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rfc:rfc5849

Internet Engineering Task Force (IETF) E. Hammer-Lahav, Ed. Request for Comments: 5849 April 2010 Category: Informational ISSN: 2070-1721

                       The OAuth 1.0 Protocol

Abstract

 OAuth provides a method for clients to access server resources on
 behalf of a resource owner (such as a different client or an end-
 user).  It also provides a process for end-users to authorize third-
 party access to their server resources without sharing their
 credentials (typically, a username and password pair), using user-
 agent redirections.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Not all documents
 approved by the IESG are a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5849.

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Hammer-Lahav Informational [Page 1] RFC 5849 OAuth 1.0 April 2010

Table of Contents

 1. Introduction ....................................................3
    1.1. Terminology ................................................4
    1.2. Example ....................................................5
    1.3. Notational Conventions .....................................7
 2. Redirection-Based Authorization .................................8
    2.1. Temporary Credentials ......................................9
    2.2. Resource Owner Authorization ..............................10
    2.3. Token Credentials .........................................12
 3. Authenticated Requests .........................................14
    3.1. Making Requests ...........................................14
    3.2. Verifying Requests ........................................16
    3.3. Nonce and Timestamp .......................................17
    3.4. Signature .................................................18
         3.4.1. Signature Base String ..............................18
         3.4.2. HMAC-SHA1 ..........................................25
         3.4.3. RSA-SHA1 ...........................................25
         3.4.4. PLAINTEXT ..........................................26
    3.5. Parameter Transmission ....................................26
         3.5.1. Authorization Header ...............................27
         3.5.2. Form-Encoded Body ..................................28
         3.5.3. Request URI Query ..................................28
    3.6. Percent Encoding ..........................................29
 4. Security Considerations ........................................29
    4.1. RSA-SHA1 Signature Method .................................29
    4.2. Confidentiality of Requests ...............................30
    4.3. Spoofing by Counterfeit Servers ...........................30
    4.4. Proxying and Caching of Authenticated Content .............30
    4.5. Plaintext Storage of Credentials ..........................30
    4.6. Secrecy of the Client Credentials .........................31
    4.7. Phishing Attacks ..........................................31
    4.8. Scoping of Access Requests ................................31
    4.9. Entropy of Secrets ........................................32
    4.10. Denial-of-Service / Resource-Exhaustion Attacks ..........32
    4.11. SHA-1 Cryptographic Attacks ..............................33
    4.12. Signature Base String Limitations ........................33
    4.13. Cross-Site Request Forgery (CSRF) ........................33
    4.14. User Interface Redress ...................................34
    4.15. Automatic Processing of Repeat Authorizations ............34
 5. Acknowledgments ................................................35
 Appendix A.  Differences from the Community Edition ...............36
 6. References .....................................................37
    6.1. Normative References ......................................37
    6.2. Informative References ....................................38

Hammer-Lahav Informational [Page 2] RFC 5849 OAuth 1.0 April 2010

1. Introduction

 The OAuth protocol was originally created by a small community of web
 developers from a variety of websites and other Internet services who
 wanted to solve the common problem of enabling delegated access to
 protected resources.  The resulting OAuth protocol was stabilized at
 version 1.0 in October 2007, and revised in June 2009 (Revision A) as
 published at <http://oauth.net/core/1.0a>.
 This specification provides an informational documentation of OAuth
 Core 1.0 Revision A, addresses several errata reported since that
 time, and makes numerous editorial clarifications.  While this
 specification is not an item of the IETF's OAuth Working Group, which
 at the time of writing is working on an OAuth version that can be
 appropriate for publication on the standards track, it has been
 transferred to the IETF for change control by authors of the original
 work.
 In the traditional client-server authentication model, the client
 uses its credentials to access its resources hosted by the server.
 With the increasing use of distributed web services and cloud
 computing, third-party applications require access to these server-
 hosted resources.
 OAuth introduces a third role to the traditional client-server
 authentication model: the resource owner.  In the OAuth model, the
 client (which is not the resource owner, but is acting on its behalf)
 requests access to resources controlled by the resource owner, but
 hosted by the server.  In addition, OAuth allows the server to verify
 not only the resource owner authorization, but also the identity of
 the client making the request.
 OAuth provides a method for clients to access server resources on
 behalf of a resource owner (such as a different client or an end-
 user).  It also provides a process for end-users to authorize third-
 party access to their server resources without sharing their
 credentials (typically, a username and password pair), using user-
 agent redirections.
 For example, a web user (resource owner) can grant a printing service
 (client) access to her private photos stored at a photo sharing
 service (server), without sharing her username and password with the
 printing service.  Instead, she authenticates directly with the photo
 sharing service which issues the printing service delegation-specific
 credentials.

Hammer-Lahav Informational [Page 3] RFC 5849 OAuth 1.0 April 2010

 In order for the client to access resources, it first has to obtain
 permission from the resource owner.  This permission is expressed in
 the form of a token and matching shared-secret.  The purpose of the
 token is to make it unnecessary for the resource owner to share its
 credentials with the client.  Unlike the resource owner credentials,
 tokens can be issued with a restricted scope and limited lifetime,
 and revoked independently.
 This specification consists of two parts.  The first part defines a
 redirection-based user-agent process for end-users to authorize
 client access to their resources, by authenticating directly with the
 server and provisioning tokens to the client for use with the
 authentication method.  The second part defines a method for making
 authenticated HTTP [RFC2616] requests using two sets of credentials,
 one identifying the client making the request, and a second
 identifying the resource owner on whose behalf the request is being
 made.
 The use of OAuth with any transport protocol other than [RFC2616] is
 undefined.

1.1. Terminology

 client
       An HTTP client (per [RFC2616]) capable of making OAuth-
       authenticated requests (Section 3).
 server
       An HTTP server (per [RFC2616]) capable of accepting OAuth-
       authenticated requests (Section 3).
 protected resource
       An access-restricted resource that can be obtained from the
       server using an OAuth-authenticated request (Section 3).
 resource owner
       An entity capable of accessing and controlling protected
       resources by using credentials to authenticate with the server.
 credentials
       Credentials are a pair of a unique identifier and a matching
       shared secret.  OAuth defines three classes of credentials:
       client, temporary, and token, used to identify and authenticate
       the client making the request, the authorization request, and
       the access grant, respectively.

Hammer-Lahav Informational [Page 4] RFC 5849 OAuth 1.0 April 2010

 token
       A unique identifier issued by the server and used by the client
       to associate authenticated requests with the resource owner
       whose authorization is requested or has been obtained by the
       client.  Tokens have a matching shared-secret that is used by
       the client to establish its ownership of the token, and its
       authority to represent the resource owner.
 The original community specification used a somewhat different
 terminology that maps to this specifications as follows (original
 community terms provided on left):
 Consumer:  client
 Service Provider:  server
 User:  resource owner
 Consumer Key and Secret:  client credentials
 Request Token and Secret:  temporary credentials
 Access Token and Secret:  token credentials

1.2. Example

 Jane (resource owner) has recently uploaded some private vacation
 photos (protected resources) to her photo sharing site
 'photos.example.net' (server).  She would like to use the
 'printer.example.com' website (client) to print one of these photos.
 Typically, Jane signs into 'photos.example.net' using her username
 and password.
 However, Jane does not wish to share her username and password with
 the 'printer.example.com' website, which needs to access the photo in
 order to print it.  In order to provide its users with better
 service, 'printer.example.com' has signed up for a set of
 'photos.example.net' client credentials ahead of time:
 Client Identifier
       dpf43f3p2l4k3l03
 Client Shared-Secret:
       kd94hf93k423kf44
 The 'printer.example.com' website has also configured its application
 to use the protocol endpoints listed in the 'photos.example.net' API
 documentation, which use the "HMAC-SHA1" signature method:

