< draft-ietf-oauth-v2-http-mac-01.txt		draft-ietf-oauth-v2-http-mac-02.txt >
	Network Working Group E. Hammer-Lahav, Ed.		OAuth J. Richer, Ed.
	Internet-Draft February 8, 2012		Internet-Draft The MITRE Corporation
	Intended status: Standards Track		Intended status: Standards Track W. Mills, Ed.
	Expires: August 11, 2012		Expires: May 30, 2013 Yahoo! Inc.
			H. Tschofenig, Ed.
			Nokia Siemens Networks
			November 28, 2012
	HTTP Authentication: MAC Access Authentication		OAuth 2.0 Message Authentication Code (MAC) Tokens
	draft-ietf-oauth-v2-http-mac-01		draft-ietf-oauth-v2-http-mac-02
	Abstract		Abstract
	This document specifies the HTTP MAC access authentication scheme, an		This document specifies the HTTP MAC access authentication scheme, an
	HTTP authentication method using a message authentication code (MAC)		HTTP authentication method using a message authentication code (MAC)
	algorithm to provide cryptographic verification of portions of HTTP		algorithm to provide cryptographic verification of portions of HTTP
	requests. The document also defines an OAuth 2.0 binding for use as		requests. The document also defines an OAuth 2.0 binding for use as
	an access-token type.		an access token type.
			NOTE: This document (and other OAuth 2.0 security documents, such as
			[I-D.tschofenig-oauth-hotk]) are still work in progress in the OAuth
			working group. As such, the content of this document may change.
			For a discussion about security requirements please consult [I-D
			.tschofenig-oauth-security]. Your input on the detailed security
			requirements is highly appreciated.
	Status of this Memo		Status of this Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on August 11, 2012.		This Internet-Draft will expire on May 30, 2013.
	Copyright Notice		Copyright Notice
	Copyright (c) 2012 IETF Trust and the persons identified as the		Copyright (c) 2012 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
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	publication of this document. Please review these documents		Please review these documents carefully, as they describe your rights
	carefully, as they describe your rights and restrictions with respect		and restrictions with respect to this document. Code Components
	to this document. Code Components extracted from this document must		extracted from this document must include Simplified BSD License text
	include Simplified BSD License text as described in Section 4.e of		as described in Section 4.e of the Trust Legal Provisions and are
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	described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4		1.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 3
	1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 5		1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 5
	2. Issuing MAC Credentials . . . . . . . . . . . . . . . . . . . 5		2. Issuing MAC Credentials . . . . . . . . . . . . . . . . . . . 5
	3. Making Requests . . . . . . . . . . . . . . . . . . . . . . . 6		3. Making Requests . . . . . . . . . . . . . . . . . . . . . . . 6
	3.1. The "Authorization" Request Header . . . . . . . . . . . . 6		3.1. The "Authorization" Request Header . . . . . . . . . . . . 6
	3.2. Request MAC . . . . . . . . . . . . . . . . . . . . . . . 7		3.2. Request MAC . . . . . . . . . . . . . . . . . . . . . . . 7
	3.2.1. Normalized Request String . . . . . . . . . . . . . . 8		3.2.1. Normalized Request String . . . . . . . . . . . . . . 7
	3.2.2. hmac-sha-1 . . . . . . . . . . . . . . . . . . . . . . 9		3.2.2. hmac-sha-1 . . . . . . . . . . . . . . . . . . . . . . 8
	3.2.3. hmac-sha-256 . . . . . . . . . . . . . . . . . . . . . 9		3.2.3. hmac-sha-256 . . . . . . . . . . . . . . . . . . . . . 9
	4. Verifying Requests . . . . . . . . . . . . . . . . . . . . . . 10		4. Verifying Requests . . . . . . . . . . . . . . . . . . . . . . 9
	4.1. Timestamp Verification . . . . . . . . . . . . . . . . . . 10		4.1. Timestamp Verification . . . . . . . . . . . . . . . . . . 9
	4.2. The "WWW-Authenticate" Response Header Field . . . . . . . 11		4.2. The "WWW-Authenticate" Response Header Field . . . . . . . 10
	5. Use with OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . 12		5. Use with OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . 11
	5.1. Issuing MAC-Type Access Tokens . . . . . . . . . . . . . . 12		5.1. Issuing MAC-Type Access Tokens . . . . . . . . . . . . . . 11
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 13		6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	6.1. MAC Keys Transmission . . . . . . . . . . . . . . . . . . 13		6.1. MAC Keys Transmission . . . . . . . . . . . . . . . . . . 12
	6.2. Confidentiality of Requests . . . . . . . . . . . . . . . 13		6.2. Confidentiality of Requests . . . . . . . . . . . . . . . 12
	6.3. Spoofing by Counterfeit Servers . . . . . . . . . . . . . 13		6.3. Spoofing by Counterfeit Servers . . . . . . . . . . . . . 12
	6.4. Plaintext Storage of Credentials . . . . . . . . . . . . . 13		6.4. Plaintext Storage of Credentials . . . . . . . . . . . . . 12
	6.5. Entropy of MAC Keys . . . . . . . . . . . . . . . . . . . 14		6.5. Entropy of MAC Keys . . . . . . . . . . . . . . . . . . . 13
	6.6. Denial of Service / Resource Exhaustion Attacks . . . . . 14		6.6. Denial of Service / Resource Exhaustion Attacks . . . . . 13
	6.7. Timing Attacks . . . . . . . . . . . . . . . . . . . . . . 15		6.7. Timing Attacks . . . . . . . . . . . . . . . . . . . . . . 14
