 8 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 13 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 . . . . . . . . . . . . . . . . 19
5.2.2. The Max-Age Attribute . . . . . . . . . . . . . . . . 20 5.2.2. The Max-Age Attribute . . . . . . . . . . . . . . . . 20
5.2.3. The Domain Attribute . . . . . . . . . . . . . . . . . 21 5.2.3. The Domain Attribute . . . . . . . . . . . . . . . . . 20
5.2.4. The Path Attribute . . . . . . . . . . . . . . . . . . 21 5.2.4. The Path Attribute . . . . . . . . . . . . . . . . . . 21
5.2.5. The Secure Attribute . . . . . . . . . . . . . . . . . 22 5.2.5. The Secure Attribute . . . . . . . . . . . . . . . . . 21
5.2.6. The HttpOnly Attribute . . . . . . . . . . . . . . . . 22 5.2.6. The HttpOnly Attribute . . . . . . . . . . . . . . . . 21
5.3. Storage Model . . . . . . . . . . . . . . . . . . . . . . 22 5.3. Storage Model . . . . . . . . . . . . . . . . . . . . . . 21
5.4. The Cookie Header . . . . . . . . . . . . . . . . . . . . 25 5.4. The Cookie Header . . . . . . . . . . . . . . . . . . . . 25
6. Implementation Considerations . . . . . . . . . . . . . . . . 28 6. Implementation Considerations . . . . . . . . . . . . . . . . 27
6.1. Limits . . . . . . . . . . . . . . . . . . . . . . . . . . 28 6.1. Limits . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.2. Application Programmer Interfaces . . . . . . . . . . . . 28 6.2. Application Programming Interfaces . . . . . . . . . . . . 27
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 29 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . . 28
7.1. Third-Party Cookies . . . . . . . . . . . . . . . . . . . 29 7.1. Third-Party Cookies . . . . . . . . . . . . . . . . . . . 28
7.2. User Controls . . . . . . . . . . . . . . . . . . . . . . 29 7.2. User Controls . . . . . . . . . . . . . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 31 8. Security Considerations . . . . . . . . . . . . . . . . . . . 30
8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 31 8.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.2. Ambient Authority . . . . . . . . . . . . . . . . . . . . 31 8.2. Ambient Authority . . . . . . . . . . . . . . . . . . . . 30
8.3. Clear Text . . . . . . . . . . . . . . . . . . . . . . . . 32 8.3. Clear Text . . . . . . . . . . . . . . . . . . . . . . . . 31
8.4. Session Identifiers . . . . . . . . . . . . . . . . . . . 32 8.4. Session Identifiers . . . . . . . . . . . . . . . . . . . 31
8.5. Weak Confidentiality . . . . . . . . . . . . . . . . . . . 33 8.5. Weak Confidentiality . . . . . . . . . . . . . . . . . . . 32
8.6. Weak Integrity . . . . . . . . . . . . . . . . . . . . . . 33 8.6. Weak Integrity . . . . . . . . . . . . . . . . . . . . . . 32
8.7. Reliance on DNS . . . . . . . . . . . . . . . . . . . . . 34 8.7. Reliance on DNS . . . . . . . . . . . . . . . . . . . . . 33
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.1. Normative References . . . . . . . . . . . . . . . . . . . 35 9.1. Normative References . . . . . . . . . . . . . . . . . . . 34
9.2. Informative References . . . . . . . . . . . . . . . . . . 35 9.2. Informative References . . . . . . . . . . . . . . . . . . 34
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 36 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 35
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 37 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
This document defines the HTTP Cookie and Set-Cookie headers. Using This document defines the HTTP Cookie and Set-Cookie header fields.
the Set-Cookie header, an HTTP server can store name/value pairs and Using the Set-Cookie header field, an HTTP server can pass name/value
associated metadata (called cookies) at the user agent. When the pairs and associated metadata (called cookies) to a user agent. When
user agent makes subsequent requests to the server, the user agent the user agent makes subsequent requests to the server, the user
uses the metadata to determine whether to return the name/value pairs agent uses the metadata and other information to determine whether to
in the Cookie header. return the name/value pairs 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 return the cookie, the maximum amount of time the user agent should return the cookie, the
servers to which the user agent should return the cookie, and the servers to which the user agent should return the cookie, and the
protocols for which 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 Prior to this document, there were at least three descriptions of
cookies: the so-called "Netscape cookie specification," RFC 2109 cookies: the so-called "Netscape cookie specification" [Netscape],
[RFC2109], and RFC 2965 [RFC2965]. However, none of these documents RFC 2109 [RFC2109], and RFC 2965 [RFC2965]. However, none of these
describe how the Cookie and Set-Cookie headers are actually used on documents describe how the Cookie and Set-Cookie headers are actually
the Internet. By contrast, this document attempts to specify the used on the Internet (see [Kri2001] for historical context). This
syntax and semantics of these headers as they are actually used on document attempts to specify the syntax and semantics of these
the Internet. headers as they are actually used on the Internet.
