draft-ietf-httpbis-origin-frame-06.txt		rfc8336.txt
	HTTP M. Nottingham		Internet Engineering Task Force (IETF) M. Nottingham
	Internet-Draft		Request for Comments: 8336
	Intended status: Standards Track E. Nygren		Category: Standards Track E. Nygren
	Expires: July 17, 2018 Akamai		ISSN: 2070-1721 Akamai Technologies
	January 13, 2018		March 2018
	The ORIGIN HTTP/2 Frame		The ORIGIN HTTP/2 Frame
	draft-ietf-httpbis-origin-frame-06
	Abstract		Abstract
	This document specifies the ORIGIN frame for HTTP/2, to indicate what		This document specifies the ORIGIN frame for HTTP/2, to indicate what
	origins are available on a given connection.		origins are available on a given connection.
	Note to Readers
	Discussion of this draft takes place on the HTTP working group
	mailing list (ietf-http-wg@w3.org), which is archived at
	https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].
	Working Group information can be found at http://httpwg.github.io/
	[2]; source code and issues list for this draft can be found at
	https://github.com/httpwg/http-extensions/labels/origin-frame [3].
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This is an Internet Standards Track document.
	provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		This document is a product of the Internet Engineering Task Force
	and may be updated, replaced, or obsoleted by other documents at any		(IETF). It represents the consensus of the IETF community. It has
	time. It is inappropriate to use Internet-Drafts as reference		received public review and has been approved for publication by the
	material or to cite them other than as "work in progress."		Internet Engineering Steering Group (IESG). Further information on
			Internet Standards is available in Section 2 of RFC 7841.
	This Internet-Draft will expire on July 17, 2018.		Information about the current status of this document, any errata,
			and how to provide feedback on it may be obtained at
			https://www.rfc-editor.org/info/rfc8336.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3		1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
	2. The ORIGIN HTTP/2 Frame . . . . . . . . . . . . . . . . . . . 3		2. The ORIGIN HTTP/2 Frame . . . . . . . . . . . . . . . . . . . 3
	2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 3		2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2.2. Processing ORIGIN Frames . . . . . . . . . . . . . . . . 4		2.2. Processing ORIGIN Frames . . . . . . . . . . . . . . . . 3
	2.3. The Origin Set . . . . . . . . . . . . . . . . . . . . . 5		2.3. The Origin Set . . . . . . . . . . . . . . . . . . . . . 4
	2.4. Authority, Push and Coalescing with ORIGIN . . . . . . . 6		2.4. Authority, Push, and Coalescing with ORIGIN . . . . . . . 6
	3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	4. Security Considerations . . . . . . . . . . . . . . . . . . . 7		4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	5. References . . . . . . . . . . . . . . . . . . . . . . . . . 7		5. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
	5.1. Normative References . . . . . . . . . . . . . . . . . . 7		5.1. Normative References . . . . . . . . . . . . . . . . . . 8
	5.2. Informative References . . . . . . . . . . . . . . . . . 8		5.2. Informative References . . . . . . . . . . . . . . . . . 8
	5.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 9		Appendix A. Non-Normative Processing Algorithm . . . . . . . . . 10
	Appendix A. Non-Normative Processing Algorithm . . . . . . . . . 9		Appendix B. Operational Considerations for Servers . . . . . . . 10
	Appendix B. Operational Considerations for Servers . . . . . . . 9		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
	1. Introduction		1. Introduction
	HTTP/2 [RFC7540] allows clients to coalesce different origins		HTTP/2 [RFC7540] allows clients to coalesce different origins
	[RFC6454] onto the same connection when certain conditions are met.		[RFC6454] onto the same connection when certain conditions are met.
	However, in certain cases, a connection is not usable for a coalesced		However, in some cases, a connection is not usable for a coalesced
	origin, so the 421 (Misdirected Request) status code ([RFC7540],		origin, so the 421 (Misdirected Request) status code ([RFC7540],
	Section 9.1.2) was defined.		Section 9.1.2) was defined.