	6.8. CSRF Attacks . . . . . . . . . . . . . . . . . . . . . . . 15		6.8. CSRF Attacks . . . . . . . . . . . . . . . . . . . . . . . 14
	6.9. Coverage Limitations . . . . . . . . . . . . . . . . . . . 15		6.9. Coverage Limitations . . . . . . . . . . . . . . . . . . . 14
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
	7.1. The HTTP MAC Authentication Scheme Algorithm Registry . . 16		7.1. The HTTP MAC Authentication Scheme Algorithm Registry . . 15
	7.1.1. Registration Template . . . . . . . . . . . . . . . . 17		7.1.1. Registration Template . . . . . . . . . . . . . . . . 15
	7.1.2. Initial Registry Contents . . . . . . . . . . . . . . 17		7.1.2. Initial Registry Contents . . . . . . . . . . . . . . 16
	7.2. OAuth Access Token Type Registration . . . . . . . . . . . 17		7.2. OAuth Access Token Type Registration . . . . . . . . . . . 16
	7.2.1. The "mac" OAuth Access Token Type . . . . . . . . . . 17		7.2.1. The "mac" OAuth Access Token Type . . . . . . . . . . 16
	7.3. OAuth Parameters Registration . . . . . . . . . . . . . . 18		7.3. OAuth Parameters Registration . . . . . . . . . . . . . . 17
	7.3.1. The "mac_key" OAuth Parameter . . . . . . . . . . . . 18		7.3.1. The "mac_key" OAuth Parameter . . . . . . . . . . . . 17
	7.3.2. The "mac_algorithm" OAuth Parameter . . . . . . . . . 18		7.3.2. The "mac_algorithm" OAuth Parameter . . . . . . . . . 17
	8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18		8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 17
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18		9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
	9.1. Normative References . . . . . . . . . . . . . . . . . . . 18		10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
	9.2. Informative References . . . . . . . . . . . . . . . . . . 19		10.1. Normative References . . . . . . . . . . . . . . . . . . 17
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 20		10.2. Informative References . . . . . . . . . . . . . . . . . 18
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
	1. Introduction		1. Introduction
	This specification defines the HTTP MAC access authentication scheme,		This specification defines the HTTP MAC access authentication scheme,
	providing a method for making authenticated HTTP requests with		providing a method for making authenticated HTTP requests with
	partial cryptographic verification of the request, covering the HTTP		partial cryptographic verification of the request, covering the HTTP
	method, request URI, and host.		method, request URI, and host.
	Similar to the HTTP Basic access authentication scheme [RFC2617], the		Similar to the HTTP Basic access authentication scheme [RFC2617], the
	MAC scheme utilizes a set of client credentials which include an		MAC scheme utilizes a set of client credentials which include an
	identifier and key. However, in contrast with the Basic scheme, the		identifier and key. However, in contrast with the Basic scheme, the
	key is never included in authenticated requests but is used to		key is never included in authenticated requests but is used to
	calculate the request MAC value which is included instead.		calculate the request MAC value which is included instead.
	skipping to change at page 4, line 23 ¶		skipping to change at page 4, line 14 ¶
	The resource server returns the following authentication challenge:		The resource server returns the following authentication challenge:
	HTTP/1.1 401 Unauthorized		HTTP/1.1 401 Unauthorized
	WWW-Authenticate: MAC		WWW-Authenticate: MAC
	The client has previously obtained a set of MAC credentials for		The client has previously obtained a set of MAC credentials for
	accessing resources on the "http://example.com/" server. The MAC		accessing resources on the "http://example.com/" server. The MAC
	credentials issued to the client include the following attributes:		credentials issued to the client include the following attributes:
	MAC key identifier: h480djs93hd8		MAC key identifier: h480djs93hd8
	MAC key: 489dks293j39
	MAC algorithm: hmac-sha-1		MAC key: 489dks293j39
			MAC algorithm: hmac-sha-1
	The client constructs the authentication header by calculating a		The client constructs the authentication header by calculating a
	timestamp (e.g. the number of seconds since January 1, 1970 00:00:00		timestamp (e.g. the number of seconds since January 1, 1970 00:00:00
	GMT) and generating a random string used as a nonce:		GMT) and generating a random string used as a nonce:
	Timestamp: 1336363200		Timestamp: 1336363200
	Nonce: dj83hs9s
			Nonce: dj83hs9s
	The client constructs the normalized request string (the new line		The client constructs the normalized request string (the new line
	separator character is represented by "\n" for display purposes only;		separator character is represented by "\n" for display purposes only;
	the trailing new line separator signify that no extension value is		the trailing new line separator signify that no extension value is
	included with the request, explained below):		included with the request, explained below):
	1336363200\n		1336363200\n
	dj83hs9s\n		dj83hs9s\n
	GET\n		GET\n
	/resource/1?b=1&a=2\n		/resource/1?b=1&a=2\n
	skipping to change at page 5, line 39 ¶		skipping to change at page 5, line 31 ¶
	'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this		'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this
	specification are to be interpreted as described in [RFC2119].		specification are to be interpreted as described in [RFC2119].