Hammer-Lahav Informational [Page 5] RFC 5849 OAuth 1.0 April 2010

 Temporary Credential Request
       https://photos.example.net/initiate
 Resource Owner Authorization URI:
       https://photos.example.net/authorize
 Token Request URI:
       https://photos.example.net/token
 Before 'printer.example.com' can ask Jane to grant it access to the
 photos, it must first establish a set of temporary credentials with
 'photos.example.net' to identify the delegation request.  To do so,
 the client sends the following HTTPS [RFC2818] request to the server:
   POST /initiate HTTP/1.1
   Host: photos.example.net
   Authorization: OAuth realm="Photos",
      oauth_consumer_key="dpf43f3p2l4k3l03",
      oauth_signature_method="HMAC-SHA1",
      oauth_timestamp="137131200",
      oauth_nonce="wIjqoS",
      oauth_callback="http%3A%2F%2Fprinter.example.com%2Fready",
      oauth_signature="74KNZJeDHnMBp0EMJ9ZHt%2FXKycU%3D"
 The server validates the request and replies with a set of temporary
 credentials in the body of the HTTP response (line breaks are for
 display purposes only):
   HTTP/1.1 200 OK
   Content-Type: application/x-www-form-urlencoded
   oauth_token=hh5s93j4hdidpola&oauth_token_secret=hdhd0244k9j7ao03&
   oauth_callback_confirmed=true
 The client redirects Jane's user-agent to the server's Resource Owner
 Authorization endpoint to obtain Jane's approval for accessing her
 private photos:
   https://photos.example.net/authorize?oauth_token=hh5s93j4hdidpola
 The server requests Jane to sign in using her username and password
 and if successful, asks her to approve granting 'printer.example.com'
 access to her private photos.  Jane approves the request and her
 user-agent is redirected to the callback URI provided by the client
 in the previous request (line breaks are for display purposes only):
   http://printer.example.com/ready?
   oauth_token=hh5s93j4hdidpola&oauth_verifier=hfdp7dh39dks9884

Hammer-Lahav Informational [Page 6] RFC 5849 OAuth 1.0 April 2010

 The callback request informs the client that Jane completed the
 authorization process.  The client then requests a set of token
 credentials using its temporary credentials (over a secure Transport
 Layer Security (TLS) channel):
   POST /token HTTP/1.1
   Host: photos.example.net
   Authorization: OAuth realm="Photos",
      oauth_consumer_key="dpf43f3p2l4k3l03",
      oauth_token="hh5s93j4hdidpola",
      oauth_signature_method="HMAC-SHA1",
      oauth_timestamp="137131201",
      oauth_nonce="walatlh",
      oauth_verifier="hfdp7dh39dks9884",
      oauth_signature="gKgrFCywp7rO0OXSjdot%2FIHF7IU%3D"
 The server validates the request and replies with a set of token
 credentials in the body of the HTTP response:
   HTTP/1.1 200 OK
   Content-Type: application/x-www-form-urlencoded
   oauth_token=nnch734d00sl2jdk&oauth_token_secret=pfkkdhi9sl3r4s00
 With a set of token credentials, the client is now ready to request
 the private photo:
   GET /photos?file=vacation.jpg&size=original HTTP/1.1
   Host: photos.example.net
   Authorization: OAuth realm="Photos",
      oauth_consumer_key="dpf43f3p2l4k3l03",
      oauth_token="nnch734d00sl2jdk",
      oauth_signature_method="HMAC-SHA1",
      oauth_timestamp="137131202",
      oauth_nonce="chapoH",
      oauth_signature="MdpQcU8iPSUjWoN%2FUDMsK2sui9I%3D"
 The 'photos.example.net' server validates the request and responds
 with the requested photo. 'printer.example.com' is able to continue
 accessing Jane's private photos using the same set of token
 credentials for the duration of Jane's authorization, or until Jane
 revokes access.

1.3. Notational Conventions

 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].

Hammer-Lahav Informational [Page 7] RFC 5849 OAuth 1.0 April 2010

2. Redirection-Based Authorization

 OAuth uses tokens to represent the authorization granted to the
 client by the resource owner.  Typically, token credentials are
 issued by the server at the resource owner's request, after
 authenticating the resource owner's identity (usually using a
 username and password).
 There are many ways in which a server can facilitate the provisioning
 of token credentials.  This section defines one such way, using HTTP
 redirections and the resource owner's user-agent.  This redirection-
 based authorization method includes three steps:
 1.  The client obtains a set of temporary credentials from the server
     (in the form of an identifier and shared-secret).  The temporary
     credentials are used to identify the access request throughout
     the authorization process.
 2.  The resource owner authorizes the server to grant the client's
     access request (identified by the temporary credentials).
 3.  The client uses the temporary credentials to request a set of
     token credentials from the server, which will enable it to access
     the resource owner's protected resources.
 The server MUST revoke the temporary credentials after being used
 once to obtain the token credentials.  It is RECOMMENDED that the
 temporary credentials have a limited lifetime.  Servers SHOULD enable
 resource owners to revoke token credentials after they have been
 issued to clients.
 In order for the client to perform these steps, the server needs to
 advertise the URIs of the following three endpoints:
 Temporary Credential Request
       The endpoint used by the client to obtain a set of temporary
       credentials as described in Section 2.1.
 Resource Owner Authorization
       The endpoint to which the resource owner is redirected to grant
       authorization as described in Section 2.2.
 Token Request
       The endpoint used by the client to request a set of token
       credentials using the set of temporary credentials as described
       in Section 2.3.

Hammer-Lahav Informational [Page 8] RFC 5849 OAuth 1.0 April 2010

 The three URIs advertised by the server MAY include a query component
 as defined by [RFC3986], Section 3, but if present, the query MUST
 NOT contain any parameters beginning with the "oauth_" prefix, to
 avoid conflicts with the protocol parameters added to the URIs when
 used.
 The methods in which the server advertises and documents its three
 endpoints are beyond the scope of this specification.  Clients should
 avoid making assumptions about the size of tokens and other server-
 generated values, which are left undefined by this specification.  In
 addition, protocol parameters MAY include values that require
 encoding when transmitted.  Clients and servers should not make
 assumptions about the possible range of their values.

2.1. Temporary Credentials

 The client obtains a set of temporary credentials from the server by
 making an authenticated (Section 3) HTTP "POST" request to the
 Temporary Credential Request endpoint (unless the server advertises
 another HTTP request method for the client to use).  The client
 constructs a request URI by adding the following REQUIRED parameter
 to the request (in addition to the other protocol parameters, using
 the same parameter transmission method):
 oauth_callback:  An absolute URI back to which the server will
                  redirect the resource owner when the Resource Owner
                  Authorization step (Section 2.2) is completed.  If
                  the client is unable to receive callbacks or a
                  callback URI has been established via other means,
                  the parameter value MUST be set to "oob" (case
                  sensitive), to indicate an out-of-band
                  configuration.
 Servers MAY specify additional parameters.
 When making the request, the client authenticates using only the
 client credentials.  The client MAY omit the empty "oauth_token"
 protocol parameter from the request and MUST use the empty string as
 the token secret value.
 Since the request results in the transmission of plain text
 credentials in the HTTP response, the server MUST require the use of
 a transport-layer mechanisms such as TLS or Secure Socket Layer (SSL)
 (or a secure channel with equivalent protections).