	Using a status code in this manner allows clients to recover from		Using a status code in this manner allows clients to recover from
	misdirected requests, but at the penalty of adding latency. To		misdirected requests, but at the penalty of adding latency. To
	address that, this specification defines a new HTTP/2 frame type,		address that, this specification defines a new HTTP/2 frame type,
	"ORIGIN", to allow servers to indicate what origins a connection is		"ORIGIN", to allow servers to indicate for which origins a connection
	usable for.		is usable.
	Additionally, experience has shown that HTTP/2's requirement to		Additionally, experience has shown that HTTP/2's requirement to
	establish server authority using both DNS and the server's		establish server authority using both DNS and the server's
	certificate is onerous. This specification relaxes the requirement		certificate is onerous. This specification relaxes the requirement
	to check DNS when the ORIGIN frame is in use. Doing so has		to check DNS when the ORIGIN frame is in use. Doing so has
	additional benefits, such as removing the latency associated with		additional benefits, such as removing the latency associated with
	some DNS lookups.		some DNS lookups.
	1.1. Notational Conventions		1.1. Notational Conventions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	2. The ORIGIN HTTP/2 Frame		2. The ORIGIN HTTP/2 Frame
	This document defines a new HTTP/2 frame type ([RFC7540], Section 4)		This document defines a new HTTP/2 frame type ([RFC7540], Section 4)
	called ORIGIN, that allows a server to indicate what origin(s)		called ORIGIN, that allows a server to indicate what origin(s)
	[RFC6454] the server would like the client to consider as members of		[RFC6454] the server would like the client to consider as members of
	the Origin Set (Section 2.3) for the connection it occurs within.		the Origin Set (Section 2.3) for the connection within which it
			occurs.
	2.1. Syntax		2.1. Syntax
	The ORIGIN frame type is 0xc (decimal 12), and contains zero or more		The ORIGIN frame type is 0xc (decimal 12) and contains zero or more
	instances of the Origin-Entry field.		instances of the Origin-Entry field.
	+-------------------------------+-------------------------------+		+-------------------------------+-------------------------------+
	| Origin-Entry (*) ...		| Origin-Entry (*) ...
	+-------------------------------+-------------------------------+		+-------------------------------+-------------------------------+
	An Origin-Entry is a length-delimited string:		An Origin-Entry is a length-delimited string:
	+-------------------------------+-------------------------------+		+-------------------------------+-------------------------------+
	| Origin-Len (16) | ASCII-Origin? ...		| Origin-Len (16) | ASCII-Origin? ...
	skipping to change at page 4, line 10 ¶		skipping to change at page 3, line 45 ¶
	sender asserts this connection is or could be authoritative for.		sender asserts this connection is or could be authoritative for.
	The ORIGIN frame does not define any flags. However, future updates		The ORIGIN frame does not define any flags. However, future updates
	to this specification MAY define flags. See Section 2.2.		to this specification MAY define flags. See Section 2.2.
	2.2. Processing ORIGIN Frames		2.2. Processing ORIGIN Frames
	The ORIGIN frame is a non-critical extension to HTTP/2. Endpoints		The ORIGIN frame is a non-critical extension to HTTP/2. Endpoints
	that do not support this frame can safely ignore it upon receipt.		that do not support this frame can safely ignore it upon receipt.
	When received by an implementing client, it is used to initialise and		When received by an implementing client, it is used to initialize and
	manipulate the Origin Set (see Section 2.3), thereby changing how the		manipulate the Origin Set (see Section 2.3), thereby changing how the
	client establishes authority for origin servers (see Section 2.4).		client establishes authority for origin servers (see Section 2.4).
	The ORIGIN frame MUST be sent on stream 0; an ORIGIN frame on any		The ORIGIN frame MUST be sent on stream 0; an ORIGIN frame on any
	other stream is invalid and MUST be ignored.		other stream is invalid and MUST be ignored.