	This specification uses the Augmented Backus-Naur Form (ABNF)		This specification uses the Augmented Backus-Naur Form (ABNF)
	notation of [I-D.ietf-httpbis-p1-messaging]. Additionally, the		notation of [I-D.ietf-httpbis-p1-messaging]. Additionally, the
	following rules are included from [RFC2617]: auth-param.		following rules are included from [RFC2617]: auth-param.
	2. Issuing MAC Credentials		2. Issuing MAC Credentials
	This specification provides one method for issuing MAC credentials		This specification provides one method for issuing MAC credentials
	using OAuth 2.0 as described in Section 5. This specification does		using OAuth 2.0 as described in Section 5. This specification does
	not mandate servers to support any particular method for issuing MAC		not mandate servers to support any particular method for issuing MAC
	credentials, and other methods MAY be defined and used. Whenever MAC		credentials, and other methods MAY be defined and used. Whenever MAC
	credentials are issued, the credentials MUST include the following		credentials are issued, the credentials MUST include the following
	attributes:		attributes:
	MAC key identifier		MAC key identifier
	A string identifying the MAC key used to calculate the request		A string identifying the MAC key used to calculate the request
	MAC. The string is usually opaque to the client. The server		MAC. The string is usually opaque to the client. The server
	typically assigns a specific scope and lifetime to each set of		typically assigns a specific scope and lifetime to each set of
	MAC credentials. The identifier MAY denote a unique value used		MAC credentials. The identifier MAY denote a unique value used
	to retrieve the authorization information (e.g. from a		to retrieve the authorization information (e.g. from a
	database), or self-contain the authorization information in a		database), or self-contain the authorization information in a
	verifiable manner (i.e. a string consisting of some data and a		verifiable manner (i.e. a string consisting of some data and a
	signature).		signature).
	MAC key		MAC key
	A shared symmetric secret used as the MAC algorithm key. The		A shared symmetric secret used as the MAC algorithm key. The
	server MUST NOT reissue a previously issued MAC key and MAC key		server MUST NOT reissue a previously issued MAC key and MAC key
	identifier combination.		identifier combination.
	MAC algorithm		MAC algorithm
	A MAC algorithm used to calculate the request MAC. Value MUST		A MAC algorithm used to calculate the request MAC. Value MUST
	be one of "hmac-sha-1", "hmac-sha-256", or a registered		be one of "hmac-sha-1", "hmac-sha-256", or a registered
	extension algorithm name as described in Section 7.1.		extension algorithm name as described in Section 7.1.
	Algorithm names are case-sensitive. If the MAC algorithm is		Algorithm names are case-sensitive. If the MAC algorithm is
	not understood by the client, the client MUST NOT use the MAC		not understood by the client, the client MUST NOT use the MAC
	credentials and continue as if no MAC credentials were issued.		credentials and continue as if no MAC credentials were issued.
	The MAC key identifier, MAC key, MAC algorithm strings MUST NOT		The MAC key identifier, MAC key, MAC algorithm strings MUST NOT
	include characters other than:		include characters other than:
	%x20-21 / %x23-5B / %x5D-7E		%x20-21 / %x23-5B / %x5D-7E
	skipping to change at page 7, line 22 ¶		skipping to change at page 6, line 47 ¶
	ext = "ext" "=" string-value		ext = "ext" "=" string-value
	mac = "mac" "=" string-value		mac = "mac" "=" string-value
	timestamp = 1*DIGIT		timestamp = 1*DIGIT
	string-value = ( <"> plain-string <"> ) / plain-string		string-value = ( <"> plain-string <"> ) / plain-string
	plain-string = 1*( %x20-21 / %x23-5B / %x5D-7E )		plain-string = 1*( %x20-21 / %x23-5B / %x5D-7E )
	The header attributes are set as follows:		The header attributes are set as follows:
	id		id
	REQUIRED. The MAC key identifier.		REQUIRED. The MAC key identifier.
	ts		ts
	REQUIRED. The request timestamp. The value MUST be a positive		REQUIRED. The request timestamp. The value MUST be a positive
	integer set by the client when making each request to the		integer set by the client when making each request to the
	number of seconds elapsed from a fixed point in time (e.g.		number of seconds elapsed from a fixed point in time (e.g.
	January 1, 1970 00:00:00 GMT). The value MUST NOT include		January 1, 1970 00:00:00 GMT). The value MUST NOT include
	leading zeros (e.g. "000273154346").		leading zeros (e.g. "000273154346").
	nonce		nonce
	REQUIRED. A unique string generated by the client. The value		REQUIRED. A unique string generated by the client. The value
	MUST be unique across all requests with the same timestamp and		MUST be unique across all requests with the same timestamp and
	MAC key identifier combination.		MAC key identifier combination.
	ext		ext
	OPTIONAL. A string used to include additional information		OPTIONAL. A string used to include additional information which
	which is covered by the request MAC. The content and format of		is covered by the request MAC. The content and format of the
	the string is beyond the scope of this specification.		string is beyond the scope of this specification.
	mac		mac
	REQUIRED. The HTTP request MAC as described in Section 3.2.		REQUIRED. The HTTP request MAC as described in Section 3.2.
	Attributes MUST NOT appear more than once. Attribute values are		Attributes MUST NOT appear more than once. Attribute values are
	limited to a subset of ASCII, which does not require escaping, as		limited to a subset of ASCII, which does not require escaping, as
	defined by the plain-string ABNF.		defined by the plain-string ABNF.