Hammer-Lahav Informational [Page 9] RFC 5849 OAuth 1.0 April 2010

 For example, the client makes the following HTTPS request:
   POST /request_temp_credentials HTTP/1.1
   Host: server.example.com
   Authorization: OAuth realm="Example",
      oauth_consumer_key="jd83jd92dhsh93js",
      oauth_signature_method="PLAINTEXT",
      oauth_callback="http%3A%2F%2Fclient.example.net%2Fcb%3Fx%3D1",
      oauth_signature="ja893SD9%26"
 The server MUST verify (Section 3.2) the request and if valid,
 respond back to the client with a set of temporary credentials (in
 the form of an identifier and shared-secret).  The temporary
 credentials are included in the HTTP response body using the
 "application/x-www-form-urlencoded" content type as defined by
 [W3C.REC-html40-19980424] with a 200 status code (OK).
 The response contains the following REQUIRED parameters:
 oauth_token
       The temporary credentials identifier.
 oauth_token_secret
       The temporary credentials shared-secret.
 oauth_callback_confirmed
       MUST be present and set to "true".  The parameter is used to
       differentiate from previous versions of the protocol.
 Note that even though the parameter names include the term 'token',
 these credentials are not token credentials, but are used in the next
 two steps in a similar manner to token credentials.
 For example (line breaks are for display purposes only):
   HTTP/1.1 200 OK
   Content-Type: application/x-www-form-urlencoded
   oauth_token=hdk48Djdsa&oauth_token_secret=xyz4992k83j47x0b&
   oauth_callback_confirmed=true

2.2. Resource Owner Authorization

 Before the client requests a set of token credentials from the
 server, it MUST send the user to the server to authorize the request.
 The client constructs a request URI by adding the following REQUIRED
 query parameter to the Resource Owner Authorization endpoint URI:

Hammer-Lahav Informational [Page 10] RFC 5849 OAuth 1.0 April 2010

 oauth_token
       The temporary credentials identifier obtained in Section 2.1 in
       the "oauth_token" parameter.  Servers MAY declare this
       parameter as OPTIONAL, in which case they MUST provide a way
       for the resource owner to indicate the identifier through other
       means.
 Servers MAY specify additional parameters.
 The client directs the resource owner to the constructed URI using an
 HTTP redirection response, or by other means available to it via the
 resource owner's user-agent.  The request MUST use the HTTP "GET"
 method.
 For example, the client redirects the resource owner's user-agent to
 make the following HTTPS request:
   GET /authorize_access?oauth_token=hdk48Djdsa HTTP/1.1
   Host: server.example.com
 The way in which the server handles the authorization request,
 including whether it uses a secure channel such as TLS/SSL is beyond
 the scope of this specification.  However, the server MUST first
 verify the identity of the resource owner.
 When asking the resource owner to authorize the requested access, the
 server SHOULD present to the resource owner information about the
 client requesting access based on the association of the temporary
 credentials with the client identity.  When displaying any such
 information, the server SHOULD indicate if the information has been
 verified.
 After receiving an authorization decision from the resource owner,
 the server redirects the resource owner to the callback URI if one
 was provided in the "oauth_callback" parameter or by other means.
 To make sure that the resource owner granting access is the same
 resource owner returning back to the client to complete the process,
 the server MUST generate a verification code: an unguessable value
 passed to the client via the resource owner and REQUIRED to complete
 the process.  The server constructs the request URI by adding the
 following REQUIRED parameters to the callback URI query component:
 oauth_token
       The temporary credentials identifier received from the client.

Hammer-Lahav Informational [Page 11] RFC 5849 OAuth 1.0 April 2010

 oauth_verifier
       The verification code.
 If the callback URI already includes a query component, the server
 MUST append the OAuth parameters to the end of the existing query.
 For example, the server redirects the resource owner's user-agent to
 make the following HTTP request:
   GET /cb?x=1&oauth_token=hdk48Djdsa&oauth_verifier=473f82d3 HTTP/1.1
   Host: client.example.net
 If the client did not provide a callback URI, the server SHOULD
 display the value of the verification code, and instruct the resource
 owner to manually inform the client that authorization is completed.
 If the server knows a client to be running on a limited device, it
 SHOULD ensure that the verifier value is suitable for manual entry.

2.3. Token Credentials

 The client obtains a set of token credentials from the server by
 making an authenticated (Section 3) HTTP "POST" request to the Token
 Request endpoint (unless the server advertises another HTTP request
 method for the client to use).  The client constructs a request URI
 by adding the following REQUIRED parameter to the request (in
 addition to the other protocol parameters, using the same parameter
 transmission method):
 oauth_verifier
       The verification code received from the server in the previous
       step.
 When making the request, the client authenticates using the client
 credentials as well as the temporary credentials.  The temporary
 credentials are used as a substitute for token credentials in the
 authenticated request and transmitted using the "oauth_token"
 parameter.
 Since the request results in the transmission of plain text
 credentials in the HTTP response, the server MUST require the use of
 a transport-layer mechanism such as TLS or SSL (or a secure channel
 with equivalent protections).

Hammer-Lahav Informational [Page 12] RFC 5849 OAuth 1.0 April 2010

 For example, the client makes the following HTTPS request:
   POST /request_token HTTP/1.1
   Host: server.example.com
   Authorization: OAuth realm="Example",
      oauth_consumer_key="jd83jd92dhsh93js",
      oauth_token="hdk48Djdsa",
      oauth_signature_method="PLAINTEXT",
      oauth_verifier="473f82d3",
      oauth_signature="ja893SD9%26xyz4992k83j47x0b"
 The server MUST verify (Section 3.2) the validity of the request,
 ensure that the resource owner has authorized the provisioning of
 token credentials to the client, and ensure that the temporary
 credentials have not expired or been used before.  The server MUST
 also verify the verification code received from the client.  If the
 request is valid and authorized, the token credentials are included
 in the HTTP response body using the
 "application/x-www-form-urlencoded" content type as defined by
 [W3C.REC-html40-19980424] with a 200 status code (OK).
 The response contains the following REQUIRED parameters:
 oauth_token
       The token identifier.
 oauth_token_secret
       The token shared-secret.
 For example:
   HTTP/1.1 200 OK
   Content-Type: application/x-www-form-urlencoded
   oauth_token=j49ddk933skd9dks&oauth_token_secret=ll399dj47dskfjdk
 The server must retain the scope, duration, and other attributes
 approved by the resource owner, and enforce these restrictions when
 receiving a client request made with the token credentials issued.
 Once the client receives and stores the token credentials, it can
 proceed to access protected resources on behalf of the resource owner
 by making authenticated requests (Section 3) using the client
 credentials together with the token credentials received.

Hammer-Lahav Informational [Page 13] RFC 5849 OAuth 1.0 April 2010

3. Authenticated Requests

 The HTTP authentication methods defined by [RFC2617] enable clients
 to make authenticated HTTP requests.  Clients using these methods
 gain access to protected resources by using their credentials
 (typically, a username and password pair), which allow the server to
 verify their authenticity.  Using these methods for delegation
 requires the client to assume the role of the resource owner.
 OAuth provides a method designed to include two sets of credentials
 with each request, one to identify the client, and another to
 identify the resource owner.  Before a client can make authenticated
 requests on behalf of the resource owner, it must obtain a token
 authorized by the resource owner.  Section 2 provides one such method
 through which the client can obtain a token authorized by the
 resource owner.
 The client credentials take the form of a unique identifier and an
 associated shared-secret or RSA key pair.  Prior to making
 authenticated requests, the client establishes a set of credentials
 with the server.  The process and requirements for provisioning these
 are outside the scope of this specification.  Implementers are urged
 to consider the security ramifications of using client credentials,
 some of which are described in Section 4.6.
 Making authenticated requests requires prior knowledge of the
 server's configuration.  OAuth includes multiple methods for
 transmitting protocol parameters with requests (Section 3.5), as well
 as multiple methods for the client to prove its rightful ownership of
 the credentials used (Section 3.4).  The way in which clients
 discover the required configuration is outside the scope of this
 specification.