	Likewise, the ORIGIN frame is only valid on connections with the "h2"		Likewise, the ORIGIN frame is only valid on connections with the "h2"
	protocol identifier, or when specifically nominated by the protocol's		protocol identifier or when specifically nominated by the protocol's
	definition; it MUST be ignored when received on a connection with the		definition; it MUST be ignored when received on a connection with the
	"h2c" protocol identifier.		"h2c" protocol identifier.
	This specification does not define any flags for the ORIGIN frame,		This specification does not define any flags for the ORIGIN frame,
	but future updates to this specification (through IETF consensus)		but future updates to this specification (through IETF consensus)
	might use them to change its semantics. The first four flags (0x1,		might use them to change its semantics. The first four flags (0x1,
	0x2, 0x4 and 0x8) are reserved for backwards-incompatible changes,		0x2, 0x4, and 0x8) are reserved for backwards-incompatible changes;
	and therefore when any of them are set, the ORIGIN frame containing		therefore, when any of them are set, the ORIGIN frame containing them
	them MUST be ignored by clients conforming to this specification,		MUST be ignored by clients conforming to this specification, unless
	unless the flag's semantics are understood. The remaining flags are		the flag's semantics are understood. The remaining flags are
	reserved for backwards-compatible changes, and do not affect		reserved for backwards-compatible changes and do not affect
	processing by clients conformant to this specification.		processing by clients conformant to this specification.
	The ORIGIN frame describes a property of the connection, and		The ORIGIN frame describes a property of the connection and therefore
	therefore is processed hop-by-hop. An intermediary MUST NOT forward		is processed hop by hop. An intermediary MUST NOT forward ORIGIN
	ORIGIN frames. Clients configured to use a proxy MUST ignore any		frames. Clients configured to use a proxy MUST ignore any ORIGIN
	ORIGIN frames received from it.		frames received from it.
	Each ASCII-Origin field in the frame's payload MUST be parsed as an		Each ASCII-Origin field in the frame's payload MUST be parsed as an
	ASCII serialisation of an origin ([RFC6454], Section 6.2). If		ASCII serialization of an origin ([RFC6454], Section 6.2). If
	parsing fails, the field MUST be ignored.		parsing fails, the field MUST be ignored.
	Note that the ORIGIN frame does not support wildcard names (e.g.,		Note that the ORIGIN frame does not support wildcard names (e.g.,
	"*.example.com") in Origin-Entry. As a result, sending ORIGIN when a		"*.example.com") in Origin-Entry. As a result, sending ORIGIN when a
	wildcard certificate is in use effectively disables any origins that		wildcard certificate is in use effectively disables any origins that
	are not explicitly listed in the ORIGIN frame(s) (when the client		are not explicitly listed in the ORIGIN frame(s) (when the client
	understands ORIGIN).		understands ORIGIN).
	See Appendix A for an illustrative algorithm for processing ORIGIN		See Appendix A for an illustrative algorithm for processing ORIGIN
	frames.		frames.
	2.3. The Origin Set		2.3. The Origin Set
	The set of origins (as per [RFC6454]) that a given connection might		The set of origins (as per [RFC6454]) that a given connection might
	be used for is known in this specification as the Origin Set.		be used for is known in this specification as the Origin Set.
	By default, the Origin Set for a connection is uninitialised. An		By default, the Origin Set for a connection is uninitialized. An
	uninitialized Origin Set means that clients apply the coalescing		uninitialized Origin Set means that clients apply the coalescing
	rules from Section 9.1.1 of [RFC7540].		rules from Section 9.1.1 of [RFC7540].
	When an ORIGIN frame is first received and successfully processed by		When an ORIGIN frame is first received and successfully processed by
	a client, the connection's Origin Set is defined to contain an		a client, the connection's Origin Set is defined to contain an
	initial origin. The initial origin is composed from:		initial origin. The initial origin is composed from:
	o Scheme: "https"		o Scheme: "https"
	o Host: the value sent in Server Name Indication (SNI, [RFC6066],		o Host: the value sent in Server Name Indication (SNI) ([RFC6066],
	Section 3), converted to lower case; if SNI is not present, the		Section 3) converted to lower case; if SNI is not present, the
	remote address of the connection (i.e., the server's IP address)		remote address of the connection (i.e., the server's IP address)
	o Port: the remote port of the connection (i.e., the server's port)		o Port: the remote port of the connection (i.e., the server's port)
	The contents of that ORIGIN frame (and subsequent ones) allows the		The contents of that ORIGIN frame (and subsequent ones) allow the
	server to incrementally add new origins to the Origin Set, as		server to incrementally add new origins to the Origin Set, as
	described in Section 2.2.		described in Section 2.2.