	3.2. Request MAC		3.2. Request MAC
	The client uses the MAC algorithm and the MAC key to calculate the		The client uses the MAC algorithm and the MAC key to calculate the
	request MAC. This specification defines two algorithms: "hmac-sha-1"		request MAC. This specification defines two algorithms: "hmac-sha-1"
	and "hmac-sha-256", and provides an extension registry for additional		and "hmac-sha-256", and provides an extension registry for additional
	algorithms.		algorithms.
	3.2.1. Normalized Request String		3.2.1. Normalized Request String
	The normalized request string is a consistent, reproducible		The normalized request string is a consistent, reproducible
	concatenation of several of the HTTP request elements into a single		concatenation of several of the HTTP request elements into a single
	string. By normalizing the request into a reproducible string, the		string. By normalizing the request into a reproducible string, the
	client and server can both calculate the request MAC over the exact		client and server can both calculate the request MAC over the exact
	same value.		same value.
	skipping to change at page 8, line 18 ¶		skipping to change at page 7, line 47 ¶
	concatenation of several of the HTTP request elements into a single		concatenation of several of the HTTP request elements into a single
	string. By normalizing the request into a reproducible string, the		string. By normalizing the request into a reproducible string, the
	client and server can both calculate the request MAC over the exact		client and server can both calculate the request MAC over the exact
	same value.		same value.
	The string is constructed by concatenating together, in order, the		The string is constructed by concatenating together, in order, the
	following HTTP request elements, each followed by a new line		following HTTP request elements, each followed by a new line
	character (%x0A):		character (%x0A):
	1. The timestamp value calculated for the request.		1. The timestamp value calculated for the request.
	2. The nonce value generated for the request.		2. The nonce value generated for the request.
	3. The HTTP request method in upper case. For example: "HEAD",		3. The HTTP request method in upper case. For example: "HEAD",
	"GET", "POST", etc.		"GET", "POST", etc.
	4. The HTTP request-URI as defined by [RFC2616] section 5.1.2.		4. The HTTP request-URI as defined by [RFC2616] section 5.1.2.
	5. The hostname included in the HTTP request using the "Host"		5. The hostname included in the HTTP request using the "Host"
	request header field in lower case.		request header field in lower case.
	6. The port as included in the HTTP request using the "Host" request		6. The port as included in the HTTP request using the "Host" request
	header field. If the header field does not include a port, the		header field. If the header field does not include a port, the
	default value for the scheme MUST be used (e.g. 80 for HTTP and		default value for the scheme MUST be used (e.g. 80 for HTTP and
	443 for HTTPS).		443 for HTTPS).
	7. The value of the "ext" "Authorization" request header field		7. The value of the "ext" "Authorization" request header field
	attribute if one was included in the request, otherwise, an empty		attribute if one was included in the request, otherwise, an empty
	string.		string.
	Each element is followed by a new line character (%x0A) including the		Each element is followed by a new line character (%x0A) including the
	last element and even when an element value is an empty string.		last element and even when an element value is an empty string.
	For example, the HTTP request:		For example, the HTTP request:
	POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b&c2&a3=2+q HTTP/1.1		POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b&c2&a3=2+q HTTP/1.1
	skipping to change at page 9, line 24 ¶		skipping to change at page 9, line 5 ¶
	"hmac-sha-1" uses the HMAC-SHA1 algorithm as defined in [RFC2104]:		"hmac-sha-1" uses the HMAC-SHA1 algorithm as defined in [RFC2104]:
	mac = HMAC-SHA1 (key, text)		mac = HMAC-SHA1 (key, text)
	Where:		Where:
	text		text
	is set to the value of the normalized request string as		is set to the value of the normalized request string as
	described in Section 3.2.1,		described in Section 3.2.1,
	key		key
	is set to the MAC key provided by the server, and		is set to the MAC key provided by the server, and
	mac		mac
	is used to set the value of the "mac" attribute, after the		is used to set the value of the "mac" attribute, after the
	result octet string is base64-encoded per [RFC2045] section		result octet string is base64-encoded per [RFC2045] section
	6.8.		6.8.
	3.2.3. hmac-sha-256		3.2.3. hmac-sha-256
	"hmac-sha-256" uses the HMAC algorithm as defined in [RFC2104]		"hmac-sha-256" uses the HMAC algorithm as defined in [RFC2104]
	together with the SHA-256 hash function defined in [NIST FIPS-180-3]:		together with the SHA-256 hash function defined in [NIST-FIPS-180-3]:
	mac = HMAC-SHA256 (key, text)		mac = HMAC-SHA256 (key, text)
	Where:		Where:
	text		text
	is set to the value of the normalize request string as		is set to the value of the normalize request string as
	described in Section 3.2.1,		described in Section 3.2.1,
	key		key
	is set to the MAC key provided by the server, and		is set to the MAC key provided by the server, and
	mac		mac
	is used to set the value of the "mac" attribute, after the		is used to set the value of the "mac" attribute, after the
	result octet string is base64-encoded per [RFC2045] section		result octet string is base64-encoded per [RFC2045] section
	6.8.		6.8.
	4. Verifying Requests		4. Verifying Requests
	skipping to change at page 10, line 18 ¶		skipping to change at page 9, line 43 ¶
	6.8.		6.8.
