Network Working Group E. Hammer-Lahav, Ed. Internet-Draft B. Cook Intended status: Standards Track September 30, 2008 Expires: April 3, 2009 OAuth: HTTP Authorization Delegation Protocol draft-hammer-oauth-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 3, 2009. Abstract This document specifies OAuth, an HTTP authorization delegation protocol for accessing protected resources. Hammer-Lahav & Cook Expires April 3, 2009 [Page 1] Internet-Draft OAuth Authorization Protocol September 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Documentation and Registration . . . . . . . . . . . . . . . . 5 4.1. Request URLs . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Service Providers . . . . . . . . . . . . . . . . . . . . 6 4.3. Consumers . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. Consumer Request Parameters . . . . . . . . . . . . . . . 7 5.2. Service Provider Response Parameters . . . . . . . . . . 7 5.3. OAuth HTTP Authorization Scheme . . . . . . . . . . . . . 7 5.3.1. Authorization Header . . . . . . . . . . . . . . . . . 7 5.3.2. WWW-Authenticate Header . . . . . . . . . . . . . . . 8 6. Authenticating with OAuth . . . . . . . . . . . . . . . . . . 8 6.1. Obtaining an Unauthorized Request Token . . . . . . . . . 9 6.1.1. Consumer Obtains a Request Token . . . . . . . . . . . 9 6.1.2. Service Provider Issues an Unauthorized Request Token . . . . . . . . . . . . . . . . . . . . . . . . 10 6.2. Obtaining User Authorization . . . . . . . . . . . . . . 10 6.2.1. Consumer Directs the User to the Service Provider . . 10 6.2.2. Service Provider Authenticates the User and Obtains Consent . . . . . . . . . . . . . . . . . . . 11 6.2.3. Service Provider Directs the User Back to the Consumer . . . . . . . . . . . . . . . . . . . . . . . 12 6.3. Obtaining an Access Token . . . . . . . . . . . . . . . . 12 6.3.1. Consumer Requests an Access Token . . . . . . . . . . 12 6.3.2. Service Provider Grants an Access Token . . . . . . . 13 7. Accessing Protected Resources . . . . . . . . . . . . . . . . 14 8. Nonce and Timestamp . . . . . . . . . . . . . . . . . . . . . 14 9. Signing Requests . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. Signature Base String . . . . . . . . . . . . . . . . . . 15 9.1.1. Parameter Encoding . . . . . . . . . . . . . . . . . . 15 9.1.2. Normalize Request Parameters . . . . . . . . . . . . . 16 9.1.3. Construct Request URL . . . . . . . . . . . . . . . . 17 9.1.4. Concatenate Request Elements . . . . . . . . . . . . . 17 9.2. HMAC-SHA1 . . . . . . . . . . . . . . . . . . . . . . . . 17 9.2.1. Generating Signature . . . . . . . . . . . . . . . . . 18 9.2.2. Verifying Signature . . . . . . . . . . . . . . . . . 18 9.3. RSA-SHA1 . . . . . . . . . . . . . . . . . . . . . . . . 18 9.3.1. Generating Signature . . . . . . . . . . . . . . . . . 18 9.3.2. Verifying Signature . . . . . . . . . . . . . . . . . 18 9.4. PLAINTEXT . . . . . . . . . . . . . . . . . . . . . . . . 19 9.4.1. Generating Signature . . . . . . . . . . . . . . . . . 19 9.4.2. Verifying Signature . . . . . . . . . . . . . . . . . 19 10. HTTP Response Codes . . . . . . . . . . . . . . . . . . . . . 19 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 Hammer-Lahav & Cook Expires April 3, 2009 [Page 2] Internet-Draft OAuth Authorization Protocol September 2008 12. Security Considerations . . . . . . . . . . . . . . . . . . . 20 12.1. Credentials and Token Exchange . . . . . . . . . . . . . 20 12.2. RSA-SHA1 Signature Method . . . . . . . . . . . . . . . . 20 12.3. PLAINTEXT Signature Method . . . . . . . . . . . . . . . 20 12.4. Confidentiality of Requests . . . . . . . . . . . . . . . 21 12.5. Spoofing by Counterfeit Servers . . . . . . . . . . . . . 21 12.6. Proxying and Caching of Authenticated Content . . . . . . 21 12.7. Plaintext Storage of Credentials . . . . . . . . . . . . 21 12.8. Secrecy of the Consumer Secret . . . . . . . . . . . . . 22 12.9. Phishing Attacks . . . . . . . . . . . . . . . . . . . . 22 12.10. Scoping of Access Requests . . . . . . . . . . . . . . . 22 12.11. Entropy of Secrets . . . . . . . . . . . . . . . . . . . 22 12.12. Denial of Service / Resource Exhaustion Attacks . . . . . 23 12.13. Cryptographic Attacks . . . . . . . . . . . . . . . . . . 24 12.14. Signature Base String Compatibility . . . . . . . . . . . 24 Appendix A. Appendix A - Protocol Example . . . . . . . . . . 24 Appendix A.1. Documentation and Registration . . . . . . . . . . 24 Appendix A.2. Obtaining a Request Token . . . . . . . . . . . . 25 Appendix A.3. Requesting User Authorization . . . . . . . . . . 26 Appendix A.4. Obtaining an Access Token . . . . . . . . . . . . 26 Appendix A.5. Accessing Protected Resources . . . . . . . . . . 26 Appendix A.5.1. Generating Signature Base String . . . . . . . . . 26 Appendix A.5.2. Calculating Signature Value . . . . . . . . . . . 27 Appendix A.5.3. Requesting Protected Resource . . . . . . . . . . 27 Appendix B. Contributors . . . . . . . . . . . . . . . . . . . 28 13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29 13.1. Normative References . . . . . . . . . . . . . . . . . . 29 13.2. Informative References . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30 Intellectual Property and Copyright Statements . . . . . . . . . . 31 Hammer-Lahav & Cook Expires April 3, 2009 [Page 3] Internet-Draft OAuth Authorization Protocol September 2008 1. Introduction The OAuth protocol enables websites or applications (Consumers) to access Protected Resources from a web service (Service Provider) via an API, without requiring Users to disclose their Service Provider credentials to the Consumers. More generally, OAuth creates a freely-implementable and generic methodology for API authentication. An example use case is allowing printing service printer.example.com (the Consumer), to access private photos stored on photos.example.net (the Service Provider) without requiring Users to provide their photos.example.net credentials to printer.example.com. OAuth does not require a specific user interface or interaction pattern, nor does it specify how Service Providers authenticate Users, making the protocol ideally suited for cases where authentication credentials are unavailable to the Consumer, such as with OpenID. OAuth aims to unify the experience and implementation of delegated web service authentication into a single, community-driven protocol. OAuth builds on existing protocols and best practices that have been independently implemented by various websites. An open standard, supported by large and small providers alike, promotes a consistent and trusted experience for both application developers and the users of those applications. Discussion of this draft should take place on the OAuth mailing list located at oauth@googlegroups.com. To join the list, visit http://groups.google.com/group/oauth (you will be asked to provide a reason to join solely as a spam filter). 