HTTP State Management Mechanism
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
This document specifies a way to create a stateful session with HTTP requests and responses. It describes two new headers, Cookie and Set-Cookie, which carry state information between participating origin servers and user agents. The method described here differs from Netscape's Cookie proposal, but it can interoperate with HTTP/1.0 user agents that use Netscape's method. (See the HISTORICAL section.)
- The terms user agent, client, server, proxy, and origin server have - the same meaning as in the HTTP/1.0 specification. + The terms user agent, client, server, proxy, origin server, and + http_URL have the same meaning as in the HTTP/1.1 specification + [RFC2616]. The terms abs_path and absoluteURI have the same meaning + as in the URI Syntax specification [RFC2396]. - Fully-qualified host name (FQHN) means either the fully-qualified - domain name (FQDN) of a host (i.e., a completely specified domain - name ending in a top-level domain such as .com or .uk), or the - numeric Internet Protocol (IP) address of a host. The fully - qualified domain name is preferred; use of numeric IP addresses is - strongly discouraged. + Host name (HN) means either the host domain name (HDN) or the numeric + Internet Protocol (IP) address of a host. The fully qualified domain + name is preferred; use of numeric IP addresses is strongly + discouraged. The terms request-host and request-URI refer to the values the client would send to the server as, respectively, the host (but not port) and abs_path portions of the absoluteURI (http_URL) of the HTTP - request line. Note that request-host must be a FQHN. + request line. Note that request-host is a HN. - Hosts names can be specified either as an IP address or a FQHN - string. Sometimes we compare one host name with another. Host A's - name domain-matches host B's if + The term effective host name is related to host name. If a host name + contains no dots, the effective host name is that name with the + string .local appended to it. Otherwise the effective host name is + the same as the host name. Note that all effective host names + contain at least one dot. - * both host names are IP addresses and their host name strings match - exactly; or + The term request-port refers to the port portion of the absoluteURI + (http_URL) of the HTTP request line. If the absoluteURI has no + explicit port, the request-port is the HTTP default, 80. The + request-port of a cookie is the request-port of the request in which + a Set-Cookie2 response header was returned to the user agent. - * both host names are FQDN strings and their host name strings match - exactly; or + Host names can be specified either as an IP address or a HDN string. + Sometimes we compare one host name with another. (Such comparisons + SHALL be case-insensitive.) Host A's name domain-matches host B's if - * A is a FQDN string and has the form NB, where N is a non-empty name - string, B has the form .B', and B' is a FQDN string. (So, x.y.com - domain-matches .y.com but not y.com.) + * their host name strings string-compare equal; or + + * A is a HDN string and has the form NB, where N is a non-empty + name string, B has the form .B', and B' is a HDN string. (So, + x.y.com domain-matches .Y.com but not Y.com.) Note that domain-match is not a commutative operation: a.b.c.com domain-matches .c.com, but not the reverse. + The reach R of a host name H is defined as follows: + + * If + + - H is the host domain name of a host; and, + + - H has the form A.B; and + + - A has no embedded (that is, interior) dots; and + + - B has at least one embedded dot, or B is the string "local". + then the reach of H is .B. + + * Otherwise, the reach of H is H. + + For two strings that represent paths, P1 and P2, P1 path-matches P2 + if P2 is a prefix of P1 (including the case where P1 and P2 string- + compare equal). Thus, the string /tec/waldo path-matches /tec.
Because it was used in Netscape's original implementation of state management, we will use the term cookie to refer to the state information that passes between an origin server and user agent, and that gets stored by the user agent.
This document describes a way to create stateful sessions with HTTP requests and responses. Currently, HTTP servers respond to each client request without relating that request to previous or subsequent requests;
the techniqueallows clients and servers that wish to exchange state information to place HTTP requests and responses within a larger context, which we term a "session". This context might be used to create, for example, a "shopping cart", in which user selections can be aggregated before purchase, or a magazine browsing system, in which a user's previous reading affects which offerings are presented.
この文書は HTTP の要求と応答で状態を持ったセッションを作る方法を説明します。
There are, of course, many different potential contexts and thus many different potential types of session. The designers' paradigm for sessions created by the exchange of cookies has these key attributes:
- Each session has a beginning and an end.
- Each session is relatively short-lived.
- Either the user agent or the origin server may terminate a session.
- The session is implicit in the exchange of state information.
- We outline here a way for an origin server to send state information + We describe here a way for an origin server to send state information to the user agent, and for the user agent to return the state information to the origin server. The goal is to have a minimal + impact on HTTP and user agents. - impact on HTTP and user agents. Only origin servers that need to - maintain sessions would suffer any significant impact, and that - impact can largely be confined to Common Gateway Interface (CGI) - programs, unless the server provides more sophisticated state - management support. (See Implementation Considerations, below.)
The two state management headers, Set-Cookie and Cookie, have common syntactic properties involving attribute-value pairs. The following grammar uses the notation, and tokens DIGIT (decimal digits)
andtoken (informally, a sequence of non-special, non-white space characters) from the HTTP/1.1 specification [RFC 2068]to describe their syntax.
- av-pairs = av-pair *(";" av-pair)
- av-pair = attr ["=" value] ; optional value
- attr = token
value = word word = token | quoted-string
Attributes (names) (attr) are case-insensitive. White space is permitted between tokens. Note that while the above syntax description shows value as optional, most attrs require them.
NOTE: The syntax above allows whitespace between the attribute and the = sign.
The origin server initiates a session, if it so desires.
(Note that "session" here does not refer to a persistent network connection but to a logical session created from HTTP requests and responses. The presence or absence of a persistent connection should have no effect on the use of cookie-derived sessions).To initiate a session, the origin serverreturns an extra response header to the client, Set-Cookie. (The details follow later.)