	4. Verifying Requests		4. Verifying Requests
	A server receiving an authenticated request validates it by		A server receiving an authenticated request validates it by
	performing the following REQUIRED steps:		performing the following REQUIRED steps:
	1. Recalculate the request MAC as described in Section 3.2 and		1. Recalculate the request MAC as described in Section 3.2 and
	compare the request MAC to the value received from the client via		compare the request MAC to the value received from the client via
	the "mac" attribute.		the "mac" attribute.
	2. Ensure that the combination of timestamp, nonce, and MAC key		2. Ensure that the combination of timestamp, nonce, and MAC key
	identifier received from the client has not been received before		identifier received from the client has not been received before
	in a previous request. The server MAY reject requests with stale		in a previous request. The server MAY reject requests with stale
	timestamps as described in Section 4.1.		timestamps as described in Section 4.1.
	3. Verify the scope and validity of the MAC credentials.		3. Verify the scope and validity of the MAC credentials.
	If the request fails verification, the server SHOULD respond using		If the request fails verification, the server SHOULD respond using
	the 401 (Unauthorized) HTTP status code and include the		the 401 (Unauthorized) HTTP status code and include the "WWW-
	"WWW-Authenticate" response header field as described in Section 4.2.		Authenticate" response header field as described in Section 4.2.
	4.1. Timestamp Verification		4.1. Timestamp Verification
	The timestamp, nonce, and MAC key identifier combination provide a		The timestamp, nonce, and MAC key identifier combination provide a
	unique identifier which enables the server to prevent replay attacks.		unique identifier which enables the server to prevent replay attacks.
	Without replay protection, an attacker can use a compromised (but		Without replay protection, an attacker can use a compromised (but
	otherwise valid and authenticated) request more than once, gaining		otherwise valid and authenticated) request more than once, gaining
	long term access to a protected resource.		long term access to a protected resource.
	Including a timestamp with the nonce removes the need to retain an		Including a timestamp with the nonce removes the need to retain an
	infinite number of nonce values for future checks, by enabling the		infinite number of nonce values for future checks, by enabling the
	server to restrict the time period after which a request with an old		server to restrict the time period after which a request with an old
	timestamp is rejected. If such a restriction is enforced, the server		timestamp is rejected. If such a restriction is enforced, the server
	skipping to change at page 12, line 7 ¶		skipping to change at page 11, line 18 ¶
	readable explanation why the access request was declined to assist		readable explanation why the access request was declined to assist
	the client developer in identifying the problem.		the client developer in identifying the problem.
	For example:		For example:
	HTTP/1.1 401 Unauthorized		HTTP/1.1 401 Unauthorized
	WWW-Authenticate: MAC error="The MAC credentials expired"		WWW-Authenticate: MAC error="The MAC credentials expired"
	5. Use with OAuth 2.0		5. Use with OAuth 2.0
	OAuth 2.0 ([I-D.ietf-oauth-v2]) defines an extensible token-based		OAuth 2.0 ([RFC6749]) defines an extensible token-based
	authentication framework. The MAC authentication scheme can be used		authentication framework. The MAC authentication scheme can be used
	to make OAuth-based requests by issuing MAC-type access tokens.		to make OAuth-based requests by issuing MAC-type access tokens.
	This specification does not define methods for the client to		This specification does not define methods for the client to
	specifically request a MAC-type token from the authorization server.		specifically request a MAC-type token from the authorization server.
	Additionally, it does not include any discovery facilities for		Additionally, it does not include any discovery facilities for
	identifying which HMAC algorithms are supported by a resource server,		identifying which HMAC algorithms are supported by a resource server,
	or how the client may go about obtaining MAC access tokens for any		or how the client may go about obtaining MAC access tokens for any
	given protected resource.		given protected resource.
	5.1. Issuing MAC-Type Access Tokens		5.1. Issuing MAC-Type Access Tokens
	Authorization servers issuing MAC-type access tokens MUST include the		Authorization servers issuing MAC-type access tokens MUST include the
	following parameters whenever a response includes the "access_token"		following parameters whenever a response includes the "access_token"
	parameter:		parameter:
	access_token		access_token
	REQUIRED. The MAC key identifier.		REQUIRED. The MAC key identifier.
	mac_key		mac_key
	REQUIRED. The MAC key.		REQUIRED. The MAC key.
	mac_algorithm		mac_algorithm
	REQUIRED. The MAC algorithm used to calculate the request MAC.		REQUIRED. The MAC algorithm used to calculate the request MAC.
	Value MUST be one of "hmac-sha-1", "hmac-sha-256", or a		Value MUST be one of "hmac-sha-1", "hmac-sha-256", or a
	registered extension algorithm name as described in		registered extension algorithm name as described in Section
	Section 7.1.		7.1.
	For example:		For example:
	HTTP/1.1 200 OK		HTTP/1.1 200 OK
	Content-Type: application/json		Content-Type: application/json
	Cache-Control: no-store		Cache-Control: no-store
	{		{
	"access_token":"SlAV32hkKG",		"access_token":"SlAV32hkKG",
	"token_type":"mac",		"token_type":"mac",
	skipping to change at page 15, line 10 ¶		skipping to change at page 14, line 20 ¶
	while the system waits for new entropy or else in weak (easily		while the system waits for new entropy or else in weak (easily
	guessable) MAC keys. When implementing this protocol, servers should		guessable) MAC keys. When implementing this protocol, servers should
	consider which of these presents a more serious risk for their		consider which of these presents a more serious risk for their
	application and design accordingly.		application and design accordingly.