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Definitions Service Provider: A web application that allows access via OAuth. User: An individual who has an account with the Service Provider. Hammer-Lahav & Cook Expires April 3, 2009 [Page 4] Internet-Draft OAuth Authorization Protocol September 2008 Consumer: A website or application that uses OAuth to access the Service Provider on behalf of the User. Protected Resource(s): Data controlled by the Service Provider, which the Consumer can access through authentication. Consumer Developer: An individual or organization that implements a Consumer. Consumer Key: A value used by the Consumer to identify itself to the Service Provider. Consumer Secret: A secret used by the Consumer to establish ownership of the Consumer Key. Request Token: A value used by the Consumer to obtain authorization from the User, and exchanged for an Access Token. Access Token: A value used by the Consumer to gain access to the Protected Resources on behalf of the User, instead of using the User's Service Provider credentials. Token Secret: A secret used by the Consumer to establish ownership of a given Token. OAuth Protocol Parameters: Parameters with names beginning with "oauth_". 4. Documentation and Registration OAuth includes a Consumer Key and matching Consumer Secret that together authenticate the Consumer (as opposed to the User) with the Service Provider. Consumer-specific identification allows the Service Provider to vary access levels to Consumers (such as un- throttled access to resources). Service Providers SHOULD NOT rely on the Consumer Secret as a method to verify the Consumer identity, unless the Consumer Secret is known to be inaccessible to anyone other than the Consumer and the Service Provider. The Consumer Secret MAY be an empty string (for example when no Consumer verification is needed, or when verification is achieved through other means such as RSA). 4.1. Request URLs OAuth defines three request URLs: Hammer-Lahav & Cook Expires April 3, 2009 [Page 5] Internet-Draft OAuth Authorization Protocol September 2008 Request Token URL: The URL used to obtain an unauthorized Request Token, described in Section 6.1. User Authorization URL: The URL used to obtain User authorization for Consumer access, described in Section 6.2. Access Token URL: The URL used to exchange the User-authorized Request Token for an Access Token, described in Section 6.3. The three URLs MUST include scheme, authority, and path, and MAY include query and fragment as defined by [RFC3986] section 3. The request URL query MUST NOT contain any OAuth Protocol Parameters. For example: http://sp.example.com/authorize 4.2. Service Providers The Service Provider's responsibility is to enable Consumer Developers to establish a Consumer Key and Consumer Secret. The process and requirements for provisioning these are entirely up to the Service Providers. The Service Provider's documentation includes: 1. The URLs (Section 4.1) the Consumer will use when making OAuth requests, and the HTTP methods (i.e. GET, POST, etc.) used in the Request Token URL and Access Token URL. 2. Signature methods supported by the Service Provider. 3. Any additional request parameters that the Service Provider requires in order to obtain a Token. Service Provider specific parameters MUST NOT begin with "oauth_". 4.3. Consumers The Consumer Developer MUST establish a Consumer Key and a Consumer Secret with the Service Provider. The Consumer Developer MAY also be required to provide additional information to the Service Provider upon registration. 5. Parameters OAuth Protocol Parameter names and values are case sensitive. Each OAuth Protocol Parameters MUST NOT appear more than once per request, and are REQUIRED unless otherwise noted. Hammer-Lahav & Cook Expires April 3, 2009 [Page 6] Internet-Draft OAuth Authorization Protocol September 2008 5.1. Consumer Request Parameters OAuth Protocol Parameters are sent from the Consumer to the Service Provider in one of three methods, in order of decreasing preference: 1. In the HTTP "Authorization" header as defined in OAuth HTTP Authorization Scheme (Section 5.3). 2. As the HTTP request body with a " content-type " of "application/x-www-form-urlencoded" as defined by [W3C.REC-html40-19980424]. 3. Added to the URLs in the query part (as defined by [RFC3986] section 3). In addition to these defined methods, future extensions may describe alternate methods for sending the OAuth Protocol Parameters. The methods for sending other request parameters are left undefined, but SHOULD NOT use the OAuth HTTP Authorization Scheme (Section 5.3) header. 5.2. Service Provider Response Parameters Response parameters such as Tokens and Token Secrets are sent by the Service Provider to the Consumer in the HTTP response body using the "application/x-www-form-urlencoded" content type as defined by [W3C.REC-html40-19980424]. For example: oauth_token=ab3cd9j4ks73hf7g&oauth_token_secret=xyz4992k83j47x0b 5.3. OAuth HTTP Authorization Scheme This section defines an [RFC2617] extension to support OAuth. It uses the standard HTTP "Authorization" and "WWW-Authenticate" headers to pass OAuth Protocol Parameters. It is RECOMMENDED that Service Providers accept the HTTP "Authorization" header. Consumers SHOULD be able to send OAuth Protocol Parameters in the OAuth "Authorization" header. The extension auth-scheme (as defined by [RFC2617]) is "OAuth" and is case-insensitive. 5.3.1. Authorization Header The OAuth Protocol Parameters are sent in the "Authorization" header the following way: Hammer-Lahav & Cook Expires April 3, 2009 [Page 7] Internet-Draft OAuth Authorization Protocol September 2008 1. Parameter names and values are encoded per Parameter Encoding (Section 9.1.1). 2. For each parameter, the name is immediately followed by an '=' character (ASCII code 61), a '"' character (ASCII code 34), the parameter value (MAY be empty), and another '"' character (ASCII code 34). 3. Parameters are separated by a comma character (ASCII code 44) and OPTIONAL linear whitespace per [RFC2617]. 4. The OPTIONAL "realm" parameter is added and interpreted per [RFC2617], section 1.2. For example: Authorization: OAuth realm="http://sp.example.com/", oauth_consumer_key="0685bd9184jfhq22", oauth_token="ad180jjd733klru7", oauth_signature_method="HMAC-SHA1", oauth_signature="wOJIO9A2W5mFwDgiDvZbTSMK%2FPY%3D", oauth_timestamp="137131200", oauth_nonce="4572616e48616d6d65724c61686176", oauth_version="1.0" 5.3.2. WWW-Authenticate Header Service Providers MAY indicate their support for the extension by returning the OAuth HTTP "WWW-Authenticate" header upon Consumer requests for Protected Resources. As per [RFC2617] such a response MAY include additional HTTP "WWW-Authenticate" headers: For example: WWW-Authenticate: OAuth realm="http://sp.example.com/" The realm parameter defines a protection realm per [RFC2617], section 1.2. 