A user agent returns a Cookie request header (see below) to the origin server if it chooses to continue a session. The origin server
mayignore it or use it to determine the current state of the session. It maysend back to the client a Set-Cookieresponse header with the same or different information, or it maysend no Set-Cookieheader at all. The origin server effectively ends a session by sending the client a Set-Cookieheader with Max-Age=0.
Cookie 要求頭 (後述) を返します。起源鯖はこれを無視しても構いませんし、
mayreturn a Set-Cookieresponse headers with any response. User agents shouldsend Cookie request headers, subject to other rules detailed below, with every request.
An origin server
mayinclude multiple Set-Cookieheaders in a response. Note that an intervening gateway could fold multiple such headers into a single header.
The syntax for the
Set-Cookieresponse header is
set-cookie = "Set-Cookie:" cookies
- cookies = 1#cookie
- cookie = NAME "=" VALUE *(";"
- NAME = attr
- VALUE = value
cookie-av= "Comment" "=" value | "Domain" "=" value | "Max-Age" "=" value | "Path" "=" value | "Secure" | "Version" "=" 1*DIGIT
Set-Cookieresponse header comprises the token Set-Cookie, followed by a comma-separated list of one or more cookies. Each cookie begins with a NAME=VALUE pair, followed by zero or more semi-colon-separated attribute-value pairs. The syntax for attribute-value pairs was shown earlier. The specific attributes and the semantics of their values follows. The NAME=VALUE attribute-value pair mustcome first in each cookie. The others, if present, can occur in any order. If an attribute appears more than once in a cookie, the behavior is undefined.
Required. The name of the state information ("cookie") is NAME, and its value is VALUE. NAMEs that begin with $ are reserved for other usesand must notbe used by applications.
The VALUE is opaque to the user agent and may be anything the origin server chooses to send, possibly in a server-selected printable ASCII encoding. "Opaque" implies that the content is of interest and relevance only to the origin server. The content may, in fact, be readable by anyone that examines the
domain Optional. The Domain attribute specifies the domain for which the cookie is valid. An explicitly specified domain must always start with a dot.
delta-seconds Optional. The Max-Age attribute defines the lifetime of the cookie, in seconds. The delta-seconds value isa decimal non-negative integer. After delta-seconds seconds elapse,the client shoulddiscard the cookie. A value of zero means the cookie shouldbe discarded immediately.
cookieの寿命を秒数 (非負十進整数) で指定します。 齢が
delta-seconds秒よりも大きければ、 クライアントはその cookie を捨てるべきです。 値が零であればその cookie を直ぐに捨てるべきであることを表します。
path Optional. The Path attribute specifies the subset of URLs to which this cookie applies.
Optional. The Secure attribute (with no value) directs the user agent to use only (unspecified) secure means to contact the origin server whenever it sends back this cookie.
The user agent (possibly
under the user's control) maydetermine what level of security it considers appropriate for "secure" cookies. The Secure attribute should be considered security advice from the server to the user agent, indicating that it is in the session's interest to protect the cookie contents.
version Required. The Version attribute, a decimal integer, identifies to whichversion of the state management specification the cookie conforms. For this specification, Version=1 applies.
An origin server must be cognizant of the effect of possible caching - of both the returned resource and the Set-Cookie header. + of both the returned resource and the Set-Cookie2 header. Caching "public" documents is desirable. For example, if the origin server wants to use a public document such as a "front door" page as a sentinel to indicate the beginning of a session for which a - Set-Cookie response header must be generated, the page should + Set-Cookie2 response header must be generated, the page SHOULD be stored in caches "pre-expired" so that the origin server will see further requests. "Private documents", for example those - that contain information strictly private to a session, should not + that contain information strictly private to a session, SHOULD NOT be cached in shared caches. - If the cookie is intended for use by a single user, the Set-cookie + If the cookie is intended for use by a single user, the Set-Cookie2 - header should not be cached. A Set-cookie header that is intended + header SHOULD NOT be cached. A Set-Cookie2 header that is intended - to be shared by multiple users may be cached. + to be shared by multiple users MAY be cached. - The origin server should send the following additional HTTP/1.1 + The origin server SHOULD send the following additional HTTP/1.1 response headers, depending on circumstances: - * To suppress caching of the Set-Cookie header: Cache-control: no- + * To suppress caching of the Set-Cookie2 header: - cache="set-cookie". + Cache-control: no-cache="set-cookie2" and one of the following: - * To suppress caching of a private document in shared caches: Cache- - control: private. + * To suppress caching of a private document in shared caches: + + Cache-control: private * To allow caching of a document and require that it be validated - before returning it to the client: Cache-control: must-revalidate. + before returning it to the client: - * To allow caching of a document, but to require that proxy caches - (not user agent caches) validate it before returning it to the - client: Cache-control: proxy-revalidate. + Cache-Control: must-revalidate, max-age=0 + + * To allow caching of a document, but to require that proxy + caches (not user agent caches) validate it before returning it + to the client: + + Cache-Control: proxy-revalidate, max-age=0 * To allow caching of a document and request that it be validated before returning it to the client (by "pre-expiring" it): - Cache-control: max-age=0. Not all caches will revalidate the - document in every case. - HTTP/1.1 servers must send Expires: old-date (where old-date is a - date long in the past) on responses containing Set-Cookie response + Cache-control: max-age=0 + + Not all caches will revalidate the document in every case. + + HTTP/1.1 servers MUST send Expires: old-date (where old-date is a + date long in the past) on responses containing Set-Cookie2 response headers unless they know for certain (by out of band means) that - there are no downsteam HTTP/1.0 proxies. HTTP/1.1 servers may send - other Cache-Control directives that permit caching by HTTP/1.1 - proxies in addition to the Expires: old-date directive; the Cache- - Control directive will override the Expires: old-date for HTTP/1.1 - proxies. + there are no HTTP/1.0 proxies in the response chain. HTTP/1.1 + servers MAY send other Cache-Control directives that permit caching + by HTTP/1.1 proxies in addition to the Expires: old-date directive; + the Cache-Control directive will override the Expires: old-date for + HTTP/1.1 proxies.