	The Origin Set is also affected by the 421 (Misdirected Request)		The Origin Set is also affected by the 421 (Misdirected Request)
	response status code, defined in [RFC7540], Section 9.1.2. Upon		response status code, as defined in [RFC7540], Section 9.1.2. Upon
	receipt of a response with this status code, implementing clients		receipt of a response with this status code, implementing clients
	MUST create the ASCII serialisation of the corresponding request's		MUST create the ASCII serialization of the corresponding request's
	origin (as per [RFC6454], Section 6.2) and remove it from the		origin (as per [RFC6454], Section 6.2) and remove it from the
	connection's Origin Set, if present.		connection's Origin Set, if present.
	Note: When sending an ORIGIN frame to a connection that is		Note: When sending an ORIGIN frame to a connection that is
	initialised as an Alternative Service [RFC7838], the initial		initialized as an alternative service [RFC7838], the initial
	origin set (Section 2.3) will contain an origin with the		Origin Set (Section 2.3) will contain an origin with the
	appropriate scheme and hostname (since Alternative Services		appropriate scheme and hostname (since RFC 7838 specifies that the
	specifies that the origin's hostname be sent in SNI). However, it		origin's hostname be sent in SNI). However, it is possible that
	is possible that the port will be different than that of the		the port will be different than that of the intended origin, since
	intended origin, since the initial origin set is calculated using		the initial Origin Set is calculated using the actual port in use,
	the actual port in use, which can be different for the alternative		which can be different for the alternative service. In this case,
	service. In this case, the intended origin needs to be sent in		the intended origin needs to be sent in the ORIGIN frame
	the ORIGIN frame explicitly.		explicitly.
	For example, a client making requests for "https://example.com" is		For example, a client making requests for "https://example.com" is
	directed to an alternative service at ("h2", "x.example.net",		directed to an alternative service at ("h2", "x.example.net",
	"8443"). If this alternative service sends an ORIGIN frame, the		"8443"). If this alternative service sends an ORIGIN frame, the
	initial origin will be "https://example.com:8443". The client		initial origin will be "https://example.com:8443". The client
	will not be able to use the alternative service to make requests		will not be able to use the alternative service to make requests
	for "https://example.com" unless that origin is explicitly		for "https://example.com" unless that origin is explicitly
	included in the ORIGIN frame.		included in the ORIGIN frame.
	2.4. Authority, Push and Coalescing with ORIGIN		2.4. Authority, Push, and Coalescing with ORIGIN
	Section 10.1 of [RFC7540] uses both DNS and the presented TLS		Section 10.1 of [RFC7540] uses both DNS and the presented Transport
	certificate to establish the origin server(s) that a connection is		Layer Security (TLS) certificate to establish the origin server(s)
	authoritative for, just as HTTP/1.1 does in [RFC7230].		that a connection is authoritative for, just as HTTP/1.1 does in
			[RFC7230].
	Furthermore, Section 9.1.1 of [RFC7540] explicitly allows a		Furthermore, Section 9.1.1 of [RFC7540] explicitly allows a
	connection to be used for more than one origin server, if it is		connection to be used for more than one origin server, if it is
	authoritative. This affects what responses can be considered		authoritative. This affects what responses can be considered
	authoritative, both for direct responses to requests and for server		authoritative, both for direct responses to requests and for server
	push (see [RFC7540], Section 8.2.2). Indirectly, it also affects		push (see [RFC7540], Section 8.2.2). Indirectly, it also affects
	what requests will be sent on a connection, since clients will		what requests will be sent on a connection, since clients will
	generally only send requests on connections that they believe to be		generally only send requests on connections that they believe to be
	authoritative for the origin in question.		authoritative for the origin in question.
