This document defines the concept of an "origin", which represents a web principal. Typically, user agents isolate content retrieved from different origins to prevent a malicious web site operator from interfering with the operation of benign web sites. In particular, this document defines how to compute an origin from a URI, how to serialize an origin to a string, and an HTTP header, named "Origin", for indicating which origin caused the user agent to issue a particular HTTP request.
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2.1. Conformance Criteria
2.2. Syntax Notation
4. Comparing Origins
5. Serializing Origins
5.1. Unicode Serialization of an Origin
5.2. ASCII Serialization of an Origin
6. The HTTP Origin header
6.3. User Agent Requirements
7. Privacy Considerations
8. Security Considerations
9. IANA Considerations
10. Implementation Considerations
10.1. IDNA dependency and migration
11. Normative References
Appendix A. Acknowledgements
§ Author's Address
User agents interact with content created by a large number of authors. Although many of those authors are well-meaning, some authors might be malicious. To the extent that user agents undertake actions based on content they process, user agent implementors might wish to restrict the ability of malicious authors to disrupt the confidentiality or integrity of other content or servers.
As an example, consider an HTTP user agent that renders HTML content retrieved from various servers. If the user agent executes scripts contained in those documents, the user agent implementor might wish to prevent scripts retrieved from a malicious server from reading documents stored on an honest server, which might, for example, be behind a firewall.
Traditionally, user agents have divided content according to its "origin". More specifically, user agents allow content retrieved from one origin to interact freely with other content retrieved from that origin, but user agents restrict how that content can interact with content from another origin.
This document does not describe the restrictions user agents ought to impose on cross-origin interaction. Instead, this document defines the origin concept itself in such a way that other specifications, such for HTTP [cite] or for HTML [cite], can refer to this document for a precise, common definition of the web origin concept.
Specifically, a user agent can compute the origin of a piece of content based on the URI from which the user agent retrieved the content. Given two origins computed in this way, the user agent can compare the origins to determine if they are "the same", which is useful for performing some security checks. Finally, given an origin, the user agent can serialize that origin into either an ASCII or a Unicode representation.
This document also defines one use of the ASCII serialization: the HTTP Origin header. An Origin header attached to an HTTP request contains the ASCII serializations of the origins that caused the user agent to issue the HTTP request. The Origin header has a number of uses, including for cross-origin resource sharing [cite].
The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).
Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("MUST", "SHOULD", "MAY", etc) used in introducing the algorithm.
Conformance requirements phrased as algorithms or specific steps can be implemented in any manner, so long as the end result is equivalent. In particular, the algorithms defined in this specification are intended to be easy to understand and are not intended to be performant.
This specification uses the Augmented Backus-Naur Form (ABNF) notation of [RFC5234] (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” January 2008.).
The following core rules are included by reference, as defined in [RFC5234] (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” January 2008.), Appendix B.1: ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), HTAB (horizontal tab), CHAR (any US-ASCII character), VCHAR (any visible US-ASCII character), and WSP (whitespace).
The OWS (optional whitespace) rule is used where zero or more linear whitespace characters MAY appear:
OWS = *( [ obs-fold ] WSP ) ; "optional" whitespace obs-fold = CRLF
OWS SHOULD either not be produced or be produced as a single SP character.
The terms user agent, client, server, proxy, and origin server have the same meaning as in the HTTP/1.1 specification ([RFC2616] (Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” June 1999.), Section 1.3).
A globally unique identifier is a value which is different from all other previously existing values. For example, a sufficiently long random string is likely to be a globally unique identifier.
A idna-canonicalization host name is the string generated by the following algorithm:
An origin represents a web principal. Typically, user agents determine the origin of a piece of content from the URI from which they retrieved the content. In this section, we define how to compute an origin from a URI.
The origin of a URI is the value computed by the following algorithm:
Implementations MAY define other types of origins in addition to the scheme/host/port triple type defined above. For example, an implementation might define an origin based on a public key or an implementation might append addition "sandbox" bits to a scheme/host/port triple.
To origins are "the same" if, and only if, they are identical. In particular:
Two URIs are the same-origin if their origins are the same.
NOTE: A URI is not necessarily same-origin with itself. For example, a data URI is not same-origin with itself because data URIs do not use a server-based naming authority and therefore have globally unique identifiers as origins.