6. Authenticating with OAuth OAuth authentication is the process in which Users grant access to their Protected Resources without sharing their credentials with the Consumer. OAuth uses Tokens generated by the Service Provider instead of the User's credentials in Protected Resources requests. The process uses two Token types: Hammer-Lahav & Cook Expires April 3, 2009 [Page 8] Internet-Draft OAuth Authorization Protocol September 2008 Request Token: Used by the Consumer to ask the User to authorize access to the Protected Resources. The User-authorized Request Token is exchanged for an Access Token, MUST only be used once, and MUST NOT be used for any other purpose. It is RECOMMENDED that Request Tokens have a limited lifetime. Access Token: Used by the Consumer to access the Protected Resources on behalf of the User. Access Tokens MAY limit access to certain Protected Resources, and MAY have a limited lifetime. Service Providers SHOULD allow Users to revoke Access Tokens. Only the Access Token SHALL be used to access the Protect Resources. OAuth Authentication is done in three steps: 1. The Consumer obtains an unauthorized Request Token. 2. The User authorizes the Request Token. 3. The Consumer exchanges the Request Token for an Access Token. 6.1. Obtaining an Unauthorized Request Token The Consumer obtains an unauthorized Request Token by asking the Service Provider to issue a Token. The Request Token's sole purpose is to receive User approval and can only be used to obtain an Access Token. The Request Token process goes as follows: 6.1.1. Consumer Obtains a Request Token To obtain a Request Token, the Consumer sends an HTTP request to the Service Provider's Request Token URL. The Service Provider documentation specifies the HTTP method for this request, and HTTP POST is RECOMMENDED. The request MUST be signed and contains the following parameters: oauth_consumer_key: The Consumer Key. oauth_signature_method: The signature method the Consumer used to sign the request. oauth_signature: The signature as defined in Signing Requests (Section 9). oauth_timestamp: As defined in Nonce and Timestamp (Section 8). Hammer-Lahav & Cook Expires April 3, 2009 [Page 9] Internet-Draft OAuth Authorization Protocol September 2008 oauth_nonce: As defined in Nonce and Timestamp (Section 8). oauth_version: OPTIONAL. If present, value MUST be " 1.0 ". Service Providers MUST assume the protocol version to be "1.0" if this parameter is not present. Service Providers' response to non-"1.0" value is left undefined. Additional parameters: Any additional parameters, as defined by the Service Provider. 6.1.2. Service Provider Issues an Unauthorized Request Token The Service Provider verifies the signature and Consumer Key. If successful, it generates a Request Token and Token Secret and returns them to the Consumer in the HTTP response body as defined in Service Provider Response Parameters (Section 5.2). The Service Provider MUST ensure the Request Token cannot be exchanged for an Access Token until the User successfully grants access in Obtaining User Authorization (Section 6.2). The response contains the following parameters: oauth_token: The Request Token. oauth_token_secret: The Token Secret. Additional parameters: Any additional parameters, as defined by the Service Provider. If the request fails verification or is rejected for other reasons, the Service Provider SHOULD respond with the appropriate response code as defined in HTTP Response Codes (Section 10). The Service Provider MAY include some further details about why the request was rejected in the HTTP response body as defined in Service Provider Response Parameters (Section 5.2). 6.2. Obtaining User Authorization The Consumer cannot use the Request Token until it has been authorized by the User. Obtaining User authorization includes the following steps: 6.2.1. Consumer Directs the User to the Service Provider In order for the Consumer to be able to exchange the Request Token for an Access Token, the Consumer MUST obtain approval from the User by directing the User to the Service Provider. The Consumer constructs an HTTP GET request to the Service Provider's User Hammer-Lahav & Cook Expires April 3, 2009 [Page 10] Internet-Draft OAuth Authorization Protocol September 2008 Authorization URL with the following parameter: oauth_token: OPTIONAL. The Request Token obtained in the previous step. The Service Provider MAY declare this parameter as REQUIRED, or accept requests to the User Authorization URL without it, in which case it will prompt the User to enter it manually. oauth_callback: OPTIONAL. The Consumer MAY specify a URL the Service Provider will use to redirect the User back to the Consumer when Obtaining User Authorization (Section 6.2) is complete. Additional parameters: Any additional parameters, as defined by the Service Provider. Once the request URL has been constructed the Consumer redirects the User to the URL via the User's web browser. If the Consumer is incapable of automatic HTTP redirection, the Consumer SHALL notify the User how to manually go to the constructed request URL. Note: If a Service Provider knows a Consumer to be running on a mobile device or set-top box, the Service Provider SHOULD ensure that the User Authorization URL and Request Token are suitable for manual entry. 6.2.2. Service Provider Authenticates the User and Obtains Consent The Service Provider verifies the User's identity and asks for consent as detailed. OAuth does not specify how the Service Provider authenticates the User. However, it does define a set of REQUIRED steps: o The Service Provider MUST first verify the User's identity before asking for consent. It MAY prompt the User to sign in if the User has not already done so. o The Service Provider presents to the User information about the Consumer requesting access (as registered by the Consumer Developer). The information includes the duration of the access and the Protected Resources provided. The information MAY include other details specific to the Service Provider. o The User MUST grant or deny permission for the Service Provider to give the Consumer access to the Protected Resources on behalf of the User. If the User denies the Consumer access, the Service Provider MUST NOT allow access to the Protected Resources. When displaying any identifying information about the Consumer to the Hammer-Lahav & Cook Expires April 3, 2009 [Page 11] Internet-Draft OAuth Authorization Protocol September 2008 User based on the Consumer Key, the Service Provider MUST inform the User if it is unable to assure the Consumer's true identity. The method in which the Service Provider informs the User and the quality of the identity assurance is beyond the scope of this specification. 