- The user agent keeps separate track of state information that arrives - via Set-Cookie response headers from each origin server (as - distinguished by name or IP address and port). The user agent - applies these defaults for optional attributes that are missing: + The user agent keeps separate track + of state information that arrives via Set-Cookie2 response headers + from each origin server (as distinguished by name or IP address and + port). The user agent MUST ignore attribute-value pairs whose + attribute it does not recognize. The user agent applies these + defaults for optional attributes that are missing: - VersionDefaults to "old cookie" behavior as originally specified by - Netscape. See the HISTORICAL section. + Discard The default behavior is dictated by the presence or absence + of a Max-Age attribute. - Domain Defaults to the request-host. (Note that there is no dot at - the beginning of request-host.) + Domain Defaults to the effective request-host. (Note that because + there is no dot at the beginning of effective request-host, + the default Domain can only domain-match itself.) Max-AgeThe default behavior is to discard the cookie when the user agent exits. Path Defaults to the path of the request URL that generated the - Set-Cookie response, up to, but not including, the - right-most /. + Set-Cookie2 response, up to and including the right-most /. - Secure If absent, the user agent may send the cookie over an + + Port The default behavior is that a cookie MAY be returned to any + request-port. + + Secure If absent, the user agent MAY send the cookie over an insecure channel. ]PRE]
- To prevent possible security or privacy violations, a user agent - rejects a cookie (shall not store its information) if any of the - following is true: + To prevent possible security or privacy + violations, a user agent rejects a cookie according to rules below. + The goal of the rules is to try to limit the set of servers for which + a cookie is valid, based on the values of the Path, Domain, and Port + attributes and the request-URI, request-host and request-port. + A user agent rejects (SHALL NOT store its information) if the Version + attribute is missing. Moreover, a user agent rejects (SHALL NOT + store its information) if any of the following is true of the + attributes explicitly present in the Set-Cookie2 response header: - * The value for the Path attribute is not a prefix of the request- - URI. + * The value for the Path attribute is not a prefix of the + request-URI. - * The value for the Domain attribute contains no embedded dots or - does not start with a dot. + * The value for the Domain attribute contains no embedded dots, + and the value is not .local. - * The value for the request-host does not domain-match the Domain - attribute. + * The effective host name that derives from the request-host does + not domain-match the Domain attribute. - * The request-host is a FQDN (not IP address) and has the form HD, + * The request-host is a HDN (not IP address) and has the form HD, where D is the value of the Domain attribute, and H is a string that contains one or more dots. + * The Port attribute has a "port-list", and the request-port was + not in the list. + Examples: - * A Set-Cookie from request-host y.x.foo.com for Domain=.foo.com + * A Set-Cookie2 from request-host y.x.foo.com for Domain=.foo.com would be rejected, because H is y.x and contains a dot. - * A Set-Cookie from request-host x.foo.com for Domain=.foo.com would - be accepted. + * A Set-Cookie2 from request-host x.foo.com for Domain=.foo.com + would be accepted. - * A Set-Cookie with Domain=.com or Domain=.com., will always be + * A Set-Cookie2 with Domain=.com or Domain=.com., will always be rejected, because there is no embedded dot. - * A Set-Cookie with Domain=ajax.com will be rejected because the - value for Domain does not begin with a dot. + * A Set-Cookie2 with Domain=ajax.com will be accepted, and the + value for Domain will be taken to be .ajax.com, because a dot + gets prepended to the value. + * A Set-Cookie2 with Port="80,8000" will be accepted if the + request was made to port 80 or 8000 and will be rejected + otherwise. + * A Set-Cookie2 from request-host example for Domain=.local will + be accepted, because the effective host name for the request- + host is example.local, and example.local domain-matches .local.