2. General Nonsense 2. Conventions
2.1. Conformance Criteria 2.1. Conformance Criteria
The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in document are to be "RECOMMENDED", "MAY", and "OPTIONAL" in this 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 Conformance requirements phrased as algorithms or specific steps can
be implemented in any manner, so long as the end result is be implemented in any manner, so long as the end result is
equivalent. In particular, the algorithms defined in this equivalent. In particular, the algorithms defined in this
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(whitespace). (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: whitespace characters MAY appear:
OWS = *( [ obs-fold ] WSP ) OWS = *( [ obs-fold ] WSP )
; "optional" whitespace ; "optional" whitespace
obs-fold = CRLF obs-fold = CRLF
OWS SHOULD either not be produced or be produced as a single SP OWS SHOULD either not be produced or be produced as a single SP
character. Multiple OWS characters that occur within field-content character.
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], Section
1.3).
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 the absoluteURI (http_URL) of the HTTP Request-Line. port) and the absoluteURI (http_URL) of the HTTP Request-Line.
Two sequence of octets are said to case-insensitively match each
other if and only if they are equivalent under the i;ascii-casemap
collation defined in [RFC4790].
3. Overview 3. Overview
We outline here a way for an origin server to send state information This section outlines a way for an origin server to send state
to a user agent and for the user agent to return the state information to a user agent and for the user agent to return the
information to the origin server. state 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.
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
header at all.
Servers MAY return a Set-Cookie response header with any response. Servers can send a Set-Cookie response header with any response. An
An origin server MAY include multiple Set-Cookie header fields in a origin server can include multiple Set-Cookie header fields in a
single response. Gateways that wish to be transparent to cookies single response. Note that folding multiple Set-Cookie header fields
MUST NOT fold multiple Set-Cookie header fields into a single header into a single header field might change the semantics of the header
field. because the U+002C (",") character is used by the Set-Cookie header
in a way that conflicts with such folding.
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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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.
== Server -> User Agent == == Server -> User Agent ==
Set-Cookie: SID=31d4d96e407aad42 Set-Cookie: SID=31d4d96e407aad42
== 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 As shown the next example, the server can store multiple cookies at
example, the server can store a session identifier as well as the the user agent. For example, the server can store a session
user's preferred language by returning two Set-Cookie header fields. identifier as well as the user's preferred language by returning two
Notice that the server uses the Secure and HttpOnly attributes to Set-Cookie header fields. Notice that the server uses the Secure and
provide additional security protections for the more-sensitive HttpOnly attributes to provide additional security protections for
session identifier. the more-sensitive session identifier (see Section 4.1.2.
== 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 an 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: SID=31d4d96e407aad42; 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 ==
Cookie: SID=31d4d96e407aad42 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 esoteric
esoteric semantics. User agents, however, MUST implement the full semantics described in the next section. User agents, however, MUST
semantics to ensure interoperability with servers making use of the implement the full semantics to ensure interoperability with servers
full semantics. making use of the 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 contains the header name Informally, the Set-Cookie response header contains the header name
"Set-Cookie" followed by a ":" and a cookie. Each cookie begins with "Set-Cookie" followed by a ":" and a cookie. Each cookie begins with
a name-value pair, followed by zero or more attribute-value pairs. a name-value pair, followed by zero or more attribute-value pairs.
Servers SHOULD NOT send Set-Cookie headers that fail to conform to Servers SHOULD NOT send Set-Cookie headers that fail to conform to
the following grammar: the following grammar:
set-cookie-header = "Set-Cookie:" SP set-cookie-string set-cookie-header = "Set-Cookie:" SP set-cookie-string
set-cookie-string = cookie-pair *( ";" SP 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, defined in [RFC 2616], Section 2.2>
cookie-av = expires-av / max-age-av / domain-av /
path-av / secure-av / httponly-av /
extension-av
expires-av = "Expires=" sane-cookie-date
sane-cookie-date = <rfc1123-date, as defined in RFC 2616>
max-age-av = "Max-Age=" 1*DIGIT
domain-av = "Domain=" domain-value
domain-value = <subdomain, as defined in RFC 1034>
path-av = "Path=" path-value
path-value = <abs_path, except those containing ";">
secure-av = "Secure"
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 Set-Cookie header fields in the same
response with the same cookie-name.