6.2.3. Service Provider Directs the User Back to the Consumer After the User authenticates with the Service Provider and grants permission for Consumer access, the Consumer MUST be notified that the Request Token has been authorized and ready to be exchanged for an Access Token. If the User denies access, the Consumer MAY be notified that the Request Token has been revoked. If the Consumer provided a callback URL in "oauth_callback" (as described in Consumer Directs the User to the Service Provider (Section 6.2.1)), the Service Provider constructs an HTTP GET request URL, and redirects the User's web browser to that URL with the following parameters: oauth_token: The Request Token the User authorized or denied. The callback URL MAY include Consumer provided query parameters. The Service Provider MUST retain them unmodified and append the "oauth_token" parameter to the existing query. If no callback URL was provided, the Service Provider instructs the User to manually inform the Consumer that authorization has completed. 6.3. Obtaining an Access Token The Consumer exchanges the Request Token for an Access Token capable of accessing the Protected Resources. Obtaining an Access Token includes the following steps: 6.3.1. Consumer Requests an Access Token The Request Token and Token Secret MUST be exchanged for an Access Token and Token Secret. To request an Access Token, the Consumer makes an HTTP request to the Service Provider's Access Token URL. The Service Provider documentation specifies the HTTP method for this request, and HTTP POST is RECOMMENDED. The request MUST be signed per Signing Requests (Section 9), and contains the following parameters: Hammer-Lahav & Cook Expires April 3, 2009 [Page 12] Internet-Draft OAuth Authorization Protocol September 2008 oauth_consumer_key: The Consumer Key. oauth_token: The Request Token obtained previously. oauth_signature_method: The signature method the Consumer used to sign the request. oauth_signature: The signature as defined in Signing Requests (Section 9). oauth_timestamp: As defined in Nonce and Timestamp (Section 8). oauth_nonce: As defined in Nonce and Timestamp (Section 8). oauth_version: OPTIONAL. If present, value MUST be " 1.0 ". Service Providers MUST assume the protocol version to be "1.0" if this parameter is not present. Service Providers' response to non-"1.0" value is left undefined. No additional Service Provider specific parameters are allowed when requesting an Access Token to ensure all Token related information is present prior to seeking User approval. 6.3.2. Service Provider Grants an Access Token The Service Provider MUST ensure that: o The request signature has been successfully verified. o The Request Token has never been exchanged for an Access Token. o The Request Token matches the Consumer Key. If successful, the Service Provider generates an Access Token and Token Secret and returns them in the HTTP response body as defined in Service Provider Response Parameters (Section 5.2). The Access Token and Token Secret are stored by the Consumer and used when signing Protected Resources requests. The response contains the following parameters: oauth_token: The Access Token. oauth_token_secret: The Token Secret. Additional parameters: Any additional parameters, as defined by the Service Provider. If the request fails verification or is rejected for other reasons, Hammer-Lahav & Cook Expires April 3, 2009 [Page 13] Internet-Draft OAuth Authorization Protocol September 2008 the Service Provider SHOULD respond with the appropriate response code as defined in HTTP Response Codes (Section 10). The Service Provider MAY include some further details about why the request was rejected in the HTTP response body as defined in Service Provider Response Parameters (Section 5.2). 7. Accessing Protected Resources After successfully receiving the Access Token and Token Secret, the Consumer is able to access the Protected Resources on behalf of the User. The request MUST be signed per Signing Requests (Section 9), and contains the following parameters: oauth_consumer_key: The Consumer Key. oauth_token: The Access Token. oauth_signature_method: The signature method the Consumer used to sign the request. oauth_signature: The signature as defined in Signing Requests (Section 9). oauth_timestamp: As defined in Nonce and Timestamp (Section 8). oauth_nonce: As defined in Nonce and Timestamp (Section 8). oauth_version: OPTIONAL. If present, value MUST be "1.0". Service Providers MUST assume the protocol version to be "1.0" if this parameter is not present. Service Providers' response to non-"1.0" value is left undefined. Additional parameters: Any additional parameters, as defined by the Service Provider. 8. Nonce and Timestamp Unless otherwise specified by the Service Provider, the timestamp is expressed in the number of seconds since January 1, 1970 00:00:00 GMT. The timestamp value MUST be a positive integer and MUST be equal or greater than the timestamp used in previous requests. The Consumer SHALL then generate a Nonce value that is unique for all requests with that timestamp, Consumer Key, and Token combination. A nonce is a random string, uniquely generated for each request. The nonce allows the Service Provider to verify that a request has never Hammer-Lahav & Cook Expires April 3, 2009 [Page 14] Internet-Draft OAuth Authorization Protocol September 2008 been made before and helps prevent replay attacks when requests are made over a non-secure channel (such as HTTP). 9. Signing Requests All Token requests and Protected Resources requests MUST be signed by the Consumer and verified by the Service Provider. The purpose of signing requests is to prevent unauthorized parties from using the Consumer Key and Tokens when making Token requests or Protected Resources requests. The signature process encodes the Consumer Secret and Token Secret into a verifiable value which is included with the request. OAuth does not mandate a particular signature method, as each implementation can have its own unique requirements. The protocol defines three signature methods: "HMAC-SHA1", "RSA-SHA1", and "PLAINTEXT", but Service Providers are free to implement and document their own methods. Recommending any particular method is beyond the scope of this specification. The Consumer declares a signature method in the "oauth_signature_method" parameter, generates a signature, and stores it in the "oauth_signature" parameter. The Service Provider verifies the signature as specified in each method. When verifying a Consumer signature, the Service Provider SHOULD check the request nonce to ensure it has not been used in a previous Consumer request. The signature process MUST NOT change the request parameter names or values, with the exception of the "oauth_signature" parameter. 