-4.3.3 Cookie Management - If a user agent receives a Set-Cookie response header whose NAME is - the same as a pre-existing cookie, and whose Domain and Path - attribute values exactly (string) match those of a pre-existing - cookie, the new cookie supersedes the old. However, if the Set- - Cookie has a value for Max-Age of zero, the (old and new) cookie is - discarded. Otherwise cookies accumulate until they expire (resources - permitting), at which time they are discarded. + + 3.3.3 Cookie Management If a user agent receives a Set-Cookie2 + response header whose NAME is the same as that of a cookie it has + previously stored, the new cookie supersedes the old when: the old + and new Domain attribute values compare equal, using a case- + insensitive string-compare; and, the old and new Path attribute + values string-compare equal (case-sensitive). However, if the Set- + Cookie2 has a value for Max-Age of zero, the (old and new) cookie is + discarded. Otherwise a cookie persists (resources permitting) until + whichever happens first, then gets discarded: its Max-Age lifetime is + exceeded; or, if the Discard attribute is set, the user agent + terminates the session. Because user agents have finite space in which to store cookies, they - may also discard older cookies to make space for newer ones, using, + MAY also discard older cookies to make space for newer ones, using, for example, a least-recently-used algorithm, along with constraints on the maximum number of cookies that each origin server may set. - If a Set-Cookie response header includes a Comment attribute, the - user agent should store that information in a human-readable form - with the cookie and should display the comment text as part of a + If a Set-Cookie2 response header includes a Comment attribute, the + user agent SHOULD store that information in a human-readable form + with the cookie and SHOULD display the comment text as part of a cookie inspection user interface. - User agents should allow the user to control cookie destruction. An - infrequently-used cookie may function as a "preferences file" for - network applications, and a user may wish to keep it even if it is - the least-recently-used cookie. One possible implementation would be - an interface that allows the permanent storage of a cookie through a - checkbox (or, conversely, its immediate destruction). + If a Set-Cookie2 response header includes a CommentURL attribute, the + user agent SHOULD store that information in a human-readable form + with the cookie, or, preferably, SHOULD allow the user to follow the + http_URL link as part of a cookie inspection user interface. + + The cookie inspection user interface may include a facility whereby a + user can decide, at the time the user agent receives the Set-Cookie2 + response header, whether or not to accept the cookie. A potentially + confusing situation could arise if the following sequence occurs: + + * the user agent receives a cookie that contains a CommentURL + attribute; + + * the user agent's cookie inspection interface is configured so + that it presents a dialog to the user before the user agent + accepts the cookie; + + + + + * the dialog allows the user to follow the CommentURL link when + the user agent receives the cookie; and, + + * when the user follows the CommentURL link, the origin server + (or another server, via other links in the returned content) + returns another cookie. + + The user agent SHOULD NOT send any cookies in this context. The user + agent MAY discard any cookie it receives in this context that the + user has not, through some user agent mechanism, deemed acceptable. + + User agents SHOULD allow the user to control cookie destruction, but + they MUST NOT extend the cookie's lifetime beyond that controlled by + the Discard and Max-Age attributes. An infrequently-used cookie may + function as a "preferences file" for network applications, and a user + may wish to keep it even if it is the least-recently-used cookie. One + possible implementation would be an interface that allows the + permanent storage of a cookie through a checkbox (or, conversely, its + immediate destruction). Privacy considerations dictate that the user have considerable control over cookie management. The PRIVACY section contains more information. -4.3.4 Sending Cookies to the Origin Server - - When it sends a request to an origin server, the user agent sends a - Cookie request header to the origin server if it has cookies that are - applicable to the request, based on + 3.3.4 Sending Cookies to the Origin Server When it sends a request + to an origin server, the user agent includes a Cookie request header + if it has stored cookies that are applicable to the request, based on - * the request-host; + * the request-host and request-port; * the request-URI; * the cookie's age. The syntax for the header is: - cookie = "Cookie:" cookie-version - 1*((";" | ",") cookie-value) - cookie-value = NAME "=" VALUE [";" path] [";" domain] +cookie = "Cookie:" cookie-version 1*((";" | ",") cookie-value) +cookie-value = NAME "=" VALUE [";" path] [";" domain] [";" port] cookie-version = "$Version" "=" value NAME = attr VALUE = value path = "$Path" "=" value domain = "$Domain" "=" value +port = "$Port" [ "=" <"> value <"> ] - The value of the cookie-version attribute must be the value from the - Version attribute, if any, of the corresponding Set-Cookie response - header. Otherwise the value for cookie-version is 0. The value for - the path attribute must be the value from the Path attribute, if any, - of the corresponding Set-Cookie response header. Otherwise the - attribute should be omitted from the Cookie request header. The - value for the domain attribute must be the value from the Domain - attribute, if any, of the corresponding Set-Cookie response header. - Otherwise the attribute should be omitted from the Cookie request - header. + The value of the cookie-version attribute MUST be the value from the + Version attribute of the corresponding Set-Cookie2 response header. + Otherwise the value for cookie-version is 0. The value for the path + attribute MUST be the value from the Path attribute, if one was + present, of the corresponding Set-Cookie2 response header. Otherwise + the attribute SHOULD be omitted from the Cookie request header. The + value for the domain attribute MUST be the value from the Domain + attribute, if one was present, of the corresponding Set-Cookie2 + response header. Otherwise the attribute SHOULD be omitted from the + Cookie request header. - Note that there is no Comment attribute in the Cookie request header - corresponding to the one in the Set-Cookie response header. The user - agent does not return the comment information to the origin server. + The port attribute of the Cookie request header MUST mirror the Port + attribute, if one was present, in the corresponding Set-Cookie2 + response header. That is, the port attribute MUST be present if the + Port attribute was present in the Set-Cookie2 header, and it MUST + have the same value, if any. Otherwise, if the Port attribute was + absent from the Set-Cookie2 header, the attribute likewise MUST be + omitted from the Cookie request header. - The following rules apply to choosing applicable cookie-values from - among all the cookies the user agent has. + Note that there is neither a Comment nor a CommentURL attribute in + the Cookie request header corresponding to the ones in the Set- + Cookie2 response header. The user agent does not return the comment + information to the origin server. - Domain Selection - The origin server's fully-qualified host name must domain-match - the Domain attribute of the cookie. + The user agent applies the following rules to choose applicable + cookie-values to send in Cookie request headers from among all the + cookies it has received. - Path Selection - The Path attribute of the cookie must match a prefix of the - request-URI. + Domain Selection + The origin server's effective host name MUST domain-match the + Domain attribute of the cookie. - Max-Age Selection - Cookies that have expired should have been discarded and thus - are not forwarded to an origin server. + Port Selection + There are three possible behaviors, depending on the Port + attribute in the Set-Cookie2 response header: + 1. By default (no Port attribute), the cookie MAY be sent to any + port. + 2. If the attribute is present but has no value (e.g., Port), the + cookie MUST only be sent to the request-port it was received + from. + 3. If the attribute has a