	6.7. Timing Attacks		6.7. Timing Attacks
	This specification makes use of HMACs, for which a signature		This specification makes use of HMACs, for which a signature
	verification involves comparing the received MAC string to the		verification involves comparing the received MAC string to the
	expected one. If the string comparison operator operates in		expected one. If the string comparison operator operates in
	observably different times depending on inputs, e.g. because it		observably different times depending on inputs, e.g. because it
	compares the strings character by character and returns a negative		compares the strings character by character and returns a negative
	result as soon as two characters fail to match, then it may be		result as soon as two characters fail to match, then it may be
	possible to use this timing information to determine the expected		possible to use this timing information to determine the expected
	MAC, character by character.		MAC, character by character.
	Service implementers are encouraged to use fixed-time string		Service implementers are encouraged to use fixed-time string
	comparators for MAC verification.		comparators for MAC verification.
	6.8. CSRF Attacks		6.8. CSRF Attacks
	A Cross-Site Request Forgery attack occurs when a site, evil.com,		A Cross-Site Request Forgery attack occurs when a site, evil.com,
	initiates within the victim's browser the loading of a URL from or		initiates within the victim's browser the loading of a URL from or
	the posting of a form to a web site where a side-effect will occur,		the posting of a form to a web site where a side-effect will occur,
	e.g. transfer of money, change of status message, etc. To prevent		e.g. transfer of money, change of status message, etc. To prevent
	this kind of attack, web sites may use various techniques to		this kind of attack, web sites may use various techniques to
	determine that the originator of the request is indeed the site		determine that the originator of the request is indeed the site
	itself, rather than a third party. The classic approach is to		itself, rather than a third party. The classic approach is to
	include, in the set of URL parameters or form content, a nonce		include, in the set of URL parameters or form content, a nonce
	generated by the server and tied to the user's session, which		generated by the server and tied to the user's session, which
	indicates that only the server could have triggered the action.		indicates that only the server could have triggered the action.
	Recently, the Origin HTTP header has been proposed and deployed in		Recently, the Origin HTTP header has been proposed and deployed in
	some browsers. This header indicates the scheme, host, and port of		some browsers. This header indicates the scheme, host, and port of
	the originator of a request. Some web applications may use this		the originator of a request. Some web applications may use this
	skipping to change at page 15, line 46 ¶		skipping to change at page 15, line 4 ¶
	To keep this specification simple, HTTP headers are not part of the		To keep this specification simple, HTTP headers are not part of the
	string to be MAC'ed. As a result, MAC authentication cannot defend		string to be MAC'ed. As a result, MAC authentication cannot defend
	against header spoofing, and a web site that uses the Host header to		against header spoofing, and a web site that uses the Host header to
	defend against CSRF attacks cannot use MAC authentication to defend		defend against CSRF attacks cannot use MAC authentication to defend
	against active network attackers. Sites that want the full		against active network attackers. Sites that want the full
	protection of MAC Authentication should use traditional, cookie-tied		protection of MAC Authentication should use traditional, cookie-tied
	CSRF defenses.		CSRF defenses.
	6.9. Coverage Limitations		6.9. Coverage Limitations
	The normalized request string has been designed to support the		The normalized request string has been designed to support the
	authentication methods defined in this specification. Those		authentication methods defined in this specification. Those
	designing additional methods, should evaluated the compatibility of		designing additional methods, should evaluated the compatibility of
	the normalized request string with their security requirements.		the normalized request string with their security requirements.
	Since the normalized request string does not cover the entire HTTP		Since the normalized request string does not cover the entire HTTP
	request, servers should employ additional mechanisms to protect such		request, servers should employ additional mechanisms to protect such
	elements.		elements.
	The request MAC does not cover entity-header fields which can often		The request MAC does not cover entity-header fields which can often
	affect how the request body is interpreted by the server (i.e.		affect how the request body is interpreted by the server (i.e.
	Content-Type). If the server behavior is influenced by the presence		Content-Type). If the server behavior is influenced by the presence
	or value of such header fields, an attacker can manipulate the		or value of such header fields, an attacker can manipulate the
	request header without being detected.		request header without being detected.
	7. IANA Considerations		7. IANA Considerations
	7.1. The HTTP MAC Authentication Scheme Algorithm Registry		7.1. The HTTP MAC Authentication Scheme Algorithm Registry
	This specification establishes the HTTP MAC authentication scheme		This specification establishes the HTTP MAC authentication scheme
	algorithm registry.		algorithm registry.
	Additional MAC algorithms are registered on the advice of one or more		Additional MAC algorithms are registered on the advice of one or more
	Designated Experts (appointed by the IESG or their delegate), with a		Designated Experts (appointed by the IESG or their delegate), with a
	Specification Required (using terminology from [RFC5226]). However,		Specification Required (using terminology from [RFC5226]). However,
	to allow for the allocation of values prior to publication, the		to allow for the allocation of values prior to publication, the
	Designated Expert(s) may approve registration once they are satisfied		Designated Expert(s) may approve registration once they are satisfied
	that such a specification will be published.		that such a specification will be published.