	Once an Origin Set has been initialised for a connection, clients		Once an Origin Set has been initialized for a connection, clients
	that implement this specification use it to help determine what the		that implement this specification use it to help determine what the
	connection is authoritative for. Specifically, such clients MUST NOT		connection is authoritative for. Specifically, such clients MUST NOT
	consider a connection to be authoritative for an origin not present		consider a connection to be authoritative for an origin not present
	in the Origin Set, and SHOULD use the connection for all requests to		in the Origin Set, and they SHOULD use the connection for all
	origins in the Origin Set for which the connection is authoritative,		requests to origins in the Origin Set for which the connection is
	unless there are operational reasons for opening a new connection.		authoritative, unless there are operational reasons for opening a new
			connection.
	Note that for a connection to be considered authoritative for a given		Note that for a connection to be considered authoritative for a given
	origin, the server is still required to authenticate with certificate		origin, the server is still required to authenticate with a
	that passes suitable checks; see Section 9.1.1 of [RFC7540] for more		certificate that passes suitable checks; see Section 9.1.1 of
	information. This includes verifying that the host matches a		[RFC7540] for more information. This includes verifying that the
	"dNSName" value from the certificate "subjectAltName" field (using		host matches a "dNSName" value from the certificate "subjectAltName"
	the rules defined in [RFC2818]; see also [RFC5280], Section 4.2.1.6).		field (using the rules defined in [RFC2818]; see also [RFC5280],
			Section 4.2.1.6).
	Additionally, clients MAY avoid consulting DNS to establish the		Additionally, clients MAY avoid consulting DNS to establish the
	connection's authority for new requests to origins in the Origin Set;		connection's authority for new requests to origins in the Origin Set;
	however, those that do so face new risks, as explained in Section 4.		however, those that do so face new risks, as explained in Section 4.
	Because ORIGIN can change the set of origins a connection is used for		Because ORIGIN can change the set of origins a connection is used for
	over time, it is possible that a client might have more than one		over time, it is possible that a client might have more than one
	viable connection to an origin open at any time. When this occurs,		viable connection to an origin open at any time. When this occurs,
	clients SHOULD NOT emit new requests on any connection whose Origin		clients SHOULD NOT emit new requests on any connection whose Origin
	Set is a proper subset of another connection's Origin Set, and SHOULD		Set is a proper subset of another connection's Origin Set, and they
	close it once all outstanding requests are satisfied.		SHOULD close it once all outstanding requests are satisfied.
	The Origin Set is unaffected by any alternative services [RFC7838]		The Origin Set is unaffected by any alternative services [RFC7838]
	advertisements made by the server. Advertising an alternative		advertisements made by the server. Advertising an alternative
	service does not affect whether a server is authoritative.		service does not affect whether a server is authoritative.
	3. IANA Considerations		3. IANA Considerations
	This specification adds an entry to the "HTTP/2 Frame Type" registry.		This specification adds an entry to the "HTTP/2 Frame Type" registry.
	o Frame Type: ORIGIN		o Frame Type: ORIGIN
	o Code: 0xc		o Code: 0xc
	o Specification: [this document]		o Specification: RFC 8336
	4. Security Considerations		4. Security Considerations
	Clients that blindly trust the ORIGIN frame's contents will be		Clients that blindly trust the ORIGIN frame's contents will be
	vulnerable to a large number of attacks. See Section 2.4 for		vulnerable to a large number of attacks. See Section 2.4 for
	mitigations.		mitigations.
	Relaxing the requirement to consult DNS when determining authority		Relaxing the requirement to consult DNS when determining authority
	for an origin means that an attacker who possesses a valid		for an origin means that an attacker who possesses a valid
	certificate no longer needs to be on-path to redirect traffic to		certificate no longer needs to be on path to redirect traffic to
	them; instead of modifying DNS, they need only convince the user to		them; instead of modifying DNS, they need only convince the user to
	visit another Web site in order to coalesce connections to the target		visit another website in order to coalesce connections to the target
	onto their existing connection.		onto their existing connection.