3.1. Making Requests

 An authenticated request includes several protocol parameters.  Each
 parameter name begins with the "oauth_" prefix, and the parameter
 names and values are case sensitive.  Clients make authenticated
 requests by calculating the values of a set of protocol parameters
 and adding them to the HTTP request as follows:
 1.  The client assigns value to each of these REQUIRED (unless
     specified otherwise) protocol parameters:

Hammer-Lahav Informational [Page 14] RFC 5849 OAuth 1.0 April 2010

     oauth_consumer_key
       The identifier portion of the client credentials (equivalent to
       a username).  The parameter name reflects a deprecated term
       (Consumer Key) used in previous revisions of the specification,
       and has been retained to maintain backward compatibility.
     oauth_token
       The token value used to associate the request with the resource
       owner.  If the request is not associated with a resource owner
       (no token available), clients MAY omit the parameter.
     oauth_signature_method
       The name of the signature method used by the client to sign the
       request, as defined in Section 3.4.
     oauth_timestamp
       The timestamp value as defined in Section 3.3.  The parameter
       MAY be omitted when using the "PLAINTEXT" signature method.
     oauth_nonce
       The nonce value as defined in Section 3.3.  The parameter MAY
       be omitted when using the "PLAINTEXT" signature method.
     oauth_version
       OPTIONAL.  If present, MUST be set to "1.0".  Provides the
       version of the authentication process as defined in this
       specification.
 2.  The protocol parameters are added to the request using one of the
     transmission methods listed in Section 3.5.  Each parameter MUST
     NOT appear more than once per request.
 3.  The client calculates and assigns the value of the
     "oauth_signature" parameter as described in Section 3.4 and adds
     the parameter to the request using the same method as in the
     previous step.
 4.  The client sends the authenticated HTTP request to the server.
 For example, to make the following HTTP request authenticated (the
 "c2&a3=2+q" string in the following examples is used to illustrate
 the impact of a form-encoded entity-body):
   POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b HTTP/1.1
   Host: example.com
   Content-Type: application/x-www-form-urlencoded
   c2&a3=2+q

Hammer-Lahav Informational [Page 15] RFC 5849 OAuth 1.0 April 2010

 The client assigns values to the following protocol parameters using
 its client credentials, token credentials, the current timestamp, a
 uniquely generated nonce, and indicates that it will use the
 "HMAC-SHA1" signature method:
   oauth_consumer_key:     9djdj82h48djs9d2
   oauth_token:            kkk9d7dh3k39sjv7
   oauth_signature_method: HMAC-SHA1
   oauth_timestamp:        137131201
   oauth_nonce:            7d8f3e4a
 The client adds the protocol parameters to the request using the
 OAuth HTTP "Authorization" header field:
   Authorization: OAuth realm="Example",
                  oauth_consumer_key="9djdj82h48djs9d2",
                  oauth_token="kkk9d7dh3k39sjv7",
                  oauth_signature_method="HMAC-SHA1",
                  oauth_timestamp="137131201",
                  oauth_nonce="7d8f3e4a"
 Then, it calculates the value of the "oauth_signature" parameter
 (using client secret "j49sk3j29djd" and token secret "dh893hdasih9"),
 adds it to the request, and sends the HTTP request to the server:
   POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b HTTP/1.1
   Host: example.com
   Content-Type: application/x-www-form-urlencoded
   Authorization: OAuth realm="Example",
                  oauth_consumer_key="9djdj82h48djs9d2",
                  oauth_token="kkk9d7dh3k39sjv7",
                  oauth_signature_method="HMAC-SHA1",
                  oauth_timestamp="137131201",
                  oauth_nonce="7d8f3e4a",
                  oauth_signature="bYT5CMsGcbgUdFHObYMEfcx6bsw%3D"
   c2&a3=2+q

3.2. Verifying Requests

 Servers receiving an authenticated request MUST validate it by:
 o  Recalculating the request signature independently as described in
    Section 3.4 and comparing it to the value received from the client
    via the "oauth_signature" parameter.

Hammer-Lahav Informational [Page 16] RFC 5849 OAuth 1.0 April 2010

 o  If using the "HMAC-SHA1" or "RSA-SHA1" signature methods, ensuring
    that the combination of nonce/timestamp/token (if present)
    received from the client has not been used before in a previous
    request (the server MAY reject requests with stale timestamps as
    described in Section 3.3).
 o  If a token is present, verifying the scope and status of the
    client authorization as represented by the token (the server MAY
    choose to restrict token usage to the client to which it was
    issued).
 o  If the "oauth_version" parameter is present, ensuring its value is
    "1.0".
 If the request fails verification, the server SHOULD respond with the
 appropriate HTTP response status code.  The server MAY include
 further details about why the request was rejected in the response
 body.
 The server SHOULD return a 400 (Bad Request) status code when
 receiving a request with unsupported parameters, an unsupported
 signature method, missing parameters, or duplicated protocol
 parameters.  The server SHOULD return a 401 (Unauthorized) status
 code when receiving a request with invalid client credentials, an
 invalid or expired token, an invalid signature, or an invalid or used
 nonce.

3.3. Nonce and Timestamp

 The timestamp value MUST be a positive integer.  Unless otherwise
 specified by the server's documentation, the timestamp is expressed
 in the number of seconds since January 1, 1970 00:00:00 GMT.
 A nonce is a random string, uniquely generated by the client to allow
 the server to verify that a request has never been made before and
 helps prevent replay attacks when requests are made over a non-secure
 channel.  The nonce value MUST be unique across all requests with the
 same timestamp, client credentials, and token combinations.
 To avoid the need to retain an infinite number of nonce values for
 future checks, servers MAY choose to restrict the time period after
 which a request with an old timestamp is rejected.  Note that this
 restriction implies a level of synchronization between the client's
 and server's clocks.  Servers applying such a restriction MAY provide
 a way for the client to sync with the server's clock; alternatively,
 both systems could synchronize with a trusted time service.  Details
 of clock synchronization strategies are beyond the scope of this
 specification.

Hammer-Lahav Informational [Page 17] RFC 5849 OAuth 1.0 April 2010

3.4. Signature

 OAuth-authenticated requests can have two sets of credentials: those
 passed via the "oauth_consumer_key" parameter and those in the
 "oauth_token" parameter.  In order for the server to verify the
 authenticity of the request and prevent unauthorized access, the
 client needs to prove that it is the rightful owner of the
 credentials.  This is accomplished using the shared-secret (or RSA
 key) part of each set of credentials.
 OAuth provides three methods for the client to prove its rightful
 ownership of the credentials: "HMAC-SHA1", "RSA-SHA1", and
 "PLAINTEXT".  These methods are generally referred to as signature
 methods, even though "PLAINTEXT" does not involve a signature.  In
 addition, "RSA-SHA1" utilizes an RSA key instead of the shared-
 secrets associated with the client credentials.
 OAuth does not mandate a particular signature method, as each
 implementation can have its own unique requirements.  Servers are
 free to implement and document their own custom methods.
 Recommending any particular method is beyond the scope of this
 specification.  Implementers should review the Security
 Considerations section (Section 4) before deciding on which method to
 support.
 The client declares which signature method is used via the
 "oauth_signature_method" parameter.  It then generates a signature
 (or a string of an equivalent value) and includes it in the
 "oauth_signature" parameter.  The server verifies the signature as
 specified for each method.
 The signature process does not change the request or its parameters,
 with the exception of the "oauth_signature" parameter.