The cookie-value is opaque to the user agent and MAY be anything the cookie-av = expires-av / max-age-av / domain-av /
origin server chooses to send. "Opaque" implies that the content is path-av / secure-av / httponly-av /
of interest and relevance only to the origin server. The content is, extension-av
in fact, readable by anyone who examines the Set-Cookie header. expires-av = "Expires=" sane-cookie-date
sane-cookie-date = <rfc1123-date, defined in [RFC 2616], Section 3.3.1>
; Note that RFC 2616 uses a different grammatical
; notation than this document (which uses ABNF
; from [RFC5234]).
max-age-av = "Max-Age=" 1*DIGIT
domain-av = "Domain=" domain-value
domain-value = <subdomain, defined in [RFC 1034], Section 3.5>
path-av = "Path=" path-value
path-value = <any CHAR except CTLs or ";">
secure-av = "Secure"
httponly-av = "HttpOnly"
extension-av = <any CHAR except CTLs or ";">
The semantics of the cookie-value are not defined by this document.
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. a printable ASCII encoding.
The portions of the set-cookie-string produced by the cookie-av term
are known as attributes. To maximize compatibility with user agents,
servers SHOULD NOT produce two attributes with the same name in the
same set-cookie-string.
Servers SHOULD NOT include more than one Set-Cookie header fields in
the same response with the same cookie-name.
If a server sends multiple responses containing Set-Cookie headers If a server sends multiple responses containing Set-Cookie headers
concurrently to the user agent (e.g., when communicating with the concurrently to the user agent (e.g., when communicating with the
user agent over multiple sockets), these responses create a "race user agent over multiple sockets), these responses create a "race
condition" that can lead to unpredictable behavior. condition" that can lead to unpredictable behavior.
NOTE: Some user agents represent dates using 32-bit UNIX time_t NOTE: Some user agents represent dates using 32-bit UNIX time_t
values. Some of these user agents might contain bugs that cause them values. Some of these user agents might contain bugs that cause them
process dates after the year 2038 incorrectly. Servers wishing to process dates after the year 2038 incorrectly. Servers wishing to
interoperate with these user agents might wish to use dates before interoperate with these user agents might wish to use dates before
2038. 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. Subsequently, when the user agent makes an HTTP
agent makes an HTTP request, the user agent consults its cookie store request, the user agent includes the applicable, non-expired cookies
and includes the applicable, non-expired cookies in the Cookie in the Cookie header.
header.
If the user agent receives a new cookie with the same cookie-name, If the user agent receives a new cookie with the same cookie-name,
domain-value, and path-value as a cookie that already exists in its domain-value, and path-value as a cookie that it has already stored,
cookie store, the existing cookie is evicted from the cookie store the existing cookie is evicted and replaced with the new cookie.
and replaced with the new cookie. Notice that servers can delete Notice that servers can delete cookies by sending the user agent a
cookies by sending the user agent a new cookie with an Expires new cookie with an Expires attribute with a value in the past.
attribute with a value in the past.
Unless the cookie's attributes indicate otherwise, the cookie is Unless the cookie's attributes indicate otherwise, the cookie is
returned only to the origin server, and it expires at the end of the returned only to the origin server, and it expires at the end of the
current session (as defined by the user agent). User agents ignore current session (as defined by the user agent). User agents ignore
unrecognized cookie attributes. unrecognized cookie attributes.
4.1.2.1. The Expires Attribute 4.1.2.1. The Expires Attribute
The Expires attribute indicates the maximum lifetime of the cookie, The Expires attribute indicates the maximum lifetime of the cookie,
represented as the date and time at which the cookie expires. The represented as the date and time at which 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 due to
cookie store due to memory pressure or privacy concerns. memory pressure or privacy concerns.
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 for the specified
date has passed. In fact, user agents often evict cookies from the duration. In fact, user agents often evict cookies from due to
cookie store due to memory pressure or privacy concerns. memory pressure or privacy concerns.