port-list, the cookie MUST only be + returned if the new request-port is one of those listed in + port-list. + Path Selection + The request-URI MUST path-match the Path attribute of the cookie. + Max-Age Selection + Cookies that have expired should have been discarded and thus are + not forwarded to an origin server. If multiple cookies satisfy the criteria above, they are ordered in the Cookie header such that those with more specific Path attributes precede those with less specific. Ordering with respect to other attributes (e.g., Domain) is unspecified. Note: For backward compatibility, the separator in the Cookie header - is semi-colon (;) everywhere. A server should also accept comma (,) + is semi-colon (;) everywhere. A server SHOULD also accept comma (,) as the separator between cookie-values for future compatibility. + 3.3.5 Identifying What Version is Understood: Cookie2 The Cookie2 + request header facilitates interoperation between clients and servers + that understand different versions of the cookie specification. When + the client sends one or more cookies to an origin server, if at least + one of those cookies contains a $Version attribute whose value is + different from the version that the client understands, then the + client MUST also send a Cookie2 request header, the syntax for which + is + + cookie2 = "Cookie2:" cookie-version + + Here the value for cookie-version is the highest version of cookie + specification (currently 1) that the client understands. The client + needs to send at most one such request header per request. -4.3.5 Sending Cookies in Unverifiable Transactions + 3.3.6 Sending Cookies in Unverifiable Transactions Users MUST have + control over sessions in order to ensure privacy. (See PRIVACY + section below.) To simplify implementation and to prevent an + additional layer of complexity where adequate safeguards exist, + however, this document distinguishes between transactions that are + verifiable and those that are unverifiable. A transaction is + verifiable if the user, or a user-designated agent, has the option to + review the request-URI prior to its use in the transaction. A + transaction is unverifiable if the user does not have that option. + Unverifiable transactions typically arise when a user agent + automatically requests inlined or embedded entities or when it + resolves redirection (3xx) responses from an origin server. + Typically the origin transaction, the transaction that the user + initiates, is verifiable, and that transaction may directly or + indirectly induce the user agent to make unverifiable transactions. - Users must have control over sessions in order to ensure privacy. - (See PRIVACY section below.) To simplify implementation and to - prevent an additional layer of complexity where adequate safeguards - exist, however, this document distinguishes between transactions that - are verifiable and those that are unverifiable. A transaction is - verifiable if the user has the option to review the request-URI prior - to its use in the transaction. A transaction is unverifiable if the - user does not have that option. Unverifiable transactions typically - arise when a user agent automatically requests inlined or embedded - entities or when it resolves redirection (3xx) responses from an - origin server. Typically the origin transaction, the transaction - that the user initiates, is verifiable, and that transaction may - directly or indirectly induce the user agent to make unverifiable - transactions. + An unverifiable transaction is to a third-party host if its request- + host U does not domain-match the reach R of the request-host O in the + origin transaction. - When it makes an unverifiable transaction, a user agent must enable a - session only if a cookie with a domain attribute D was sent or - received in its origin transaction, such that the host name in the - Request-URI of the unverifiable transaction domain-matches D. + + When it makes an unverifiable transaction, a user agent MUST disable + all cookie processing (i.e., MUST NOT send cookies, and MUST NOT + accept any received cookies) if the transaction is to a third-party + host. This restriction prevents a malicious service author from using unverifiable transactions to induce a user agent to start or continue a session with a server in a different domain. The starting or continuation of such sessions could be contrary to the privacy expectations of the user, and could also be a security problem. - User agents may offer configurable options that allow the user agent, + User agents MAY offer configurable options that allow the user agent, or any autonomous programs that the user agent executes, to ignore the above rule, so long as these override options default to "off". + (N.B. Mechanisms may be proposed that will automate overriding the + third-party restrictions under controlled conditions.) + Many current user agents already provide a review option that would render many links verifiable. For instance, some user agents display the URL that would be referenced for a particular link when the mouse pointer is placed over that link. The user can therefore determine whether to visit that site before causing the browser to do so. (Though not implemented on current user agents, a similar technique could be used for a button used to submit a form -- the user agent could display the action to be taken if the user were to select that button.) However, even this would not make all links verifiable; for example, links to automatically loaded images would not normally be subject to "mouse pointer" verification. Many user agents also provide the option for a user to view the HTML source of a document, or to save the source to an external file where it can be viewed by another application. While such an option does provide a crude review mechanism, some users might not consider it acceptable for this purpose. -4.4 How an Origin Server Interprets the Cookie Header +3.4 How an Origin Server Interprets the Cookie Header - A user agent returns much of the information in the Set-Cookie + A user agent returns much of the information in the Set-Cookie2 header to the origin server when - the Path attribute matches that of a new request. + the request-URI path-matches the Path attribute of the cookie. - When it receives a Cookie header, the origin server should + When it receives a Cookie header, the origin server SHOULD treat cookies with NAMEs whose prefix is $ specially, as an attribute for the + cookie. - adjacent cookie. The value for such a NAME is to be interpreted as applying to the lexically (left-to-right) most recent - cookie whose name does not have the $ prefix. If there is no - previous cookie, the value applies to the cookie mechanism as a - whole. For example, consider the cookie - Cookie: $Version="1"; Customer="WILE_E_COYOTE"; - $Path="/acme" - $Version applies to the cookie mechanism as a whole (and gives the - version number for the cookie mechanism). $Path is an attribute - whose value (/acme) defines the Path attribute that was used when the - Customer cookie was defined in a Set-Cookie response header. -4.5 Caching Proxy Role +3.5 Caching Proxy Role One reason for separating state information from both a URL and document content is to facilitate the scaling that caching permits. - To support cookies, a caching proxy must obey these rules already in + To support cookies, a caching proxy MUST obey these rules already in the HTTP specification: > * Honor requests from the cache, if possible, based on cache validity rules. > * Pass along a Cookie request header in any request that the proxy proxy must make of another server. - * Return the response to the client. Include any Set-Cookie + * Return the response to the client. Include any Set-Cookie2 response header. > * Cache the received response subject to the control of the usual + headers, such as Expires, - headers, such as Expires, Cache-control: no-cache, and Cache- - control: private, + Cache-control: no-cache + and + Cache-control: private + * Cache the Set-Cookie2 subject to the control of the usual + header, + Cache-control: no-cache="set-cookie2" - * Cache the Set-Cookie subject to the control of the usual header, - Cache-control: no-cache="set-cookie". (The Set-Cookie header - should usually not be cached.) + (The Set-Cookie2 header should usually not be cached.) - Proxies must not introduce Set-Cookie (Cookie) headers of their own + Proxies MUST NOT introduce Set-Cookie2 (Cookie) headers of their own in proxy responses (requests).