9.1. Signature Base String The Signature Base String is a consistent reproducible concatenation of the request elements into a single string. The string is used as an input in hashing or signing algorithms. The "HMAC-SHA1" signature method provides both a standard and an example of using the Signature Base String with a signing algorithm to generate signatures. 9.1.1. Parameter Encoding All parameter names and values MUST be encoded prior to constructing the Signature Base String. The encoding process uses the parameters in their original decoded form. It is essential that parameters are encoded in a certain way and need to be processed without any prior encoding. Text names and values are first encoded as UTF-8 octets per Hammer-Lahav & Cook Expires April 3, 2009 [Page 15] Internet-Draft OAuth Authorization Protocol September 2008 [RFC3629]. All parameter names and values are then escaped using the [RFC3986] percent-encoding (%XX) mechanism as follows: o Characters not in the unreserved character set ([RFC3986] section 2.3) MUST be encoded. o Characters in the unreserved character set MUST NOT be encoded. o Hexadecimal characters in encodings MUST be upper case. unreserved = ALPHA, DIGIT, '-', '.', '_', '~' 9.1.2. Normalize Request Parameters The request parameters are collected, sorted and concatenated into a normalized string: o Parameters in the OAuth HTTP Authorization header (Section 5.3.1) excluding the "realm" parameter. o Parameters in the HTTP POST request body (with a "content-type" of "application/x-www-form-urlencoded"). o Added to the URLs in the query part (as defined by [RFC3986] section 3). The "oauth_signature" parameter MUST be excluded. The parameters are normalized into a single string as follows: 1. Parameters are sorted by name, using lexicographical byte value ordering. If two or more parameters share the same name, they are sorted by their value. For example: a=1, c=hi%20there, f=25, f=50, f=a, z=p, z=t 2. Parameters are concatenated in their sorted order into a single string. For each parameter, the name is separated from the corresponding value by an '=' character (ASCII code 61), even if the value is empty. Each name-value pair is separated by an '&' character (ASCII code 38). For example: a=1&c=hi%20there&f=25&f=50&f=a&z=p&z=t Hammer-Lahav & Cook Expires April 3, 2009 [Page 16] Internet-Draft OAuth Authorization Protocol September 2008 9.1.3. Construct Request URL The Signature Base String includes the request absolute URL, tying the signature to a specific endpoint. The URL used in the Signature Base String MUST include the scheme, authority, and path, and MUST exclude the query and fragment as defined by [RFC3986] section 3. If the absolute request URL is not available to the Service Provider (it is always available to the Consumer), it can be constructed by combining the scheme being used, the HTTP "Host" header, and the relative HTTP request URL. If the "Host" header is not available, the Service Provider SHOULD use the host name communicated to the Consumer in the documentation or other means. The Service Provider SHOULD document the form of URL used in the Signature Base String to avoid ambiguity due to URL normalization. Unless specified, URL scheme and authority MUST be lowercase and include the port number; "http" default port 80 and "https" default port 443 MUST be excluded. For example, the request: HTTP://Example.com:80/resource?id=123 Is included in the Signature Base String as: http://example.com/resource 9.1.4. Concatenate Request Elements The following items MUST be concatenated in order into a single string. Each item is encoded (Section 9.1.1) and separated by an '&' character (ASCII code 38), even if empty. 1. The HTTP request method used to send the request. Value MUST be uppercase, for example: "HEAD", " GET ", "POST", etc. 2. The request URL from Section 9.1.3. 3. The normalized request parameters string from Section 9.1.2. See Signature Base String example in Appendix A.5.1. 9.2. HMAC-SHA1 The "HMAC-SHA1" signature method uses the HMAC-SHA1 signature algorithm as defined in [RFC2104] where the Signature Base String is the "text" and the "key" is the concatenated values (each first Hammer-Lahav & Cook Expires April 3, 2009 [Page 17] Internet-Draft OAuth Authorization Protocol September 2008 encoded per Parameter Encoding (Section 9.1.1)) of the Consumer Secret and Token Secret, separated by an '&' character (ASCII code 38) even if empty. 9.2.1. Generating Signature "oauth_signature" is set to the calculated "digest" octet string, first base64-encoded per [RFC2045] section 6.8, then URL-encoded per Parameter Encoding (Section 9.1.1). 9.2.2. Verifying Signature The Service Provider verifies the request by generating a new request signature octet string, and comparing it to the signature provided by the Consumer, first URL-decoded per Parameter Encoding (Section 9.1.1), then base64-decoded per [RFC2045] section 6.8. The signature is generated using the request parameters as provided by the Consumer, and the Consumer Secret and Token Secret as stored by the Service Provider. 9.3. RSA-SHA1 The "RSA-SHA1" signature method uses the RSASSA-PKCS1-v1_5 signature algorithm as defined in [RFC3447] section 8.2 (more simply known as PKCS#1), using SHA-1 as the hash function for EMSA-PKCS1-v1_5. It is assumed that the Consumer has provided its RSA public key in a verified way to the Service Provider, in a manner which is beyond the scope of this specification. 9.3.1. Generating Signature The Signature Base String is signed using the Consumer's RSA private key per [RFC3447] section 8.2.1, where "K" is the Consumer's RSA private key, "M" the Signature Base String, and "S" is the result signature octet string: S = RSASSA-PKCS1-V1_5-SIGN (K, M) "oauth_signature" is set to "S", first base64-encoded per [RFC2045] section 6.8, then URL-encoded per Parameter Encoding (Section 9.1.1). 9.3.2. Verifying Signature The Service Provider verifies the signature per [RFC3447] section 8.2.2, where " (n, e) " is the Consumer's RSA public key, "M" is the Signature Base String, and "S" is the octet string representation of the "oauth_signature" value: Hammer-Lahav & Cook Expires April 3, 2009 [Page 18] Internet-Draft OAuth Authorization Protocol September 2008 RSASSA-PKCS1-V1_5-VERIFY ((n, e), M, S) 9.4. PLAINTEXT The " PLAINTEXT " method does not provide any security protection and SHOULD only be used over a secure channel such as HTTPS. It does not use the Signature Base String. 