3.4.1. Signature Base String

 The signature base string is a consistent, reproducible concatenation
 of several of the HTTP request elements into a single string.  The
 string is used as an input to the "HMAC-SHA1" and "RSA-SHA1"
 signature methods.
 The signature base string includes the following components of the
 HTTP request:
 o  The HTTP request method (e.g., "GET", "POST", etc.).
 o  The authority as declared by the HTTP "Host" request header field.

Hammer-Lahav Informational [Page 18] RFC 5849 OAuth 1.0 April 2010

 o  The path and query components of the request resource URI.
 o  The protocol parameters excluding the "oauth_signature".
 o  Parameters included in the request entity-body if they comply with
    the strict restrictions defined in Section 3.4.1.3.
 The signature base string does not cover the entire HTTP request.
 Most notably, it does not include the entity-body in most requests,
 nor does it include most HTTP entity-headers.  It is important to
 note that the server cannot verify the authenticity of the excluded
 request components without using additional protections such as SSL/
 TLS or other methods.

3.4.1.1. String Construction

 The signature base string is constructed by concatenating together,
 in order, the following HTTP request elements:
 1.  The HTTP request method in uppercase.  For example: "HEAD",
     "GET", "POST", etc.  If the request uses a custom HTTP method, it
     MUST be encoded (Section 3.6).
 2.  An "&" character (ASCII code 38).
 3.  The base string URI from Section 3.4.1.2, after being encoded
     (Section 3.6).
 4.  An "&" character (ASCII code 38).
 5.  The request parameters as normalized in Section 3.4.1.3.2, after
     being encoded (Section 3.6).
 For example, the HTTP request:
   POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b HTTP/1.1
   Host: example.com
   Content-Type: application/x-www-form-urlencoded
   Authorization: OAuth realm="Example",
                  oauth_consumer_key="9djdj82h48djs9d2",
                  oauth_token="kkk9d7dh3k39sjv7",
                  oauth_signature_method="HMAC-SHA1",
                  oauth_timestamp="137131201",
                  oauth_nonce="7d8f3e4a",
                  oauth_signature="bYT5CMsGcbgUdFHObYMEfcx6bsw%3D"
   c2&a3=2+q

Hammer-Lahav Informational [Page 19] RFC 5849 OAuth 1.0 April 2010

 is represented by the following signature base string (line breaks
 are for display purposes only):
   POST&http%3A%2F%2Fexample.com%2Frequest&a2%3Dr%2520b%26a3%3D2%2520q
   %26a3%3Da%26b5%3D%253D%25253D%26c%2540%3D%26c2%3D%26oauth_consumer_
   key%3D9djdj82h48djs9d2%26oauth_nonce%3D7d8f3e4a%26oauth_signature_m
   ethod%3DHMAC-SHA1%26oauth_timestamp%3D137131201%26oauth_token%3Dkkk
   9d7dh3k39sjv7

3.4.1.2. Base String URI

 The scheme, authority, and path of the request resource URI [RFC3986]
 are included by constructing an "http" or "https" URI representing
 the request resource (without the query or fragment) as follows:
 1.  The scheme and host MUST be in lowercase.
 2.  The host and port values MUST match the content of the HTTP
     request "Host" header field.
 3.  The port MUST be included if it is not the default port for the
     scheme, and MUST be excluded if it is the default.  Specifically,
     the port MUST be excluded when making an HTTP request [RFC2616]
     to port 80 or when making an HTTPS request [RFC2818] to port 443.
     All other non-default port numbers MUST be included.
 For example, the HTTP request:
   GET /r%20v/X?id=123 HTTP/1.1
   Host: EXAMPLE.COM:80
 is represented by the base string URI: "http://example.com/r%20v/X".
 In another example, the HTTPS request:
   GET /?q=1 HTTP/1.1
   Host: www.example.net:8080
 is represented by the base string URI:
 "https://www.example.net:8080/".

3.4.1.3. Request Parameters

 In order to guarantee a consistent and reproducible representation of
 the request parameters, the parameters are collected and decoded to
 their original decoded form.  They are then sorted and encoded in a
 particular manner that is often different from their original
 encoding scheme, and concatenated into a single string.

Hammer-Lahav Informational [Page 20] RFC 5849 OAuth 1.0 April 2010

3.4.1.3.1. Parameter Sources

 The parameters from the following sources are collected into a single
 list of name/value pairs:
 o  The query component of the HTTP request URI as defined by
    [RFC3986], Section 3.4.  The query component is parsed into a list
    of name/value pairs by treating it as an
    "application/x-www-form-urlencoded" string, separating the names
    and values and decoding them as defined by
    [W3C.REC-html40-19980424], Section 17.13.4.
 o  The OAuth HTTP "Authorization" header field (Section 3.5.1) if
    present.  The header's content is parsed into a list of name/value
    pairs excluding the "realm" parameter if present.  The parameter
    values are decoded as defined by Section 3.5.1.
 o  The HTTP request entity-body, but only if all of the following
    conditions are met:
  • The entity-body is single-part.
  • The entity-body follows the encoding requirements of the

"application/x-www-form-urlencoded" content-type as defined by

       [W3C.REC-html40-19980424].
  • The HTTP request entity-header includes the "Content-Type"

header field set to "application/x-www-form-urlencoded".

    The entity-body is parsed into a list of decoded name/value pairs
    as described in [W3C.REC-html40-19980424], Section 17.13.4.
 The "oauth_signature" parameter MUST be excluded from the signature
 base string if present.  Parameters not explicitly included in the
 request MUST be excluded from the signature base string (e.g., the
 "oauth_version" parameter when omitted).

Hammer-Lahav Informational [Page 21] RFC 5849 OAuth 1.0 April 2010

 For example, the HTTP request:
     POST /request?b5=%3D%253D&a3=a&c%40=&a2=r%20b HTTP/1.1
     Host: example.com
     Content-Type: application/x-www-form-urlencoded
     Authorization: OAuth realm="Example",
                    oauth_consumer_key="9djdj82h48djs9d2",
                    oauth_token="kkk9d7dh3k39sjv7",
                    oauth_signature_method="HMAC-SHA1",
                    oauth_timestamp="137131201",
                    oauth_nonce="7d8f3e4a",
                    oauth_signature="djosJKDKJSD8743243%2Fjdk33klY%3D"
     c2&a3=2+q
 contains the following (fully decoded) parameters used in the
 signature base sting:
             +------------------------+------------------+
             |          Name          |       Value      |
             +------------------------+------------------+
             |           b5           |       =%3D       |
             |           a3           |         a        |
             |           c@           |                  |
             |           a2           |        r b       |
             |   oauth_consumer_key   | 9djdj82h48djs9d2 |
             |       oauth_token      | kkk9d7dh3k39sjv7 |
             | oauth_signature_method |     HMAC-SHA1    |
             |     oauth_timestamp    |     137131201    |
             |       oauth_nonce      |     7d8f3e4a     |
             |           c2           |                  |
             |           a3           |        2 q       |
             +------------------------+------------------+
 Note that the value of "b5" is "=%3D" and not "==".  Both "c@" and
 "c2" have empty values.  While the encoding rules specified in this
 specification for the purpose of constructing the signature base
 string exclude the use of a "+" character (ASCII code 43) to
 represent an encoded space character (ASCII code 32), this practice
 is widely used in "application/x-www-form-urlencoded" encoded values,
 and MUST be properly decoded, as demonstrated by one of the "a3"
 parameter instances (the "a3" parameter is used twice in this
 request).