-5.1 Example 1 +4.1 Example 1 Most detail of request and response headers has been omitted. Assume the user agent has no stored cookies. 1. User Agent -> Server POST /acme/login HTTP/1.1 [form data] User identifies self via a form. 2. Server -> User Agent HTTP/1.1 200 OK - Set-Cookie: Customer="WILE_E_COYOTE"; Version="1"; Path="/acme" + Set-Cookie2: Customer="WILE_E_COYOTE"; Version="1"; Path="/acme" Cookie reflects user's identity. 3. User Agent -> Server POST /acme/pickitem HTTP/1.1 Cookie: $Version="1"; Customer="WILE_E_COYOTE"; $Path="/acme" [form data] User selects an item for "shopping basket". 4. Server -> User Agent HTTP/1.1 200 OK - Set-Cookie: Part_Number="Rocket_Launcher_0001"; Version="1"; + Set-Cookie2: Part_Number="Rocket_Launcher_0001"; Version="1"; Path="/acme" Shopping basket contains an item. 5. User Agent -> Server POST /acme/shipping HTTP/1.1 Cookie: $Version="1"; Customer="WILE_E_COYOTE"; $Path="/acme"; Part_Number="Rocket_Launcher_0001"; $Path="/acme" [form data] User selects shipping method from form. 6. Server -> User Agent HTTP/1.1 200 OK - Set-Cookie: Shipping="FedEx"; Version="1"; Path="/acme" + Set-Cookie2: Shipping="FedEx"; Version="1"; Path="/acme" New cookie reflects shipping method. 7. User Agent -> Server POST /acme/process HTTP/1.1 Cookie: $Version="1"; Customer="WILE_E_COYOTE"; $Path="/acme"; Part_Number="Rocket_Launcher_0001"; $Path="/acme"; Shipping="FedEx"; $Path="/acme" [form data] User chooses to process order. 8. Server -> User Agent HTTP/1.1 200 OK Transaction is complete. The user agent makes a series of requests on the origin server, after each of which it receives a new cookie. All the cookies have the - same Path attribute and (default) domain. Because the request URLs + same Path attribute and (default) domain. Because the request-URIs - all have /acme as a prefix, and that matches the Path attribute, each + all path-match /acme, the Path attribute of each cookie, each request - request contains all the cookies received so far. + contains all the cookies received so far. -5.2 Example 2 +4.2 Example 2 This example illustrates the effect of the Path attribute. All detail of request and response headers has been omitted. Assume the user agent has no stored cookies. Imagine the user agent has received, in response to earlier requests, the response headers - Set-Cookie: Part_Number="Rocket_Launcher_0001"; Version="1"; + Set-Cookie2: Part_Number="Rocket_Launcher_0001"; Version="1"; Path="/acme" and - Set-Cookie: Part_Number="Riding_Rocket_0023"; Version="1"; + Set-Cookie2: Part_Number="Riding_Rocket_0023"; Version="1"; Path="/acme/ammo" A subsequent request by the user agent to the (same) server for URLs of the form /acme/ammo/... would include the following request header: Cookie: $Version="1"; Part_Number="Riding_Rocket_0023"; $Path="/acme/ammo"; Part_Number="Rocket_Launcher_0001"; $Path="/acme" Note that the NAME=VALUE pair for the cookie with the more specific Path attribute, /acme/ammo, comes before the one with the less specific Path attribute, /acme. Further note that the same cookie name appears more than once. A subsequent request by the user agent to the (same) server for a URL of the form /acme/parts/ would include the following request header: Cookie: $Version="1"; Part_Number="Rocket_Launcher_0001"; $Path="/acme" Here, the second cookie's Path attribute /acme/ammo is not a prefix of the request URL, /acme/parts/, so the cookie does not get forwarded to the server.