This section defines how to serialize an origin to a unicode string and to an ASCII string.
The unicode-serialization of an origin is the value returned by the following algorithm:
(i.e., the code point sequence U+006E, U+0075, U+006C, U+006C) and abort these steps.
[TODO: Check that we handle IPv6 literals correctly.]
The ascii-serialization of an origin is the value returned by the following algorithm:
(i.e., the code point sequence U+006E, U+0075, U+006C, U+006C) and abort these steps.
This section defines the HTTP Origin header.
The Origin header has the following syntax:
origin = "Origin:" OWS origin-list-or-null OWS origin-list-or-null = "null" / origin-list origin-list = serialized-origin *( SP serialized-origin ) serialized-origin = scheme "://" host [ ":" port ] ; <scheme>, <host>, <port> productions from RFC3986
When included in an HTTP request, the Origin header indicates the origin(s) that caused the user agent to issue the request.
For example, consider a user agent that executes scripts on behalf of origins. If one of those scripts causes the user agent to issue an HTTP request, the user agent might wish to use the Origin header to inform the server that the request was issued by the script.
In some cases, a number of origins contribute to causing the user agents to issue an HTTP request. In those cases, the user agent can list all the origins in the Origin header. For example, if the HTTP request was initially issued by one origin but then later redirected by another origin, the user agent might wish to inform the server that two origins were involved in causing the user agent to issue the request.
The user agent MAY include an Origin header in any HTTP request.
The user agent MUST NOT include more than one Origin header field in any HTTP request.
Whenever a user agent issues an HTTP request from a "privacy-sensitive" context, the user agent MUST send the value "null" in the Origin header.
NOTE: This document does not define the notion of a privacy-sensitive context. Applications that generate HTTP requests can designate contexts as privacy-sensitive to impose restrictions on how user agents generate Origin headers.
When generating an Origin header, the user agent MUST meet the following requirements:
If the user agent issued an HTTP request current-request because the user agent received 3xx Status Code response to another HTTP request previous-request for URI previous-uri:
The user agent SHOULD include the Origin header in an HTTP request if the user agent issues the HTTP request on behalf of an origin (e.g., not by the user operating a trusted user interface surface). In this case, the user agent SHOULD set the value of the Origin header to the ascii-serialization of that origin.
NOTE: This behavior differs from the usual user agent behavior for the HTTP Referer header, which user agents often suppress when an origin with an "https" scheme issues a request for a URI with an "http" scheme.
[TODO: Privacy considerations.]
[TODO: Security considerations.]
[TODO: Register the Origin header.]
IDNA2008 [RFC5890] (Klensin, J., “Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework,” August 2010.) supersedes IDNA2003 [RFC3490] (Faltstrom, P., Hoffman, P., and A. Costello, “Internationalizing Domain Names in Applications (IDNA),” March 2003.) but is not backwards-compatible. For this reason, there will be a transition period (possibly of a number of years). User agents SHOULD implement IDNA2008 [RFC5890] (Klensin, J., “Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework,” August 2010.) and MAY implement [Unicode Technical Standard #46 <http://unicode.org/reports/tr46/>] in order to facilitate a smoother IDNA transition. If a user agent does not implement IDNA2008, the user agent MUST implement IDNA2003 [RFC3490] (Faltstrom, P., Hoffman, P., and A. Costello, “Internationalizing Domain Names in Applications (IDNA),” March 2003.).
|[RFC2119]||Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).|
|[RFC2616]||Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P., and T. Berners-Lee, “Hypertext Transfer Protocol -- HTTP/1.1,” RFC 2616, June 1999.|
|[RFC3490]||Faltstrom, P., Hoffman, P., and A. Costello, “Internationalizing Domain Names in Applications (IDNA),” RFC 3490, March 2003 (TXT).|
See Section 10.1 (IDNA dependency and migration) for an explanation why the normative reference to an obsoleted specification is needed.
|[RFC5234]||Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” STD 68, RFC 5234, January 2008.|
|[RFC5246]||Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.2,” RFC 5246, August 2008.|
|[RFC5890]||Klensin, J., “Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework,” RFC 5890, August 2010 (TXT).|
|[RFC5891]||Klensin, J., “Internationalized Domain Names in Applications (IDNA): Protocol,” RFC 5891, August 2010 (TXT).|