	Registration requests should be sent to the [TBD]@ietf.org mailing		Registration requests should be sent to the [TBD]@ietf.org mailing
	list for review and comment, with an appropriate subject (e.g.,		list for review and comment, with an appropriate subject (e.g.,
	"Request for MAC Algorithm: example"). [[ Note to RFC-EDITOR: The		"Request for MAC Algorithm: example"). [[ Note to RFC-EDITOR: The
	name of the mailing list should be determined in consultation with		name of the mailing list should be determined in consultation with
	the IESG and IANA. Suggested name: http-mac-ext-review. ]]		the IESG and IANA. Suggested name: http-mac-ext-review. ]]
	Within at most 14 days of the request, the Designated Expert(s) will		Within at most 14 days of the request, the Designated Expert(s) will
	either approve or deny the registration request, communicating this		either approve or deny the registration request, communicating this
	decision to the review list and IANA. Denials should include an		decision to the review list and IANA. Denials should include an
	explanation and, if applicable, suggestions as to how to make the		explanation and, if applicable, suggestions as to how to make the
	request successful.		request successful.
	Decisions (or lack thereof) made by the Designated Expert can be		Decisions (or lack thereof) made by the Designated Expert can be
	first appealed to Application Area Directors (contactable using		first appealed to Application Area Directors (contactable using app-
	app-ads@tools.ietf.org email address or directly by looking up their		ads@tools.ietf.org email address or directly by looking up their
	email addresses on http://www.iesg.org/ website) and, if the		email addresses on http://www.iesg.org/ website) and, if the
	appellant is not satisfied with the response, to the full IESG (using		appellant is not satisfied with the response, to the full IESG (using
	the iesg@iesg.org mailing list).		the iesg@iesg.org mailing list).
	IANA should only accept registry updates from the Designated		IANA should only accept registry updates from the Designated
	Expert(s), and should direct all requests for registration to the		Expert(s), and should direct all requests for registration to the
	review mailing list.		review mailing list.
	7.1.1. Registration Template		7.1.1. Registration Template
	Algorithm name:		Algorithm name:
	The name requested (e.g., "example").		The name requested (e.g., "example").
	Change controller:		Change controller:
	For standards-track RFCs, state "IETF". For others, give the name		For standards-track RFCs, state "IETF". For others, give the name
	of the responsible party. Other details (e.g., postal address,		of the responsible party. Other details (e.g., postal address,
	e-mail address, home page URI) may also be included.		e-mail address, home page URI) may also be included.
	Specification document(s):		Specification document(s):
	Reference to document that specifies the algorithm, preferably		Reference to document that specifies the algorithm, preferably
	including a URI that can be used to retrieve a copy of the		including a URI that can be used to retrieve a copy of the
	document. An indication of the relevant sections may also be		document. An indication of the relevant sections may also be
	included, but is not required.		included, but is not required.
	7.1.2. Initial Registry Contents		7.1.2. Initial Registry Contents
	The HTTP MAC authentication scheme algorithm registry's initial		The HTTP MAC authentication scheme algorithm registry's initial
	contents are:		contents are:
	skipping to change at page 17, line 41 ¶		skipping to change at page 16, line 44 ¶
	7.2. OAuth Access Token Type Registration		7.2. OAuth Access Token Type Registration
	This specification registers the following access token type in the		This specification registers the following access token type in the
	OAuth Access Token Type Registry.		OAuth Access Token Type Registry.
	7.2.1. The "mac" OAuth Access Token Type		7.2.1. The "mac" OAuth Access Token Type
	Type name:		Type name:
	mac		mac
	Additional Token Endpoint Response Parameters:		Additional Token Endpoint Response Parameters:
	secret, algorithm		secret, algorithm
	HTTP Authentication Scheme(s):		HTTP Authentication Scheme(s):
	MAC		MAC
	Change controller:		Change controller:
	IETF		IETF
	Specification document(s):		Specification document(s):
	[[ this document ]]		[[ this document ]]
	7.3. OAuth Parameters Registration		7.3. OAuth Parameters Registration
	This specification registers the following parameters in the OAuth		This specification registers the following parameters in the OAuth
	Parameters Registry established by [I-D.ietf-oauth-v2].		Parameters Registry established by [RFC6749].
	7.3.1. The "mac_key" OAuth Parameter		7.3.1. The "mac_key" OAuth Parameter
	Parameter name: mac_key		Parameter name: mac_key
	Parameter usage location: authorization response, token response
	Change controller: IETF		Parameter usage location: authorization response, token response
	Specification document(s): [[ this document ]]
	Related information: None		Change controller: IETF
			Specification document(s): [[ this document ]]
			Related information: None
	7.3.2. The "mac_algorithm" OAuth Parameter		7.3.2. The "mac_algorithm" OAuth Parameter
	Parameter name: mac_algorithm		Parameter name: mac_algorithm
	Parameter usage location: authorization response, token response
	Change controller: IETF
	Specification document(s): [[ this document ]]
	Related information: None
	8. Acknowledgments		Parameter usage location: authorization response, token response
			Change controller: IETF
			Specification document(s): [[ this document ]]
			Related information: None
			8. Contributors
			This document is based on OAuth 1.0 and we would like to thank Eran
			Hammer-Lahav for his work on incorporating the ideas into OAuth 2.0.