- Here we speculate on likely or desirable details for an origin server + Here we provide guidance on likely or desirable details for an origin - that implements state management. + server that implements state management. -6.1 Set-Cookie Content +5.1 Set-Cookie2 Content An origin server's content should probably be divided into disjoint application areas, some of which require the use of state information. The application areas can be distinguished by their - request URLs. The Set-Cookie header can incorporate information + request URLs. The Set-Cookie2 header can incorporate information about the application areas by setting the Path attribute for each one. The session information can obviously be clear or encoded text that describes state. However, if it grows too large, it can become unwieldy. Therefore, an implementor might choose for the session information to be a key to a server-side resource. Of course, using a database creates some problems that this state management specification was meant to avoid, namely: 1. keeping real state on the server side; 2. how and when to garbage-collect the database entry, in case the user agent terminates the session by, for example, exiting. -6.2 Stateless Pages +5.2 Stateless Pages Caching benefits the scalability of WWW. Therefore it is important to reduce the number of documents that have state embedded in them inherently. For example, if a shopping-basket-style application always displays a user's current basket contents on each page, those pages cannot be cached, because each user's basket's contents would be different. On the other hand, if each page contains just a link that allows the user to "Look at My Shopping Basket", the page can be cached. -6.3 Implementation Limits +5.3 Implementation Limits Practical user agent implementations have limits on the number and size of cookies that they can store. In general, user agents' cookie support should have no fixed limits. They should strive to store as many frequently-used cookies as possible. Furthermore, general-use - user agents should provide each of the following minimum capabilities + user agents SHOULD provide each of the following minimum capabilities individually, although not necessarily simultaneously: * at least 300 cookies - * at least 4096 bytes per cookie (as measured by the size of the - characters that comprise the cookie non-terminal in the syntax - description of the Set-Cookie header) + * at least 4096 bytes per cookie (as measured by the characters + that comprise the cookie non-terminal in the syntax description + of the Set-Cookie2 header, and as received in the Set-Cookie2 + header) * at least 20 cookies per unique host or domain name User agents created for specific purposes or for limited-capacity - devices should provide at least 20 cookies of 4096 bytes, to ensure + devices SHOULD provide at least 20 cookies of 4096 bytes, to ensure that the user can interact with a session-based origin server. - The information in a Set-Cookie response header must be retained in + The information in a Set-Cookie2 response header MUST be retained in its entirety. If for some reason there is inadequate space to store - the cookie, it must be discarded, not truncated. + the cookie, it MUST be discarded, not truncated. Applications should use as few and as small cookies as possible, and they should cope gracefully with the loss of a cookie. -6.3.1 Denial of Service Attacks + 5.3.1 Denial of Service Attacks User agents MAY choose to set an + upper bound on the number of cookies to be stored from a given host + or domain name or on the size of the cookie information. Otherwise a + malicious server could attempt to flood a user agent with many + cookies, or large cookies, on successive responses, which would force + out cookies the user agent had received from other servers. However, + the minima specified above SHOULD still be supported. - User agents may choose to set an upper bound on the number of cookies - to be stored from a given host or domain name or on the size of the - cookie information. Otherwise a malicious server could attempt to - flood a user agent with many cookies, or large cookies, on successive - responses, which would force out cookies the user agent had received - from other servers. However, the minima specified above should still - be supported.
onlyset a Path for cookies that are related to the request-URI. -8.2 Cookie Spoofing +7.2 Cookie Spoofing Proper application design can avoid spoofing attacks from related domains. Consider: 1. User agent makes request to victim.cracker.edu, gets back cookie session_id="1234" and sets the default domain victim.cracker.edu. - 2. User agent makes request to spoof.cracker.edu, gets back - cookie session-id="1111", with Domain=".cracker.edu". + 2. User agent makes request to spoof.cracker.edu, gets back cookie + session-id="1111", with Domain=".cracker.edu". 3. User agent makes request to victim.cracker.edu again, and passes - Cookie: $Version="1"; - session_id="1234"; - session_id="1111"; $Domain=".cracker.edu" + Cookie: $Version="1"; session_id="1234", + $Version="1"; session_id="1111"; $Domain=".cracker.edu" The server at victim.cracker.edu should detect that the second cookie was not one it originated by noticing that the Domain attribute is not for itself and ignore it. -8.3 Unexpected Cookie Sharing +7.3 Unexpected Cookie Sharing - A user agent should make every attempt to prevent the sharing of + A user agent SHOULD make every attempt to prevent the sharing of session information between hosts that are in different domains. Embedded or inlined objects may cause particularly severe privacy problems if they can be used to share cookies between disparate hosts. For example, a malicious server could embed cookie information for host a.com in a URI for a CGI on host b.com. User agent implementors are strongly encouraged to prevent this sort of exchange whenever possible. +7.4 Cookies For Account Information + While it is common practice to use them this way, cookies are not + designed or intended to be used to hold authentication information, + such as account names and passwords. Unless such cookies are + exchanged over an encrypted path, the account information they + contain is highly vulnerable to perusal and theft. -9. OTHER, SIMILAR, PROPOSALS +8. OTHER, SIMILAR, PROPOSALS - Three other proposals have been made to accomplish similar goals. - This specification is an amalgam of Kristol's State-Info proposal and - Netscape's Cookie proposal. + Apart from RFC 2109, three other proposals have been made to + accomplish similar goals. This specification began as an amalgam of + Kristol's State-Info proposal [DMK95] and Netscape's Cookie proposal + [Netscape]. > Brian Behlendorf proposed a Session-ID header that would be user-agent-initiated and could be used by an origin server to track "clicktrails". It would not carry any origin-server-defined state, however. Phillip Hallam-Baker has proposed another client-defined session ID mechanism for similar purposes. While both session IDs and cookies can provide a way to sustain stateful sessions, their intended purpose is different, and, consequently, the privacy requirements for them are different. A user initiates session IDs to allow servers to track progress through them, or to distinguish multiple users on a shared machine. Cookies are server-initiated, so the cookie mechanism described here gives users control over something that would otherwise take place without the users' awareness. Furthermore, cookies convey rich, server- selected information, whereas session IDs comprise user-selected, simple information. -10. HISTORICAL +9. HISTORICAL -10.1 Compatibility With Netscape's Implementation +9.1 Compatibility with Existing Implementations - HTTP/1.0 clients and servers may use Set-Cookie and Cookie headers - that reflect Netscape's original cookie proposal. These notes cover - inter-operation