	As a result, clients opting not to consult DNS ought to employ some		As a result, clients opting not to consult DNS ought to employ some
	alternative means to establish a high degree of confidence that the		alternative means to establish a high degree of confidence that the
	certificate is legitimate. For example, clients might skip		certificate is legitimate. For example, clients might skip
	consulting DNS only if they receive proof of inclusion in a		consulting DNS only if they receive proof of inclusion in a
	Certificate Transparency log [RFC6962] or they have a recent OCSP		Certificate Transparency log [RFC6962] or if they have a recent
	response [RFC6960] (possibly using the "status_request" TLS extension		Online Certificate Status Protocol (OCSP) response [RFC6960]
	[RFC6066]) showing that the certificate was not revoked.		(possibly using the "status_request" TLS extension [RFC6066]) showing
			that the certificate was not revoked.
	The Origin Set's size is unbounded by this specification, and thus		The Origin Set's size is unbounded by this specification and thus
	could be used by attackers to exhaust client resources. To mitigate		could be used by attackers to exhaust client resources. To mitigate
	this risk, clients can monitor their state commitment and close the		this risk, clients can monitor their state commitment and close the
	connection if it is too high.		connection if it is too high.
	5. References		5. References
	5.1. Normative References		5.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	skipping to change at page 9, line 5 ¶		skipping to change at page 10, line 5 ¶
	<https://www.rfc-editor.org/info/rfc7230>.		<https://www.rfc-editor.org/info/rfc7230>.
	[RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP		[RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP
	Alternative Services", RFC 7838, DOI 10.17487/RFC7838,		Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
	April 2016, <https://www.rfc-editor.org/info/rfc7838>.		April 2016, <https://www.rfc-editor.org/info/rfc7838>.
	[RFC8288] Nottingham, M., "Web Linking", RFC 8288,		[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
	DOI 10.17487/RFC8288, October 2017,		DOI 10.17487/RFC8288, October 2017,
	<https://www.rfc-editor.org/info/rfc8288>.		<https://www.rfc-editor.org/info/rfc8288>.
	5.3. URIs
	[1] https://lists.w3.org/Archives/Public/ietf-http-wg/
	[2] http://httpwg.github.io/
	[3] https://github.com/httpwg/http-extensions/labels/origin-frame
	Appendix A. Non-Normative Processing Algorithm		Appendix A. Non-Normative Processing Algorithm
	The following algorithm illustrates how a client could handle		The following algorithm illustrates how a client could handle
	received ORIGIN frames:		received ORIGIN frames:
	1. If the client is configured to use a proxy for the connection,		1. If the client is configured to use a proxy for the connection,
	ignore the frame and stop processing.		ignore the frame and stop processing.
	2. If the connection is not identified with the "h2" protocol		2. If the connection is not identified with the "h2" protocol
	identifier or another protocol that has explicitly opted into		identifier or another protocol that has explicitly opted into
	this specification, ignore the frame and stop processing.		this specification, ignore the frame and stop processing.
	3. If the frame occurs upon any stream except stream 0, ignore the		3. If the frame occurs upon any stream except stream 0, ignore the
	frame and stop processing.		frame and stop processing.
	4. If any of the flags 0x1, 0x2, 0x4 or 0x8 are set, ignore the		4. If any of the flags 0x1, 0x2, 0x4, or 0x8 are set, ignore the
	frame and stop processing.		frame and stop processing.
	5. If no previous ORIGIN frame on the connection has reached this		5. If no previous ORIGIN frame on the connection has reached this
	step, initialise the Origin Set as per Section 2.3.		step, initialize the Origin Set as per Section 2.3.
	6. For each "Origin-Entry" in the frame payload:		6. For each "Origin-Entry" in the frame payload:
	1. Parse "ASCII-Origin" as an ASCII serialization of an origin		1. Parse "ASCII-Origin" as an ASCII serialization of an origin
	([RFC6454], Section 6.2) and let the result be		([RFC6454], Section 6.2), and let the result be
	"parsed_origin". If parsing fails, skip to the next "Origin-		"parsed_origin". If parsing fails, skip to the next
	Entry".		"Origin-Entry".