WARNING: Not all user agents support the Max-Age attribute. User NOTE: Some legacy user agents do not support the Max-Age
agents that do not support the Max-Age attribute will ignore the attribute. User agents that do not support the Max-Age attribute
attribute. ignore the 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. If a cookie has neither the Max-Age nor the Expires cookie. If a cookie has neither the Max-Age nor the Expires
attribute, the user agent will retain the cookie until "the current attribute, the user agent will retain the cookie until "the current
session is over" (as defined by the user agent). 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 value of the Domain attribute is
"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 even though that character is not permitted by the is ignored even though that character is not permitted.) If the
subdomain production in [RFC1034].) If the server omits the Domain server omits the Domain attribute, the user agent will return the
attribute, the user agent will return the cookie only to the origin cookie only to the origin server.
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 as well. 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 unless the Domain attribute
cookie store) unless the Domain attribute specifies a scope for the specifies a scope for the cookie that would include the origin
cookie that would include the origin server. For example, the user server. For example, the user agent will accept a cookie with a
agent will accept a Domain attribute of "example.com" or of Domain attribute of "example.com" or of "foo.example.com" from
"foo.example.com" from foo.example.com, but the user agent will not foo.example.com, but the user agent will not accept a cookie with a
accept a Domain attribute of "bar.example.com" or of 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, many 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 scope of each cookie is limited to a set of paths, controlled by The scope of each cookie is limited to a set of paths, controlled by
the Path attribute. If the server omits the Path attribute, the user the Path attribute. If the server omits the Path attribute, the user
agent will use the directory of the request-uri's path component as agent will use the "directory" of the request-uri's path component as
the default value. the default value. (See Section 5.1.3 for more details.)
The user agent will include the cookie in an HTTP request only if the The user agent will include the cookie in an HTTP request only if the
path portion of the request-uri matches (or is a subdirectory of) the path portion of the request-uri matches (or is a subdirectory of) the
cookie's Path attribute, where the U+002F ("/") character is cookie's Path attribute, where the U+002F ("/") character is
interpreted as a directory separator. 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 (see Section 8). for security (see Section 8).
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 HTTP over SSL, HTTP over TLS [RFC2818], and
TLS [RFC5246] itself).
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 their 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 cookies via "non-HTTP" APIs
HTTP" APIs (such as HTML's document.cookie API). (such as a web browser API that exposes cookies to scripts).
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 sends stored cookies to the origin server in the
Cookie header. If the server conforms to the requirements in Cookie header. If the server conforms to the requirements in
Section 4.1, the requirements in the Section 5 will cause the user Section 4.1 (and the user agent conforms to the requirements in the
agent to return a Cookie header that conforms to the following Section 5), the user agent will send a Cookie header that conforms to
grammar: the following grammar:
cookie-header = "Cookie:" OWS cookie-string OWS cookie-header = "Cookie:" OWS cookie-string OWS
cookie-string = cookie-pair *( ";" SP 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 are 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 (e.g., if the Cookie header contains two cookies with the same name (e.g.,
with different Path or Domain attributes), servers SHOULD NOT rely with different Path or Domain attributes), servers SHOULD NOT rely
upon the order in which these cookies appear in the 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 contain 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.
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 an algorithm equivalent to the following The user agent MUST use an algorithm equivalent to the following
algorithm to parse a cookie-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 / %x20-2F / %x3B-40 / %x5B-60 / %x7B-7E
%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 date-token = day-of-month / month / year / time / mystery
day-of-month = 2DIGIT / DIGIT day-of-month = 1*2DIGIT
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 = 4DIGIT / 3DIGIT / 2DIGIT / DIGIT year = 1*4DIGIT
time = time-field ":" time-field ":" time-field time = time-field ":" time-field ":" time-field
time-field = 2DIGIT / DIGIT time-field = 1*2DIGIT
CTLwoHTAB = %x00-08 / %x0A-1F / %x7F CTLwoHTAB = %x00-08 / %x0A-1F / %x7F
; CTL except HTAB ; CTL except HTAB
mystery = CTLwoHTAB / ":" / ALPHA / DIGIT / %x80-FF mystery = CTLwoHTAB / ":" / ALPHA / DIGIT / %x80-FF
; any OCTET except a delimiter ; 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-
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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. If the year-value is greater than 68 and less than 100, increment 3. If the year-value is greater than 68 and less than 100, increment
the year-value by 1900. the year-value by 1900.
4. If the year-value is greater than or equal to 0 and less than 69, 4. If the year-value is greater than or equal to 0 and less than 69,
increment the year-value by 2000. increment the year-value by 2000.