9.4.1. Generating Signature "oauth_signature" is set to the concatenated encoded values of the Consumer Secret and Token Secret, separated by a '&' character (ASCII code 38), even if either secret is empty. The result MUST be encoded again. These examples show the value of "oauth_signature" for Consumer Secret "djr9rjt0jd78jf88" and 3 different Token Secrets: jjd999tj88uiths3: "oauth_signature"="djr9rjt0jd78jf88%26jjd999tj88uiths3" jjd99$tj88uiths3: "oauth_signature"="djr9rjt0jd78jf88%26jjd99%2524tj88uiths3" Empty: "oauth_signature"="djr9rjt0jd78jf88%26" 9.4.2. Verifying Signature The Service Provider verifies the request by breaking the signature value into the Consumer Secret and Token Secret, and ensures they match the secrets stored locally. 10. HTTP Response Codes This section applies only to the Request Token and Access Token requests. In general, the Service Provider SHOULD use the response codes defined in [RFC2616] Section 10. When the Service Provider rejects a Consumer request, it SHOULD respond with HTTP 400 Bad Request or HTTP 401 Unauthorized. o HTTP 400 Bad Request * Unsupported parameter * Unsupported signature method Hammer-Lahav & Cook Expires April 3, 2009 [Page 19] Internet-Draft OAuth Authorization Protocol September 2008 * Missing required parameter * Duplicated OAuth Protocol Parameter o HTTP 401 Unauthorized * Invalid Consumer Key * Invalid / expired Token * Invalid signature * Invalid / used nonce 11. IANA Considerations This memo includes no request to IANA. 12. Security Considerations 12.1. Credentials and Token Exchange The OAuth specification does not describe any mechanism for protecting Tokens and secrets from eavesdroppers when they are transmitted from the Service Provider to the Consumer in Section 6.1.2 and Section 6.3.2. Service Providers should ensure that these transmissions are protected using transport-layer mechanisms such as TLS or SSL. 12.2. RSA-SHA1 Signature Method When used with "RSA-SHA1" signatures, the OAuth protocol does not use the Consumer Secret and Token Secret. This means the protocol relies completely on the secrecy of the Private Key used by the Consumer to sign requests. 12.3. PLAINTEXT Signature Method When used with "PLAINTEXT" signatures, the OAuth protocol makes no attempts to protect User credentials from eavesdroppers or man-in- the-middle attacks. The "PLAINTEXT" signature algorithm is only intended to be used in conjunction with a transport-layer security mechanism such as TLS or SSL which does provide such protection. If transport-layer protection is unavailable, the "PLAINTEXT" signature method should not be used. Hammer-Lahav & Cook Expires April 3, 2009 [Page 20] Internet-Draft OAuth Authorization Protocol September 2008 12.4. Confidentiality of Requests While OAuth provides a mechanism for verifying the integrity of requests, it provides no guarantee of request confidentiality. Unless further precautions are taken, eavesdroppers will have full access to request content. Service Providers should carefully consider the kinds of data likely to be sent as part of such requests, and should employ transport-layer security mechanisms to protect sensitive resources. 12.5. Spoofing by Counterfeit Servers OAuth makes no attempt to verify the authenticity of the Service Provider. A hostile party could take advantage of this by intercepting the Consumer's requests and returning misleading or otherwise incorrect responses. Service providers should consider such attacks when developing services based on OAuth, and should require transport-layer security for any requests where the authenticity of the Service Provider or of request responses is an issue. 12.6. Proxying and Caching of Authenticated Content The HTTP Authorization scheme (Section 5.3) is optional. However, [RFC2616] relies on the "Authorization" and "WWW-Authenticate" headers to distinguish authenticated content so that it can be protected. Proxies and caches, in particular, may fail to adequately protect requests not using these headers. For example, private authenticated content may be stored in (and thus retrievable from) publicly-accessible caches. Service Providers not using the HTTP Authorization scheme (Section 5.3) should take care to use other mechanisms, such as the "Cache-Control" header, to ensure that authenticated content is protected. 12.7. Plaintext Storage of Credentials The Consumer Secret and Token Secret function the same way passwords do in traditional authentication systems. In order to compute the signatures used in the non-"PLAINTEXT" methods, the Service Provider must have access to these secrets in plaintext form. This is in contrast, for example, to modern operating systems, which store only a one-way hash of user credentials. If an attacker were to gain access to these secrets - or worse, to the Service Provider's database of all such secrets - he or she would be able to perform any action on behalf of any User. Accordingly, it is critical that Service Providers protect these secrets from Hammer-Lahav & Cook Expires April 3, 2009 [Page 21] Internet-Draft OAuth Authorization Protocol September 2008 unauthorized access. 12.8. Secrecy of the Consumer Secret In many applications, the Consumer application will be under the control of potentially untrusted parties. For example, if the Consumer is a freely available desktop application, an attacker may be able to download a copy for analysis. In such cases, attackers will be able to recover the Consumer Secret used to authenticate the Consumer to the Service Provider. Accordingly, Service Providers should not use the Consumer Secret alone to verify the identity of the Consumer. Where possible, other factors such as IP address should be used as well. 12.9. Phishing Attacks Wide deployment of OAuth and similar protocols may cause Users to become inured to the practice of being redirected to websites where they are asked to enter their passwords. If Users are not careful to verify the authenticity of these websites before entering their credentials, it will be possible for attackers to exploit this practice to steal Users' passwords. Service Providers should attempt to educate Users about the risks phishing attacks pose, and should provide mechanisms that make it easy for Users to confirm the authenticity of their sites. 12.10. Scoping of Access Requests By itself, OAuth does not provide any method for scoping the access rights granted to a Consumer. A Consumer either has access to Protected Resources or it doesn't. Many applications will, however, require greater granularity of access rights. For example, Service Providers may wish to make it possible to grant access to some Protected Resources but not others, or to grant only limited access (such as read-only access) to those Protected Resources. When implementing OAuth, Service Providers should consider the types of access Users may wish to grant Consumers, and should provide mechanisms to do so. Service Providers should also take care to ensure that Users understand the access they are granting, as well as any risks that may be involved. 