between "old" and "new" cookies. -10.1.1 Extended Cookie Header - This proposal adds attribute-value pairs to the Cookie request header - in a compatible way. An "old" client that receives a "new" cookie - will ignore attributes it does not understand; it returns what it - does understand to the origin server. A "new" client always sends - cookies in the new form. - An "old" server that receives a "new" cookie will see what it thinks - are many cookies with names that begin with a $, and it will ignore - them. (The "old" server expects these cookies to be separated by - semi-colon, not comma.) A "new" server can detect cookies that have - passed through an "old" client, because they lack a $Version - attribute. -10.1.2 Expires and Max-Age - Netscape's original proposal defined an Expires header that took a - date value in a fixed-length variant format in place of Max-Age: - Wdy, DD-Mon-YY HH:MM:SS GMT - Note that the Expires date format contains embedded spaces, and that - "old" cookies did not have quotes around values. Clients that - implement to this specification should be aware of "old" cookies and - Expires. -10.1.3 Punctuation - In Netscape's original proposal, the values in attribute-value pairs - did not accept "-quoted strings. Origin servers should be cautious - about sending values that require quotes unless they know the - receiving user agent understands them (i.e., "new" cookies). A - ("new") user agent should only use quotes around values in Cookie - headers when the cookie's version(s) is (are) all compliant with this - specification or later. - In Netscape's original proposal, no whitespace was permitted around - the = that separates attribute-value pairs. Therefore such - whitespace should be used with caution in new implementations. + Existing cookie implementations, based on the Netscape specification, + use the Set-Cookie (not Set-Cookie2) header. User agents that + receive in the same response both a Set-Cookie and Set-Cookie2 + response header for the same cookie MUST discard the Set-Cookie + information and use only the Set-Cookie2 information. Furthermore, a + user agent MUST assume, if it received a Set-Cookie2 response header, + that the sending server complies with this document and will + understand Cookie request headers that also follow this + specification. + New cookies MUST replace both equivalent old- and new-style cookies. + That is, if a user agent that follows both this specification and + Netscape's original specification receives a Set-Cookie2 response + header, and the NAME and the Domain and Path attributes match (per + the Cookie Management section) a Netscape-style cookie, the + Netscape-style cookie MUST be discarded, and the user agent MUST + retain only the cookie adhering to this specification. + Older user agents that do not understand this specification, but that + do understand Netscape's original specification, will not recognize + the Set-Cookie2 response header and will receive and send cookies + according to the older specification. + A user agent that supports both this specification and Netscape-style + cookies SHOULD send a Cookie request header that follows the older + Netscape specification if it received the cookie in a Set-Cookie + response header and not in a Set-Cookie2 response header. However, + it SHOULD send the following request header as well: + Cookie2: $Version="1" + The Cookie2 header advises the server that the user agent understands + new-style cookies. If the server understands new-style cookies, as + well, it SHOULD continue the stateful session by sending a Set- + Cookie2 response header, rather than Set-Cookie. A server that does + not understand new-style cookies will simply ignore the Cookie2 + request header.
Some caches, such as those conforming to HTTP/1.0, will inevitably cache the
Set-Cookie header, because there was no mechanism to suppress caching of headers prior to HTTP/1.1. This caching can lead to security problems. Documents transmitted by an origin server along with Set-Cookie headers will usually eitherbe uncachable, or will be "pre-expired". As long as caches obey instructions not to cache documents (following Expires: <a date in the past> or Pragma: no-cache (HTTP/1.0), or Cache-control: no-cache (HTTP/1.1)) uncachable documents present no problem. However, pre-expired documents may be stored in caches. They require validation (a conditional GET) on each new request, but some cache operators loosen the rules for their caches, and sometimes serve expired documents without first validating them. This combination of factors can lead to cookies meant for one user later The Set-Cookie header isstored in the cache, and, although the document is stale (expired), the cache returns the document in response to later requests, including cached headers.
This document really represents the collective efforts of the following people, in addition to the authors: Roy Fielding, Marc Hedlund, Ted Hardie, Koen Holtman, Shel Kaphan, Rohit Khare.
David M. Kristol Bell Laboratories, Lucent Technologies - 600 Mountain Ave. Room 2A-227 + 600 Mountain Ave. Room 2A-333 Murray Hill, NJ 07974 Phone: (908) 582-2250 - Fax: (908) 582-5809 + Fax: (908) 582-1239 EMail: firstname.lastname@example.org Lou Montulli - Netscape Communications Corp. - 501 E. Middlefield Rd. - Mountain View, CA 94043 + Epinions.com, Inc. + 2037 Landings Dr. + Mountain View, CA 94301 - Phone: (415) 528-2600 - EMail: email@example.com + EMail: firstname.lastname@example.org
+12. REFERENCES + + [DMK95] Kristol, D.M., "Proposed HTTP State-Info Mechanism", + available at <http://portal.research.bell-> + labs.com/~dmk/state-info.html>, September, 1995. + + [Netscape] "Persistent Client State -- HTTP Cookies", available at + <http://www.netscape.com/newsref/std/cookie_spec.html>, + undated. + + [RFC2109] Kristol, D. and L. Montulli, "HTTP State Management + Mechanism", RFC 2109, February 1997. + + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate + Requirement Levels", BCP 14, RFC 2119, March 1997. + + [RFC2279] Yergeau, F., "UTF-8, a transformation format of Unicode + and ISO-10646", RFC 2279, January 1998. + + [RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform + Resource Identifiers (URI): Generic Syntax", RFC 2396, + August 1998. + [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T. + Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", + RFC 2616, June 1999. +13. Full Copyright Statement + Copyright (C) The Internet Society (2000). All Rights Reserved. + This document and translations of it may be copied and furnished to + others, and derivative works that comment on or otherwise explain it + or assist in its implementation may be prepared, copied, published + and distributed, in whole or in part, without restriction of any + kind, provided that the above copyright notice and this paragraph are + included on all such copies and derivative works. However, this + document itself may not be modified in any way, such as by removing + the copyright notice or references to the Internet Society or other + Internet organizations, except as needed for the purpose of + developing Internet standards in which case the procedures for + copyrights defined in the Internet Standards process must be + followed, or as required to translate it into languages other than + English. + The limited permissions granted above are perpetual and will not be + revoked by the Internet Society or its successors or assigns. + This document and the information contained herein is provided on an + "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING + TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING + BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION + HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF + MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. +Acknowledgement + Funding for the RFC Editor function is currently provided by the + Internet Society.