Hammer-Lahav Informational [Page 22] RFC 5849 OAuth 1.0 April 2010

3.4.1.3.2. Parameters Normalization

 The parameters collected in Section 3.4.1.3 are normalized into a
 single string as follows:
 1.  First, the name and value of each parameter are encoded
     (Section 3.6).
 2.  The parameters are sorted by name, using ascending byte value
     ordering.  If two or more parameters share the same name, they
     are sorted by their value.
 3.  The name of each parameter is concatenated to its corresponding
     value using an "=" character (ASCII code 61) as a separator, even
     if the value is empty.
 4.  The sorted name/value pairs are concatenated together into a
     single string by using an "&" character (ASCII code 38) as
     separator.
 For example, the list of parameters from the previous section would
 be normalized as follows:
                               Encoded:
             +------------------------+------------------+
             |          Name          |       Value      |
             +------------------------+------------------+
             |           b5           |     %3D%253D     |
             |           a3           |         a        |
             |          c%40          |                  |
             |           a2           |       r%20b      |
             |   oauth_consumer_key   | 9djdj82h48djs9d2 |
             |       oauth_token      | kkk9d7dh3k39sjv7 |
             | oauth_signature_method |     HMAC-SHA1    |
             |     oauth_timestamp    |     137131201    |
             |       oauth_nonce      |     7d8f3e4a     |
             |           c2           |                  |
             |           a3           |       2%20q      |
             +------------------------+------------------+

Hammer-Lahav Informational [Page 23] RFC 5849 OAuth 1.0 April 2010

                                Sorted:
             +------------------------+------------------+
             |          Name          |       Value      |
             +------------------------+------------------+
             |           a2           |       r%20b      |
             |           a3           |       2%20q      |
             |           a3           |         a        |
             |           b5           |     %3D%253D     |
             |          c%40          |                  |
             |           c2           |                  |
             |   oauth_consumer_key   | 9djdj82h48djs9d2 |
             |       oauth_nonce      |     7d8f3e4a     |
             | oauth_signature_method |     HMAC-SHA1    |
             |     oauth_timestamp    |     137131201    |
             |       oauth_token      | kkk9d7dh3k39sjv7 |
             +------------------------+------------------+
                          Concatenated Pairs:
                +-------------------------------------+
                |              Name=Value             |
                +-------------------------------------+
                |               a2=r%20b              |
                |               a3=2%20q              |
                |                 a3=a                |
                |             b5=%3D%253D             |
                |                c%40=                |
                |                 c2=                 |
                | oauth_consumer_key=9djdj82h48djs9d2 |
                |         oauth_nonce=7d8f3e4a        |
                |   oauth_signature_method=HMAC-SHA1  |
                |      oauth_timestamp=137131201      |
                |     oauth_token=kkk9d7dh3k39sjv7    |
                +-------------------------------------+
 and concatenated together into a single string (line breaks are for
 display purposes only):
   a2=r%20b&a3=2%20q&a3=a&b5=%3D%253D&c%40=&c2=&oauth_consumer_key=9dj
   dj82h48djs9d2&oauth_nonce=7d8f3e4a&oauth_signature_method=HMAC-SHA1
   &oauth_timestamp=137131201&oauth_token=kkk9d7dh3k39sjv7

Hammer-Lahav Informational [Page 24] RFC 5849 OAuth 1.0 April 2010

3.4.2. HMAC-SHA1

 The "HMAC-SHA1" signature method uses the HMAC-SHA1 signature
 algorithm as defined in [RFC2104]:
   digest = HMAC-SHA1 (key, text)
 The HMAC-SHA1 function variables are used in following way:
 text    is set to the value of the signature base string from
         Section 3.4.1.1.
 key     is set to the concatenated values of:
         1.  The client shared-secret, after being encoded
             (Section 3.6).
         2.  An "&" character (ASCII code 38), which MUST be included
             even when either secret is empty.
         3.  The token shared-secret, after being encoded
             (Section 3.6).
 digest  is used to set the value of the "oauth_signature" protocol
         parameter, after the result octet string is base64-encoded
         per [RFC2045], Section 6.8.

3.4.3. RSA-SHA1

 The "RSA-SHA1" signature method uses the RSASSA-PKCS1-v1_5 signature
 algorithm as defined in [RFC3447], Section 8.2 (also known as
 PKCS#1), using SHA-1 as the hash function for EMSA-PKCS1-v1_5.  To
 use this method, the client MUST have established client credentials
 with the server that included its RSA public key (in a manner that is
 beyond the scope of this specification).
 The signature base string is signed using the client's RSA private
 key per [RFC3447], Section 8.2.1:
   S = RSASSA-PKCS1-V1_5-SIGN (K, M)
 Where:
 K     is set to the client's RSA private key,
 M     is set to the value of the signature base string from
       Section 3.4.1.1, and

Hammer-Lahav Informational [Page 25] RFC 5849 OAuth 1.0 April 2010

 S     is the result signature used to set the value of the
       "oauth_signature" protocol parameter, after the result octet
       string is base64-encoded per [RFC2045] section 6.8.
 The server verifies the signature per [RFC3447] section 8.2.2:
   RSASSA-PKCS1-V1_5-VERIFY ((n, e), M, S)
 Where:
 (n, e) is set to the client's RSA public key,
 M      is set to the value of the signature base string from
        Section 3.4.1.1, and
 S      is set to the octet string value of the "oauth_signature"
        protocol parameter received from the client.

3.4.4. PLAINTEXT

 The "PLAINTEXT" method does not employ a signature algorithm.  It
 MUST be used with a transport-layer mechanism such as TLS or SSL (or
 sent over a secure channel with equivalent protections).  It does not
 utilize the signature base string or the "oauth_timestamp" and
 "oauth_nonce" parameters.
 The "oauth_signature" protocol parameter is set to the concatenated
 value of:
 1.  The client shared-secret, after being encoded (Section 3.6).
 2.  An "&" character (ASCII code 38), which MUST be included even
     when either secret is empty.
 3.  The token shared-secret, after being encoded (Section 3.6).

3.5. Parameter Transmission

 When making an OAuth-authenticated request, protocol parameters as
 well as any other parameter using the "oauth_" prefix SHALL be
 included in the request using one and only one of the following
 locations, listed in order of decreasing preference:
 1.  The HTTP "Authorization" header field as described in
     Section 3.5.1.
 2.  The HTTP request entity-body as described in Section 3.5.2.

Hammer-Lahav Informational [Page 26] RFC 5849 OAuth 1.0 April 2010

 3.  The HTTP request URI query as described in Section 3.5.3.
 In addition to these three methods, future extensions MAY define
 other methods for including protocol parameters in the request.

3.5.1. Authorization Header

 Protocol parameters can be transmitted using the HTTP "Authorization"
 header field as defined by [RFC2617] with the auth-scheme name set to
 "OAuth" (case insensitive).
 For example:
   Authorization: OAuth realm="Example",
      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"
 Protocol parameters SHALL be included in the "Authorization" header
 field as follows:
 1.  Parameter names and values are encoded per Parameter Encoding
     (Section 3.6).
 2.  Each parameter's 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 "," character (ASCII code 44) and
     OPTIONAL linear whitespace per [RFC2617].
 4.  The OPTIONAL "realm" parameter MAY be added and interpreted per
     [RFC2617] section 1.2.
 Servers MAY indicate their support for the "OAuth" auth-scheme by
 returning the HTTP "WWW-Authenticate" response header field upon
 client requests for protected resources.  As per [RFC2617], such a
 response MAY include additional HTTP "WWW-Authenticate" header
 fields:
 For example:
   WWW-Authenticate: OAuth realm="http://server.example.com/"

Hammer-Lahav Informational [Page 27] RFC 5849 OAuth 1.0 April 2010

 The realm parameter defines a protection realm per [RFC2617], Section
 1.2.