12.11. Entropy of Secrets Unless a transport-layer security protocol is used, eavesdroppers will have full access to OAuth requests and signatures, and will thus Hammer-Lahav & Cook Expires April 3, 2009 [Page 22] Internet-Draft OAuth Authorization Protocol September 2008 be able to mount offline brute-force attacks to recover the Consumer's credentials used. Service Providers should be careful to assign Token Secrets and Consumer Secrets which are long enough - and random enough - to resist such attacks for at least the length of time that the secrets are valid. For example, if Token Secrets are valid for two weeks, Service Providers should ensure that it is not possible to mount a brute force attack that recovers the Token Secret in less than two weeks. Of course, Service Providers are urged to err on the side of caution, and use the longest secrets reasonable. It is equally important that the pseudo-random number generator (PRNG) used to generate these secrets be of sufficiently high quality. Many PRNG implementations generate number sequences that may appear to be random, but which nevertheless exhibit patterns or other weaknesses which make cryptanalysis or brute force attacks easier. Implementors should be careful to use cryptographically secure PRNGs to avoid these problems. 12.12. Denial of Service / Resource Exhaustion Attacks The OAuth protocol has a number of features which may make resource exhaustion attacks against Service Providers possible. For example, if a Service Provider includes a nontrivial amount of entropy in Token Secrets as recommended above, then an attacker may be able to exhaust the Service Provider's entropy pool very quickly by repeatedly obtaining Request Tokens from the Service Provider. Similarly, OAuth requires Service Providers to track used nonces. If an attacker is able to use many nonces quickly, the resources required to track them may exhaust available capacity. And again, OAuth can require Service Providers to perform potentially expensive computations in order to verify the signature on incoming requests. An attacker may exploit this to perform a denial of service attack by sending a large number of invalid requests to the Service Provider. Resource Exhaustion attacks are by no means specific to OAuth. However, OAuth implementors should be careful to consider the additional avenues of attack that OAuth exposes, and design their implementations accordingly. For example, entropy starvation typically results in either a complete denial of service while the system waits for new entropy or else in weak (easily guessable) secrets. When implementing OAuth, Service Providers should consider which of these presents a more serious risk for their application and design accordingly. Hammer-Lahav & Cook Expires April 3, 2009 [Page 23] Internet-Draft OAuth Authorization Protocol September 2008 12.13. Cryptographic Attacks SHA-1, the hash algorithm used in "HMAC-SHA1" signatures, has been shown [SHA1-CHARACTERISTICS] to have a number of cryptographic weaknesses that significantly reduce its resistance to collision attacks. Practically speaking, these weaknesses are difficult to exploit, and by themselves do not pose a significant risk to users of OAuth. They may, however, make more efficient attacks possible, and NIST has announced [SHA-COMMENTS] that it will phase out use of SHA-1 by 2010. Service Providers should take this into account when considering whether SHA-1 provides an adequate level of security for their applications. 12.14. Signature Base String Compatibility The Signature Base String has been designed to support the signature methods defined in this specification. When designing additional signature methods, the Signature Base String should be evaluated to ensure compatibility with the algorithms used. The Signature Base String cannot guarantee the order in which parameters are sent. If parameter ordering is important and affects the result of a request, the Signature Base String will not protect against request manipulation. Appendix A. Appendix A - Protocol Example In this example, the Service Provider photos.example.net is a photo sharing website, and the Consumer printer.example.com is a photo printing website. Jane, the User, would like printer.example.com to print the private photo " vacation.jpg " stored at photos.example.net. When Jane signs-into photos.example.net using her username and password, she can access the photo by going to the URL "http://photos.example.net/photo?file=vacation.jpg". Other Users cannot access that photo, and Jane does not want to share her username and password with printer.example.com. The requests in this example use the URL query method when sending parameters. This is done to simplify the example and should not be taken as an endorsement of one method over the others. Appendix A.1. Documentation and Registration The Service Provider documentation explains how to register for a Consumer Key and Consumer Secret, and declares the following URLs: Hammer-Lahav & Cook Expires April 3, 2009 [Page 24] Internet-Draft OAuth Authorization Protocol September 2008 Request Token URL: https://photos.example.net/request_token, using HTTP POST User Authorization URL: http://photos.example.net/authorize, using HTTP GET Access Token URL: https://photos.example.net/access_token, using HTTP POST Photo (Protected Resource) URL: http://photos.example.net/photo with required parameter "file" and optional parameter "size" The Service Provider declares support for the " HMAC-SHA1 " signature method for all requests, and "PLAINTEXT" only for secure (HTTPS) requests. The Consumer printer.example.com already established a Consumer Key and Consumer Secret with photos.example.net and advertizes its printing services for photos stored on photos.example.net. The Consumer registration is: Consumer Key: " dpf43f3p2l4k3l03 " Consumer Secret: "kd94hf93k423kf44" Appendix A.2. Obtaining a Request Token After Jane informs printer.example.com that she would like to print her vacation photo stored at photos.example.net, the printer website tries to access the photo and receives HTTP 401 Unauthorized indicating it is private. The Service Provider includes the following header with the response: WWW-Authenticate: OAuth realm="http://photos.example.net/" The Consumer sends the following HTTP POST request to the Service Provider: https://photos.example.net/request_token? oauth_consumer_key=dpf43f3p2l4k3l03&oauth_signature_method=PLAINTEXT& oauth_signature=kd94hf93k423kf44%26&oauth_timestamp=1191242090& oauth_nonce=hsu94j3884jdopsl&oauth_version=1.0 