			9. Acknowledgments
	The author would like to thank Ben Adida, Adam Barth, Phil Hunt,		The author would like to thank Ben Adida, Adam Barth, Phil Hunt,
	Rasmus Lerdorf, James Manger, William Mills, Scott Renfro, Justin		Rasmus Lerdorf, James Manger, William Mills, Scott Renfro, Justin
	Richer, Toby White, Peter Wolanin, and Skylar Woodward for their		Richer, Toby White, Peter Wolanin, and Skylar Woodward for their
	contributions, suggestions, and feedback.		contributions, suggestions, and feedback.
	9. References		10. References
	9.1. Normative References		10.1. Normative References
	[I-D.ietf-httpbis-p1-messaging]		[10] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
	Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,		(HTTP/1.1): Message Syntax and Routing", Internet-Draft
	Masinter, L., Leach, P., Berners-Lee, T., and J. Reschke,		draft-ietf-httpbis-p1-messaging-21, October 2012.
	"HTTP/1.1, part 1: URIs, Connections, and Message
	Parsing", draft-ietf-httpbis-p1-messaging-13 (work in
	progress), March 2011.
	[I-D.ietf-oauth-v2]		[11] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC
	Hammer-Lahav, E., Recordon, D., and D. Hardt, "The OAuth		6749, October 2012.
	2.0 Authorization Protocol", draft-ietf-oauth-v2-15 (work
	in progress), April 2011.
	[NIST FIPS-180-3]		[12] Hors, A., Raggett, D. and I. Jacobs, "HTML 4.01
	National Institute of Standards and Technology, "Secure		Specification", World Wide Web Consortium Recommendation
	Hash Standard (SHS). FIPS PUB 180-3, October 2008".		REC-html401-19991224, December 1999, <http://www.w3.org/TR
			/1999/REC-html401-19991224>.
	[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail		[13] National Institute of Standards and Technology, "Secure
			Hash Standard (SHS). FIPS PUB 180-3, October 2008", .
			[1] Bradner, S., "Key words for use in RFCs to Indicate
			Requirement Levels", BCP 14, RFC 2119, March 1997.
			[2] Freed, N. and N.S. Borenstein, "Multipurpose Internet Mail
	Extensions (MIME) Part One: Format of Internet Message		Extensions (MIME) Part One: Format of Internet Message
	Bodies", RFC 2045, November 1996.		Bodies", RFC 2045, November 1996.
	[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-		[3] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-
	Hashing for Message Authentication", RFC 2104,		Hashing for Message Authentication", RFC 2104, February
	February 1997.		1997.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,		[4] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
	Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext		Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
	Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.		Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
	[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,		[5] Franks, J., Hallam-Baker, P.M., Hostetler, J.L., Lawrence,
	Leach, P., Luotonen, A., and L. Stewart, "HTTP		S.D., Leach, P.J., Luotonen, A. and L. Stewart, "HTTP
	Authentication: Basic and Digest Access Authentication",		Authentication: Basic and Digest Access Authentication",
	RFC 2617, June 1999.		RFC 2617, June 1999.
	[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform		[6] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
	Resource Identifier (URI): Generic Syntax", STD 66,		Resource Identifier (URI): Generic Syntax", STD 66, RFC
	RFC 3986, January 2005.		3986, January 2005.
	[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an		[7] Narten, T. and H. Alvestrand, "Guidelines for Writing an
	IANA Considerations Section in RFCs", BCP 26, RFC 5226,		IANA Considerations Section in RFCs", BCP 26, RFC 5226,
	May 2008.		May 2008.
	[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security		[8] Dierks, T. and E. Rescorla, "The Transport Layer Security
	(TLS) Protocol Version 1.2", RFC 5246, August 2008.		(TLS) Protocol Version 1.2", RFC 5246, August 2008.
	[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,		[9] Barth, A., "HTTP State Management Mechanism", RFC 6265,
	April 2011.		April 2011.
	[W3C.REC-html401-19991224]		10.2. Informative References
	Hors, A., Raggett, D., and I. Jacobs, "HTML 4.01
	Specification", World Wide Web Consortium
	Recommendation REC-html401-19991224, December 1999,
	<http://www.w3.org/TR/1999/REC-html401-19991224>.
	9.2. Informative References		[1] Tschofenig, H. and P. Hunt, "OAuth 2.0 Security: Going
			Beyond Bearer Tokens", Internet-Draft draft-tschofenig-
			oauth-security-00, September 2012.
	[RFC5849] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,		[2] Bradley, J., Hunt, P., Nadalin, A. and H. Tschofenig, "The
			OAuth 2.0 Authorization Framework: Holder-of-the-Key Token
			Usage", Internet-Draft draft-tschofenig-oauth-hotk-01,
			July 2012.
			[3] Hammer-Lahav, E., "The OAuth 1.0 Protocol", RFC 5849,
	April 2010.		April 2010.
	Author's Address		Authors' Addresses
	Eran Hammer-Lahav (editor)		Justin Richer, editor
			The MITRE Corporation
	Email: eran@hueniverse.com		Email: jricher@mitre.org
	URI: http://hueniverse.com
			William Mills, editor
			Yahoo! Inc.
			Email: wmills@yahoo-inc.com
			Hannes Tschofenig, editor
			Nokia Siemens Networks
			Linnoitustie 6
			Espoo, 02600
			Finland
			Phone: +358 (50) 4871445
			Email: Hannes.Tschofenig@gmx.net
			URI: http://www.tschofenig.priv.at
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