	2. Add "parsed_origin" to the Origin Set.		2. Add "parsed_origin" to the Origin Set.
	Appendix B. Operational Considerations for Servers		Appendix B. Operational Considerations for Servers
	The ORIGIN frame allows a server to indicate for which origins a		The ORIGIN frame allows a server to indicate for which origins a
	given connection ought be used. The set of origins advertised using		given connection ought be used. The set of origins advertised using
	this mechanism is under control of the server; servers are not		this mechanism is under control of the server; servers are not
	obligated to use it, or to advertise all origins which they might be		obligated to use it or to advertise all origins that they might be
	able to answer a request for.		able to answer a request for.
	For example, it can be used to inform the client that the connection		For example, it can be used to inform the client that the connection
	is to only be used for the SNI-based origin, by sending an empty		is to only be used for the SNI-based origin, by sending an empty
	ORIGIN frame. Or, a larger number of origins can be indicated by		ORIGIN frame. Or, a larger number of origins can be indicated by
	including a payload.		including a payload.
	Generally, this information is most useful to send before sending any		Generally, this information is most useful to send before sending any
	part of a response that might initiate a new connection; for example,		part of a response that might initiate a new connection; for example,
	"Link" header fields [RFC8288] in a response HEADERS, or links in the		"Link" response header fields [RFC8288], or links in the response
	response body.		body.
	Therefore, the ORIGIN frame ought be sent as soon as possible on a		Therefore, the ORIGIN frame ought be sent as soon as possible on a
	connection, ideally before any HEADERS or PUSH_PROMISE frames.		connection, ideally before any HEADERS or PUSH_PROMISE frames.
	However, if it's desirable to associate a large number of origins		However, if it's desirable to associate a large number of origins
	with a connection, doing so might introduce end-user perceived		with a connection, doing so might introduce end-user-perceived
	latency, due to their size. As a result, it might be necessary to		latency, due to their size. As a result, it might be necessary to
	select a "core" set of origins to send initially, expanding the set		select a "core" set of origins to send initially, and expand the set
	of origins the connection is used for with subsequent ORIGIN frames		of origins the connection is used for with subsequent ORIGIN frames
	later (e.g., when the connection is idle).		later (e.g., when the connection is idle).
	That said, senders are encouraged to include as many origins as		That said, senders are encouraged to include as many origins as
	practical within a single ORIGIN frame; clients need to make		practical within a single ORIGIN frame; clients need to make
	decisions about creating connections on the fly, and if the origin		decisions about creating connections on the fly, and if the Origin
	set is split across many frames, their behaviour might be suboptimal.		Set is split across many frames, their behavior might be suboptimal.
	Senders take note that, as per Section 4, Step 5 of [RFC6454], the		Senders take note that, as per Section 4, Step 5, of [RFC6454], the
	values in an ORIGIN header need to be case-normalised before		values in an ORIGIN header need to be case-normalized before
	serialisation.		serialization.
	Finally, servers that host alternative services [RFC7838] will need		Finally, servers that host alternative services [RFC7838] will need
	to explicitly advertise their origins when sending ORIGIN, because		to explicitly advertise their origins when sending ORIGIN, because
	the default contents of the Origin Set (as per Section 2.3) do not		the default contents of the Origin Set (as per Section 2.3) do not
	contain any Alternative Services' origins, even if they have been		contain any alternative services' origins, even if they have been
	used previously on the connection.		used previously on the connection.
	Authors' Addresses		Authors' Addresses
	Mark Nottingham		Mark Nottingham
	Email: mnot@mnot.net		Email: mnot@mnot.net
	URI: https://www.mnot.net/		URI: https://www.mnot.net/
	Erik Nygren		Erik Nygren
	Akamai		Akamai Technologies
	Email: nygren@akamai.com		Email: erik+ietf@nygren.org
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