The Service Provider checks the signature and replies with an unauthorized Request Token in the body of the HTTP response: oauth_token=hh5s93j4hdidpola&oauth_token_secret=hdhd0244k9j7ao03 Hammer-Lahav & Cook Expires April 3, 2009 [Page 25] Internet-Draft OAuth Authorization Protocol September 2008 Appendix A.3. Requesting User Authorization The Consumer redirects Jane's browser to the Service Provider User Authorization URL to obtain Jane's approval for accessing her private photos. http://photos.example.net/authorize?oauth_token=hh5s93j4hdidpola& oauth_callback=http%3A%2F%2Fprinter.example.com%2Frequest_token_ready The Service Provider asks Jane to sign-in using her username and password and, if successful, asks her if she approves granting printer.example.com access to her private photos. If Jane approves the request, the Service Provider redirects her back to the Consumer's callback URL: http://printer.example.com/request_token_ready? oauth_token=hh5s93j4hdidpola Appendix A.4. Obtaining an Access Token Now that the Consumer knows Jane approved the Request Token, it asks the Service Provider to exchange it for an Access Token: https://photos.example.net/access_token? oauth_consumer_key=dpf43f3p2l4k3l03& oauth_token=hh5s93j4hdidpola&oauth_signature_method=PLAINTEXT& oauth_signature=kd94hf93k423kf44%26hdhd0244k9j7ao03& oauth_timestamp=1191242092& oauth_nonce=dji430splmx33448&oauth_version=1.0 The Service Provider checks the signature and replies with an Access Token in the body of the HTTP response: oauth_token=nnch734d00sl2jdk&oauth_token_secret=pfkkdhi9sl3r4s00 Appendix A.5. Accessing Protected Resources The Consumer is now ready to request the private photo. Since the photo URL is not secure (HTTP), it must use "HMAC-SHA1". Appendix A.5.1. Generating Signature Base String To generate the signature, it first needs to generate the Signature Base String. The request contains the following parameters ("oauth_signature" excluded) which are ordered and concatenated into a normalized string: Hammer-Lahav & Cook Expires April 3, 2009 [Page 26] Internet-Draft OAuth Authorization Protocol September 2008 oauth_consumer_key: "dpf43f3p2l4k3l03" oauth_token: "nnch734d00sl2jdk" oauth_signature_method: "HMAC-SHA1" oauth_timestamp: "1191242096" oauth_nonce: "kllo9940pd9333jh" oauth_version: "1.0" file: "vacation.jpg" size: "original" The following inputs are used to generate the Signature Base String: 1. "GET" 2. "http://photos.example.net/photos" 3. "file=vacation.jpg&oauth_consumer_key=dpf43f3p2l4k3l03&oauth_nonc e=kllo9940pd9333jh&oauth_signature_method=HMAC-SHA1&oauth_timesta mp=1191242096&oauth_token=nnch734d00sl2jdk&oauth_version=1.0&size =original" The Signature Base String is: GET&http%3A%2F%2Fphotos.example.net%2Fphotos&file%3Dvacation.jpg%26 oauth_consumer_key%3Ddpf43f3p2l4k3l03%26 oauth_nonce%3Dkllo9940pd9333jh%26 oauth_signature_method%3DHMAC-SHA1%26oauth_timestamp%3D1191242096%26 oauth_token%3Dnnch734d00sl2jdk%26oauth_version%3D1.0%26size%3Doriginal Appendix A.5.2. Calculating Signature Value HMAC-SHA1 produces the following "digest" value as a base64-encoded string (using the Signature Base String as "text" and " kd94hf93k423kf44&pfkkdhi9sl3r4s00 " as "key"): tR3+Ty81lMeYAr/Fid0kMTYa/WM= Appendix A.5.3. Requesting Protected Resource All together, the Consumer request for the photo is: Hammer-Lahav & Cook Expires April 3, 2009 [Page 27] Internet-Draft OAuth Authorization Protocol September 2008 http://photos.example.net/photos?file=vacation.jpg&size=original Authorization: OAuth realm="http://photos.example.net/", oauth_consumer_key="dpf43f3p2l4k3l03", oauth_token="nnch734d00sl2jdk", oauth_signature_method="HMAC-SHA1", oauth_signature="tR3%2BTy81lMeYAr%2FFid0kMTYa%2FWM%3D", oauth_timestamp="1191242096", oauth_nonce="kllo9940pd9333jh", oauth_version="1.0" And if using query parameters: http://photos.example.net/photos?file=vacation.jpg&size=original& oauth_consumer_key=dpf43f3p2l4k3l03&oauth_token=nnch734d00sl2jdk& oauth_signature_method=HMAC-SHA1& oauth_signature=tR3%2BTy81lMeYAr%2FFid0kMTYa%2FWM%3D& oauth_timestamp=1191242096& oauth_nonce=kllo9940pd9333jh&oauth_version=1.0 photos.example.net checks the signature and responds with the requested photo. Appendix B. Contributors The content and concepts within are a product of the OAuth community. It has been originally published as the [OAuth Core 1.0] community specification and was authored by: Mark Atwood (me@mark.atwood.name) Richard M. Conlan (zeveck@google.com) Blaine Cook (romeda@gmail.com) Leah Culver (leah@pownce.com) Kellan Elliott-McCrea (kellan@flickr.com) Larry Halff (larry@ma.gnolia.com) Eran Hammer-Lahav (eran@hueniverse.com) Ben Laurie (benl@google.com) Chris Messina (chris@citizenagency.com) Hammer-Lahav & Cook Expires April 3, 2009 [Page 28] Internet-Draft OAuth Authorization Protocol September 2008 John Panzer (jpanzer@acm.org) Sam Quigley (quigley@emerose.com) David Recordon (david@sixapart.com) Eran Sandler (eran@yedda.com) Jonathan Sergent (sergent@google.com) Todd Sieling (todd@ma.gnolia.com) Brian Slesinsky (brian-oauth@slesinsky.org) Andy Smith (andy@jaiku.com) 13. References 13.1. Normative References [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- Hashing for Message Authentication", RFC 2104, February 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., Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. [RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999. [RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC 3447, February 2003. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. Hammer-Lahav & Cook Expires April 3, 2009 [Page 29] Internet-Draft OAuth Authorization Protocol September 2008 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [W3C.REC-html40-19980424] Raggett, D., Jacobs, I., and A. Hors, "HTML 4.0 Specification", World Wide Web Consortium Recommendation REC-html40-19980424, April 1998, . 13.2. Informative References [OAuth Core 1.0] OAuth, OCW., "OAuth Core 1.0". [SHA-COMMENTS] National Institute of Standards and Technolog, NIST., "NIST Brief Comments on Recent Cryptanalytic Attacks on Secure Hashing Functions and the Continued Security Provided by SHA-1, August, 2004.". [SHA1-CHARACTERISTICS] De Canniere, C. and C. Rechberger, "Finding SHA-1 Characteristics: General Results and Applications". Authors' Addresses Eran Hammer-Lahav (editor) Email: eran@hueniverse.com URI: http://hueniverse.com Blaine Cook Email: romeda@gmail.com URI: http://romeda.org/ Hammer-Lahav & Cook Expires April 3, 2009 [Page 30] Internet-Draft OAuth Authorization Protocol September 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Hammer-Lahav & Cook Expires April 3, 2009 [Page 31]