5. Abort these steps and fail to parse if 5. Abort these steps and fail to parse the cookie-date 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, * 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.
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. If no such
date exists, abort these steps and fail to parse the cookie-date.
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 string is the string converted to lower case and
and converted to ASCII according to the IDNA specification [RFC3490]. converted to ASCII according to the IDNA specification [RFC3490].
A host-name domain-matches a cookie-domain if at least one of the A string domain-matches a cookie-domain if at least one of the
following conditions hold: following conditions hold:
o The cookie-domain and the host-name are identical. o The cookie-domain and the string are identical.
o All of the following conditions hold: o All of the following conditions hold:
* The cookie-domain is a suffix of the host-name. * The cookie-domain is a suffix of the string.
* The last character of the host-name that is not included in the * The last character of the string that is not included in the
cookie-domain is a U+002E (".") character. cookie-domain is a U+002E (".") character.
* The host-name is a host name (i.e., not an IP address). * The string is a host name (i.e., not an IP address).
5.1.3. Paths 5.1.3. Paths
The user agent MUST use an algorithm equivalent to the following The user agent MUST use an algorithm equivalent to the following
algorithm to compute the 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. That is, if 1. Let uri-path be the path portion of the request-uri if such a
the request-uri contains just a path (and optional query string), portion exists (and empty otherwise). For example, if the
request-uri contains just a path (and optional query string),
then the uri-path is that path (without the U+003F ("?") then the uri-path is that path (without the U+003F ("?")
character or query string), and if the request-uri contains a character or query string), and if the request-uri contains a
full absoluteURI, the uri-path is the abs_path component of that full absoluteURI, the uri-path is the path component of that URI.
URI.
2. If the uri-path is empty or if first character of the uri-path is 2. If the uri-path is empty or if first character of the uri-path is
not a U+002F ("/") character, output U+002F ("/") and skip the not a U+002F ("/") character, output U+002F ("/") and skip the
remaining steps. 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 ("/").
skipping to change at page 18, line 19 skipping to change at page 18, line 11
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 field in an HTTP
the user agent receives a set-cookie-string consisting of the value response, the user agent receives a set-cookie-string consisting of
of the header. the contents of the header field.
A user agent MUST use an algorithm equivalent to the following A user agent MUST use an algorithm equivalent to the following
algorithm to parse set-cookie-strings: algorithm to parse set-cookie-strings:
1. 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).
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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. (Notice that requirements in the following subsections. (Notice that
attributes with unrecognizeed attribute-names are ignored.) attributes with unrecognized 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 expiry-time be the result of parsing the attribute-value as
value as cookie-date. cookie-date (see Section 5.1.1).
If the attribute-value failed to parse as a cookie date, ignore the If the attribute-value failed to parse as a cookie date, ignore the
cookie-av. cookie-av.
If the user agent received the set-cookie-string from an HTTP
response that contains a Date header field and the contents of the
last Date header field successfully parse as a cookie-date:
Let server-date be the date obtained by parsing the contents of
the last Date header field as a cookie-date.
Let delta-seconds be the number of seconds between the server-date
and the parsed-cookie-date (i.e., parsed-cookie-date - server-
date).
Let the expiry-time be the current date and time plus delta-
seconds seconds.
Otherwise:
Let the expiry-time be the parsed-cookie-date.
If the expiry-time is later than the last date the user agent can 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 represent, the user agent MAY replace the expiry-time with the last
representable date. representable date.
If the expiry-time is earlier than the first date the user agent can If the expiry-time is earlier than the earliest date the user agent
represent, the user agent MAY replace the expiry-time with the first can represent, the user agent MAY replace the expiry-time with the
representable date. earliest representable date.
Append an attribute to the cookie-attribute-list with an attribute- Append an attribute to the cookie-attribute-list with an attribute-
name of Expires and an attribute-value of expiry-time. name of Expires and an attribute-value of expiry-time.
5.2.2. The Max-Age Attribute 5.2.2. The Max-Age Attribute
If the attribute-name case-insensitively matches the string "Max- If the attribute-name case-insensitively matches the string "Max-
Age", the user agent MUST process the cookie-av as follows. Age", the user agent MUST process the cookie-av as follows.
If the first character of the attribute-value is not a DIGIT or a "-" If the first character of the attribute-value is not a DIGIT or a "-"
skipping to change at page 22, line 37 skipping to change at page 22, line 8
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 or the user agent might not wish to from "third-party" responses or the user agent might not wish to
store cookie that exceed some size. store cookies 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.
