The OAuth 2.0 Authorization Framework: Bearer Token Usage

https://tools.ietf.org/html/rfc6750

1.2. Terminology

   Bearer Token
      A security token with the property that any party in possession of
      the token (a "bearer") can use the token in any way that any other
      party in possession of it can.  Using a bearer token does not
      require a bearer to prove possession of cryptographic key material
      (proof-of-possession).

   All other terms are as defined in "The OAuth 2.0 Authorization
   Framework" [RFC6749].

1.3. Overview

   OAuth provides a method for clients to access a protected resource on
   behalf of a resource owner.  In the general case, before a client can
   access a protected resource, it must first obtain an authorization
   grant from the resource owner and then exchange the authorization
   grant for an access token.  The access token represents the grant's
   scope, duration, and other attributes granted by the authorization
   grant.  The client accesses the protected resource by presenting the
   access token to the resource server.  In some cases, a client can
   directly present its own credentials to an authorization server to
   obtain an access token without having to first obtain an
   authorization grant from a resource owner.

   The access token provides an abstraction, replacing different
   authorization constructs (e.g., username and password, assertion) for
   a single token understood by the resource server.  This abstraction
   enables issuing access tokens valid for a short time period, as well
   as removing the resource server's need to understand a wide range of
   authentication schemes.

     +--------+                               +---------------+
     |        |--(A)- Authorization Request ->|   Resource    |
     |        |                               |     Owner     |
     |        |<-(B)-- Authorization Grant ---|               |
     |        |                               +---------------+
     |        |
     |        |                               +---------------+
     |        |--(C)-- Authorization Grant -->| Authorization |
     | Client |                               |     Server    |
     |        |<-(D)----- Access Token -------|               |
     |        |                               +---------------+
     |        |
     |        |                               +---------------+
     |        |--(E)----- Access Token ------>|    Resource   |
     |        |                               |     Server    |
     |        |<-(F)--- Protected Resource ---|               |
     +--------+                               +---------------+

                     Figure 1: Abstract Protocol Flow

   The abstract OAuth 2.0 flow illustrated in Figure 1 describes the
   interaction between the client, resource owner, authorization server,
   and resource server (described in [RFC6749]).  The following two
   steps are specified within this document:

   (E)  The client requests the protected resource from the resource
        server and authenticates by presenting the access token.

   (F)  The resource server validates the access token, and if valid,
        serves the request.

   This document also imposes semantic requirements upon the access
   token returned in step (D).