3.5.2. Form-Encoded Body

 Protocol parameters can be transmitted in the HTTP request entity-
 body, but only if the following REQUIRED conditions are met:
 o  The entity-body is single-part.
 o  The entity-body follows the encoding requirements of the
    "application/x-www-form-urlencoded" content-type as defined by
    [W3C.REC-html40-19980424].
 o  The HTTP request entity-header includes the "Content-Type" header
    field set to "application/x-www-form-urlencoded".
 For example (line breaks are for display purposes only):
   oauth_consumer_key=0685bd9184jfhq22&oauth_token=ad180jjd733klr
   u7&oauth_signature_method=HMAC-SHA1&oauth_signature=wOJIO9A2W5
   mFwDgiDvZbTSMK%2FPY%3D&oauth_timestamp=137131200&oauth_nonce=4
   572616e48616d6d65724c61686176&oauth_version=1.0
 The entity-body MAY include other request-specific parameters, in
 which case, the protocol parameters SHOULD be appended following the
 request-specific parameters, properly separated by an "&" character
 (ASCII code 38).

3.5.3. Request URI Query

 Protocol parameters can be transmitted by being added to the HTTP
 request URI as a query parameter as defined by [RFC3986], Section 3.
 For example (line breaks are for display purposes only):
   GET /example/path?oauth_consumer_key=0685bd9184jfhq22&
   oauth_token=ad180jjd733klru7&oauth_signature_method=HM
   AC-SHA1&oauth_signature=wOJIO9A2W5mFwDgiDvZbTSMK%2FPY%
   3D&oauth_timestamp=137131200&oauth_nonce=4572616e48616
   d6d65724c61686176&oauth_version=1.0 HTTP/1.1
 The request URI MAY include other request-specific query parameters,
 in which case, the protocol parameters SHOULD be appended following
 the request-specific parameters, properly separated by an "&"
 character (ASCII code 38).

Hammer-Lahav Informational [Page 28] RFC 5849 OAuth 1.0 April 2010

3.6. Percent Encoding

 Existing percent-encoding methods do not guarantee a consistent
 construction of the signature base string.  The following percent-
 encoding method is not defined to replace the existing encoding
 methods defined by [RFC3986] and [W3C.REC-html40-19980424].  It is
 used only in the construction of the signature base string and the
 "Authorization" header field.
 This specification defines the following method for percent-encoding
 strings:
 1.  Text values are first encoded as UTF-8 octets per [RFC3629] if
     they are not already.  This does not include binary values that
     are not intended for human consumption.
 2.  The values are then escaped using the [RFC3986] percent-encoding
     (%XX) mechanism as follows:
  • Characters in the unreserved character set as defined by

[RFC3986], Section 2.3 (ALPHA, DIGIT, "-", ".", "_", "~") MUST

        NOT be encoded.
  • All other characters MUST be encoded.
  • The two hexadecimal characters used to represent encoded

characters MUST be uppercase.

 This method is different from the encoding scheme used by the
 "application/x-www-form-urlencoded" content-type (for example, it
 encodes space characters as "%20" and not using the "+" character).
 It MAY be different from the percent-encoding functions provided by
 web-development frameworks (e.g., encode different characters, use
 lowercase hexadecimal characters).

4. Security Considerations

 As stated in [RFC2617], the greatest sources of risks are usually
 found not in the core protocol itself but in policies and procedures
 surrounding its use.  Implementers are strongly encouraged to assess
 how this protocol addresses their security requirements.

4.1. RSA-SHA1 Signature Method

 Authenticated requests made with "RSA-SHA1" signatures do not use the
 token shared-secret, or any provisioned client shared-secret.  This
 means the request relies completely on the secrecy of the private key
 used by the client to sign requests.

Hammer-Lahav Informational [Page 29] RFC 5849 OAuth 1.0 April 2010

4.2. Confidentiality of Requests

 While this protocol 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.  Servers 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.

4.3. Spoofing by Counterfeit Servers

 This protocol makes no attempt to verify the authenticity of the
 server.  A hostile party could take advantage of this by intercepting
 the client's requests and returning misleading or otherwise incorrect
 responses.  Service providers should consider such attacks when
 developing services using this protocol, and should require
 transport-layer security for any requests where the authenticity of
 the server or of request responses is an issue.

4.4. Proxying and Caching of Authenticated Content

 The HTTP Authorization scheme (Section 3.5.1) is optional.  However,
 [RFC2616] relies on the "Authorization" and "WWW-Authenticate" header
 fields to distinguish authenticated content so that it can be
 protected.  Proxies and caches, in particular, may fail to adequately
 protect requests not using these header fields.
 For example, private authenticated content may be stored in (and thus
 retrievable from) publicly accessible caches.  Servers not using the
 HTTP "Authorization" header field should take care to use other
 mechanisms, such as the "Cache-Control" header field, to ensure that
 authenticated content is protected.

4.5. Plaintext Storage of Credentials

 The client shared-secret and token shared-secret function the same
 way passwords do in traditional authentication systems.  In order to
 compute the signatures used in methods other than "RSA-SHA1", the
 server 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 server's database of all such secrets -- he or she would be able
 to perform any action on behalf of any resource owner.  Accordingly,
 it is critical that servers protect these secrets from unauthorized
 access.

Hammer-Lahav Informational [Page 30] RFC 5849 OAuth 1.0 April 2010

4.6. Secrecy of the Client Credentials

 In many cases, the client application will be under the control of
 potentially untrusted parties.  For example, if the client is a
 desktop application with freely available source code or an
 executable binary, an attacker may be able to download a copy for
 analysis.  In such cases, attackers will be able to recover the
 client credentials.
 Accordingly, servers should not use the client credentials alone to
 verify the identity of the client.  Where possible, other factors
 such as IP address should be used as well.

4.7. Phishing Attacks

 Wide deployment of this and similar protocols may cause resource
 owners to become inured to the practice of being redirected to
 websites where they are asked to enter their passwords.  If resource
 owners 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 resource owners' passwords.
 Servers should attempt to educate resource owners about the risks
 phishing attacks pose, and should provide mechanisms that make it
 easy for resource owners to confirm the authenticity of their sites.
 Client developers should consider the security implications of how
 they interact with a user-agent (e.g., separate window, embedded),
 and the ability of the end-user to verify the authenticity of the
 server website.

4.8. Scoping of Access Requests

 By itself, this protocol does not provide any method for scoping the
 access rights granted to a client.  However, most applications do
 require greater granularity of access rights.  For example, servers
 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 this protocol, servers should consider the types of
 access resource owners may wish to grant clients, and should provide
 mechanisms to do so.  Servers should also take care to ensure that
 resource owners understand the access they are granting, as well as
 any risks that may be involved.

Hammer-Lahav Informational [Page 31] RFC 5849 OAuth 1.0 April 2010

4.9. Entropy of Secrets

 Unless a transport-layer security protocol is used, eavesdroppers
 will have full access to authenticated requests and signatures, and
 will thus be able to mount offline brute-force attacks to recover the
 credentials used.  Servers should be careful to assign shared-secrets
 that are long enough, and random enough, to resist such attacks for
 at least the length of time that the shared-secrets are valid.
 For example, if shared-secrets are valid for two weeks, servers
 should ensure that it is not possible to mount a brute force attack
 that recovers the shared-secret in less than two weeks.  Of course,
 servers 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 that nevertheless exhibit patterns or
 other weaknesses that make cryptanalysis or brute force attacks
 easier.  Implementers should be careful to use cryptographically
 secure PRNGs to avoid these problems.

4.10. Denial-of-Service / Resource-Exhaustion Attacks

 This specification includes a number of features that may make
 resource exhaustion attacks against servers possible.  For example,
 this protocol requires servers 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, this protocol can
 require servers 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 server.
 Resource Exhaustion attacks are by no means specific to this
 specification.  However, implementers should be careful to consider
 the additional avenues of attack that this protocol 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 this protocol, servers should
 consider which of these presents a more serious risk for their
 application and design accordingly.