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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 cannonicalized request-host does not domain-match the If the canonicalized request-host does not domain-match the
domain-attribute, ignore the cookie entirely and abort these domain-attribute, ignore the cookie entirely and abort these
steps. 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.
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A cookie is "expired" if the cookie has an expiry date in the past. A cookie is "expired" if the cookie has an expiry date in the past.
The user agent MUST evict all expired cookies from the cookie store The user agent MUST evict all expired cookies from the cookie store
if, at any time, an expired cookie exists in the cookie store. if, at any time, an expired cookie exists in the cookie store.
At any time, the user agent MAY "remove excess cookies" from the At any time, the user agent MAY "remove excess cookies" from the
cookie store if the number of cookies sharing a domain field exceeds cookie store if the number of cookies sharing a domain field exceeds
some predetermined upper bound (such as 50 cookies). some predetermined upper bound (such as 50 cookies).
At any time, the user agent MAY "remove excess cookies" form the At any time, the user agent MAY "remove excess cookies" from the
cookie store if the cookie store exceeds some predetermined upper cookie store if the cookie store exceeds some predetermined upper
bound (such as 3000 cookies). bound (such as 3000 cookies).
When the user agent removes excess cookies from the cookie store, the When the user agent removes excess cookies from the cookie store, the
user agent MUST evict cookies in the following priority order: user agent MUST evict cookies in the following priority order:
1. Expired cookies. 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 earliest 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.
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* The request-uri's path path-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 SSL or TLS. For example, most user
consider "https" to be a scheme that denotes a secure agents consider "https" to be a scheme that denotes a
protocol. secure 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
cookie unless the cookie-string is being generated for an cookie unless the cookie-string is being generated for an
"HTTP" API (as defined by the user agent). "HTTP" API (as defined by the user agent).
2. The user agent SHOULD sort the cookie-list in the following 2. The user agent SHOULD sort the cookie-list in the following
order: order:
* Cookies with longer paths are listed before cookies with * Cookies with longer paths are listed before cookies with
shorter paths. shorter paths.
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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 minimize network reaching these implementation limits and to minimize network
bandwidth due 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 Programming 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, which parse the syntax used by the Cookie and Set-Cookie headers, which
many programmers have done incorrectly, resulting in interoperability many programmers have done incorrectly, resulting in interoperability
problems. 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 an 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
example, a number of "web analytics" companies use cookies to example, a number of "web analytics" companies use cookies to
recognize when a user returns to a web site or visits another web recognize when a user returns to a web site or visits another web
site. Although cookies are not the only mechanism servers can use to site. Although cookies are not the only mechanism servers can use to
track users across HTTP requests, cookies facilitate tracking because track users across HTTP requests, cookies facilitate tracking because
they are persistent across user agent sessions and can be shared they are persistent across user agent sessions and can be shared
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7.1. Third-Party Cookies 7.1. Third-Party Cookies
Particularly worrisome are so-called "third-party" cookies. In Particularly worrisome are so-called "third-party" cookies. In
rendering an HTML document, a user agent often requests resources rendering an HTML document, a user agent often requests resources
from other servers (such as advertising networks). These third-party from other servers (such as advertising networks). These third-party
servers can use cookies to track the user even if the user never servers can use cookies to track the user even if the user never
visits the server directly. visits the server directly.
Some user agents restrict how third-party cookies behave. For Some user agents restrict how third-party cookies behave. For
example, some user agents refuse to send the Cookie header in third- example, some of these user agents refuse to send the Cookie header
party requests. Other user agents refuse to process the Set-Cookie in third-party requests. Others refuse to process the Set-Cookie
header in responses to third-party requests. User agents vary widely header in responses to third-party requests. User agents vary widely
in their third-party cookie policies. This document grants user in their third-party cookie policies. This document grants user
agents wide latitude to experiment with third-party cookie policies agents wide latitude to experiment with third-party cookie policies
that balance the privacy and compatibility needs of their users. that balance the privacy and compatibility needs of their users.
However, this document does not endorse any particular third-party However, this document does not endorse any particular third-party
cookie policy. cookie policy.
Third-party cookie blocking policies are often ineffective at Third-party cookie blocking policies are often ineffective at
achieving their privacy goals if servers attempt to work around their achieving their privacy goals if servers attempt to work around their
restrictions to track users. In particular, two collaborating restrictions to track users. In particular, two collaborating
servers can often track users without using cookies at all. servers can often track users without using cookies at all.
