title: Difference between client authentication and authorization grant in OAuth using JWT
body: <p>I have been reading <a href="https://datatracker.ietf.org/doc/html/draft-ietf-oauth-jwt-bearer-04" rel="nofollow noreferrer">this spec</a> for using JWT (JSON web tokens) with OAuth.</p>
  <p>In <a href="https://datatracker.ietf.org/doc/html/draft-ietf-oauth-jwt-bearer-04#section-2.1" rel="nofollow noreferrer">2.1</a> and <a href="https://datatracker.ietf.org/doc/html/draft-ietf-oauth-jwt-bearer-04#section-2.2" rel="nofollow noreferrer">2.2</a>, it says that JWTs can be used as Authorization Grants or Client Authentication.</p>
  <p>From my understanding, authentication is to identify something (this user is who he claims to be) and authorization is to check if a user is allowed to do what he requested.</p>
  <p>JWT as authorization grant makes sense, because the request is implicit identified by being signed. Most APIs that support this method uses JWT as an authorization grant. See <a href="http://help.salesforce.com/help/doc/en/remoteaccess_oauth_jwt_flow.htm" rel="nofollow noreferrer">salesforce</a> and <a href="https://developers.google.com/accounts/docs/OAuth2ServiceAccount" rel="nofollow noreferrer">google</a>.</p>
  <p>This is where it gets confusing for me. <strong>Why is it that there need for JWT Authentication as a separate thing?</strong> <em>Under what situations/use cases will there be a need for JWT Authentication?</em></p>