Hammer-Lahav Informational [Page 32] RFC 5849 OAuth 1.0 April 2010

4.11. SHA-1 Cryptographic Attacks

 SHA-1, the hash algorithm used in "HMAC-SHA1" and "RSA-SHA1"
 signature methods, has been shown to have a number of cryptographic
 weaknesses that significantly reduce its resistance to collision
 attacks.  While these weaknesses do not seem to affect the use of
 SHA-1 with the Hash-based Message Authentication Code (HMAC) and
 should not affect the "HMAC-SHA1" signature method, it may affect the
 use of the "RSA-SHA1" signature method.  NIST has announced that it
 will phase out use of SHA-1 in digital signatures by 2010
 [NIST_SHA-1Comments].
 Practically speaking, these weaknesses are difficult to exploit, and
 by themselves do not pose a significant risk to users of this
 protocol.  They may, however, make more efficient attacks possible,
 and servers should take this into account when considering whether
 SHA-1 provides an adequate level of security for their applications.

4.12. Signature Base String Limitations

 The signature base string has been designed to support the signature
 methods defined in this specification.  Those designing additional
 signature methods, should evaluated the compatibility of the
 signature base string with their security requirements.
 Since the signature base string does not cover the entire HTTP
 request, such as most request entity-body, most entity-headers, and
 the order in which parameters are sent, servers should employ
 additional mechanisms to protect such elements.

4.13. Cross-Site Request Forgery (CSRF)

 Cross-Site Request Forgery (CSRF) is a web-based attack whereby HTTP
 requests are transmitted from a user that the website trusts or has
 authenticated.  CSRF attacks on authorization approvals can allow an
 attacker to obtain authorization to protected resources without the
 consent of the User.  Servers SHOULD strongly consider best practices
 in CSRF prevention at all the protocol authorization endpoints.
 CSRF attacks on OAuth callback URIs hosted by clients are also
 possible.  Clients should prevent CSRF attacks on OAuth callback URIs
 by verifying that the resource owner at the client site intended to
 complete the OAuth negotiation with the server.  The methods for
 preventing such CSRF attacks are beyond the scope of this
 specification.

Hammer-Lahav Informational [Page 33] RFC 5849 OAuth 1.0 April 2010

4.14. User Interface Redress

 Servers should protect the authorization process against user
 interface (UI) redress attacks (also known as "clickjacking").  As of
 the time of this writing, no complete defenses against UI redress are
 available.  Servers can mitigate the risk of UI redress attacks using
 the following techniques:
 o  JavaScript frame busting.
 o  JavaScript frame busting, and requiring that browsers have
    JavaScript enabled on the authorization page.
 o  Browser-specific anti-framing techniques.
 o  Requiring password reentry before issuing OAuth tokens.

4.15. Automatic Processing of Repeat Authorizations

 Servers may wish to automatically process authorization requests
 (Section 2.2) from clients that have been previously authorized by
 the resource owner.  When the resource owner is redirected to the
 server to grant access, the server detects that the resource owner
 has already granted access to that particular client.  Instead of
 prompting the resource owner for approval, the server automatically
 redirects the resource owner back to the client.
 If the client credentials are compromised, automatic processing
 creates additional security risks.  An attacker can use the stolen
 client credentials to redirect the resource owner to the server with
 an authorization request.  The server will then grant access to the
 resource owner's data without the resource owner's explicit approval,
 or even awareness of an attack.  If no automatic approval is
 implemented, an attacker must use social engineering to convince the
 resource owner to approve access.
 Servers can mitigate the risks associated with automatic processing
 by limiting the scope of token credentials obtained through automated
 approvals.  Tokens credentials obtained through explicit resource
 owner consent can remain unaffected.  Clients can mitigate the risks
 associated with automatic processing by protecting their client
 credentials.

Hammer-Lahav Informational [Page 34] RFC 5849 OAuth 1.0 April 2010

5. Acknowledgments

 This specification is directly based on the OAuth Core 1.0 Revision A
 community specification, which in turn was modeled after existing
 proprietary protocols and best practices that have been independently
 implemented by various companies.
 The community specification was edited by Eran Hammer-Lahav and
 authored by: Mark Atwood, Dirk Balfanz, Darren Bounds, Richard M.
 Conlan, Blaine Cook, Leah Culver, Breno de Medeiros, Brian Eaton,
 Kellan Elliott-McCrea, Larry Halff, Eran Hammer-Lahav, Ben Laurie,
 Chris Messina, John Panzer, Sam Quigley, David Recordon, Eran
 Sandler, Jonathan Sergent, Todd Sieling, Brian Slesinsky, and Andy
 Smith.
 The editor would like to thank the following individuals for their
 invaluable contribution to the publication of this edition of the
 protocol: Lisa Dusseault, Justin Hart, Avshalom Houri, Chris Messina,
 Mark Nottingham, Tim Polk, Peter Saint-Andre, Joseph Smarr, and Paul
 Walker.

Hammer-Lahav Informational [Page 35] RFC 5849 OAuth 1.0 April 2010

Appendix A. Differences from the Community Edition

 This specification includes the following changes made to the
 original community document [OAuthCore1.0_RevisionA] in order to
 correct mistakes and omissions identified since the document was
 originally published at <http://oauth.net>.
 o  Changed using TLS/SSL when sending or requesting plain text
    credentials from SHOULD to MUST.  This change affects any use of
    the "PLAINTEXT" signature method, as well as requesting temporary
    credentials (Section 2.1) and obtaining token credentials
    (Section 2.3).
 o  Adjusted nonce language to indicate it is unique per token/
    timestamp/client combination.
 o  Removed the requirement for timestamps to be equal to or greater
    than the timestamp used in the previous request.
 o  Changed the nonce and timestamp parameters to OPTIONAL when using
    the "PLAINTEXT" signature method.
 o  Extended signature base string coverage that includes
    "application/x-www-form-urlencoded" entity-body parameters when
    the HTTP method used is other than "POST" and URI query parameters
    when the HTTP method used is other than "GET".
 o  Incorporated corrections to the instructions in each signature
    method to encode the signature value before inserting it into the
    "oauth_signature" parameter, removing errors that would have
    caused double-encoded values.
 o  Allowed omitting the "oauth_token" parameter when empty.
 o  Permitted sending requests for temporary credentials with an empty
    "oauth_token" parameter.
 o  Removed the restrictions from defining additional "oauth_"
    parameters.

Hammer-Lahav Informational [Page 36] RFC 5849 OAuth 1.0 April 2010

6. References

6.1. 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.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
 [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.
 [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]
            Hors, A., Raggett, D., and I. Jacobs, "HTML 4.0
            Specification", World Wide Web Consortium
            Recommendation REC-html40-19980424, April 1998,
            <http://www.w3.org/TR/1998/REC-html40-19980424>.

Hammer-Lahav Informational [Page 37] RFC 5849 OAuth 1.0 April 2010

6.2. Informative References

 [NIST_SHA-1Comments]
            Burr, W., "NIST Comments on Cryptanalytic Attacks on
            SHA-1",
            <http://csrc.nist.gov/groups/ST/hash/statement.html>.
 [OAuthCore1.0_RevisionA]
            OAuth Community, "OAuth Core 1.0 Revision A",
            <http://oauth.net/core/1.0a>.

Author's Address

 Eran Hammer-Lahav (editor)
 EMail: eran@hueniverse.com
 URI:   http://hueniverse.com

Hammer-Lahav Informational [Page 38]

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