7.2. User Controls 7.2. User Controls
User agents SHOULD provide users with a mechanism for managing the User agents should provide users with a mechanism for managing the
cookies stored in the cookie store. For example, a user agent might cookies stored in the cookie store. For example, a user agent might
let users delete all cookies received during a specified time period let users delete all cookies received during a specified time period
or all the cookies related to a particular domain. In addition, many or all the cookies related to a particular domain. In addition, many
user agent include a user interface element that lets users examine user agent include a user interface element that lets users examine
the cookies stored in their cookie store. the cookies stored in their cookie store.
User agents SHOULD provide users with a mechanism for disabling User agents should provide users with a mechanism for disabling
cookies. When cookies are disabled, the user agent MUST NOT include cookies. When cookies are disabled, the user agent MUST NOT include
a Cookie header in outbound HTTP requests and the user agent MUST NOT a Cookie header in outbound HTTP requests and the user agent MUST NOT
process Set-Cookie headers in inbound HTTP responses. process Set-Cookie headers in inbound HTTP responses.
Some user agents provide users the option of preventing persistent Some user agents provide users the option of preventing persistent
storage of cookies across sessions. When configured thusly, user storage of cookies across sessions. When configured thusly, user
agents MUST treat all received cookies as if the persistent-flag were agents MUST treat all received cookies as if the persistent-flag were
set to false. set to false.
Some user agents provide users with the ability to approve individual Some user agents provide users with the ability to approve individual
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might supply the authorization for a resource designated by the might supply the authorization for a resource designated by the
attacker, possibly causing the server or its clients to undertake attacker, possibly causing the server or its clients to undertake
actions designated by the attacker as though they were authorized by actions designated by the attacker as though they were authorized by
the user. the user.
Instead of using cookies for authorization, server operators might Instead of using cookies for authorization, server operators might
wish to consider entangling designation and authorization by treating wish to consider entangling designation and authorization by treating
URLs as capabilities. Instead of storing secrets in cookies, this URLs as capabilities. Instead of storing secrets in cookies, this
approach stores secrets in URLs, requiring the remote entity to approach stores secrets in URLs, requiring the remote entity to
supply the secret itself. Although this approach is not a panacea, supply the secret itself. Although this approach is not a panacea,
judicious use of these principles can lead to more robust security. judicious application of these principles can lead to more robust
security.
8.3. Clear Text 8.3. Clear Text
Unless sent over a secure channel (such as TLS), the information in Unless sent over a secure channel (such as TLS), the information in
the Cookie and Set-Cookie headers is transmitted in the clear. the Cookie and Set-Cookie headers is transmitted in the clear.
1. All sensitive information conveyed in these headers is exposed to 1. All sensitive information conveyed in these headers is exposed to
an eavesdropper. an eavesdropper.
2. A malicious intermediary could alter the headers as they travel 2. A malicious intermediary could alter the headers as they travel
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transmitting them to the user agent (even when sending the cookies transmitting them to the user agent (even when sending the cookies
over a secure channel). However, encrypting and signing cookie over a secure channel). However, encrypting and signing cookie
contents does not prevent an attacker from transplanting a cookie contents does not prevent an attacker from transplanting a cookie
from one user agent to another or from replaying the cookie at a from one user agent to another or from replaying the cookie at a
later time. later time.
In addition to encrypting and signing the contents of every cookie, In addition to encrypting and signing the contents of every cookie,
servers that require a higher level of security SHOULD use the Cookie servers that require a higher level of security SHOULD use the Cookie
and Set-Cookie headers only over a secure channel. When using and Set-Cookie headers only over a secure channel. When using
cookies over a secure channel, servers SHOULD set the Secure cookies over a secure channel, servers SHOULD set the Secure
attribute for every cookie. If a server does not set the Secure attribute (see Section 4.1.2.5) for every cookie. If a server does
attribute, the protection provided by the secure channel will be not set the Secure attribute, the protection provided by the secure
largely moot. channel will be largely moot.
8.4. Session Identifiers 8.4. Session Identifiers
Instead of storing session information directly in a cookie (where it Instead of storing session information directly in a cookie (where it
might be exposed to or replayed by an attacker), servers commonly might be exposed to or replayed by an attacker), servers commonly
store a nonce (or "session identifier") in a cookie. When the server store a nonce (or "session identifier") in a cookie. When the server
receives an HTTP request with a nonce, the server can look up state receives an HTTP request with a nonce, the server can look up state
information associated with the cookie using the nonce as a key. information associated with the cookie using the nonce as a key.
Using session identifier cookies limits the damage an attacker can Using session identifier cookies limits the damage an attacker can
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service running on another port of the same server. If a cookie is service running on another port of the same server. If a cookie is
writable by a service on one port, the cookie is also writable by a writable by a service on one port, the cookie is also writable by a
service running on another port of the same server. For this reason, service running on another port of the same server. For this reason,
servers SHOULD NOT both run mutually distrusting services on servers SHOULD NOT both run mutually distrusting services on
different ports of the same host and use cookies to store security- different ports of the same host and use cookies to store security-
sensitive information. sensitive information.
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 non-
non-HTTP APIs that permit access to cookies (e.g., HTML's HTTP APIs that permit access to cookies (e.g., HTML's document.cookie
document.cookie API), the lack of isolation by scheme is actually API), the lack of isolation by scheme is actually present in
present in requirements for processing cookies themselves (e.g., requirements for processing cookies themselves (e.g., consider
consider retrieving a URI with the gopher scheme via HTTP). 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 cookies 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
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able to leverage this ability to mount an attack against able to leverage this ability to mount an attack against
bar.example.com. bar.example.com.
Even though the Set-Cookie header supports the Path attribute, the Even though the Set-Cookie header supports the Path attribute, the
Path attribute does not provide any integrity protection because the Path attribute does not provide any integrity protection because the
user agent will accept an arbitrary Path attribute in a Set-Cookie user agent will accept an arbitrary Path attribute in a Set-Cookie
header. For example, an HTTP response to a request for header. For example, an HTTP response to a request for
http://example.com/foo/bar can set a cookie with a Path attribute of http://example.com/foo/bar can set a cookie with a Path attribute of
"/qux". Consequently, servers SHOULD NOT both run mutually "/qux". Consequently, servers SHOULD NOT both run mutually
distrusting services on different paths of the same host and use distrusting services on different paths of the same host and use
cookies store security-sensitive information. cookies to store security-sensitive information.
An active network attacker can also inject cookies into the Cookie An active network attacker can also inject cookies into the Cookie
header sent to https://example.com/ by impersonating a response from header sent to https://example.com/ by impersonating a response from
http://example.com/ and injecting a Set-Cookie header. The HTTPS http://example.com/ and injecting a Set-Cookie header. The HTTPS
server at example.com will be unable to distinguish these cookies server at example.com will be unable to distinguish these cookies
from cookies that it set itself in an HTTPS response. An active from cookies that it set itself in an HTTPS response. An active
network attacker might be able to leverage this ability to mount an network attacker might be able to leverage this ability to mount an
attack against example.com even if example.com uses HTTPS attack against example.com even if example.com uses HTTPS
exclusively. exclusively.
skipping to change at page 35, line 26 skipping to change at page 34, line 26
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.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, [RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)", "Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, 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.
[RFC4790] Newman, C., Duerst, M., and A. Gulbrandsen, "Internet
Application Protocol Collation Registry", RFC 4790,
March 2007.
[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 [RFC2965] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, October 2000. Mechanism", RFC 2965, October 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[Netscape]
"Persistent Client State -- HTTP Cookies".
[Kri2001] Kristol, D., "HTTP Cookies: Standards, Privacy, and
Politics", ACM Transactions on Internet Technology Vol. 1,
#2, November 2001, <http://arxiv.org/abs/cs.SE/0105018>.
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, Bjoern Hoehrmann, Achim Hoffmann, Georg Koppen, Dean
Mark Pauley, Yngve N. Pettersen, Julian Reschke, Mark Seaborn, Maciej McNamee, Mark Miller, Mark Pauley, Yngve N. Pettersen, Julian
Stachowiak, Daniel Stenberg, David Wagner, Dan Winship, and Dan Witte Reschke, Peter Saint-Andre, Mark Seaborn, Maciej Stachowiak, Daniel
for their valuable feedback on this document. Stenberg, David Wagner, Dan Winship, and Dan Witte for their valuable
feedback on this document.
Author's Address Author's Address
Adam Barth Adam Barth
University of California, Berkeley University of California, Berkeley
Email: abarth@eecs.berkeley.edu Email: abarth@eecs.berkeley.edu
URI: http://www.adambarth.com/ URI: http://www.adambarth.com/
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