Content Comparison

The OAuth 2.0 Specification describes four methods (flows) for obtaining access tokens

1. Authorization Code (3-leggedparty) http://tools.ietf.org/html/draft-ietf-oauth-v2-21#section-4.2
2. Implicit Grant  http://tools.ietf.org/html/draft-ietf-oauth-v2-21#section-4.1
3. Resource Owner Password Credentials  http://tools.ietf.org/html/draft-ietf-oauth-v2-21#section-4.3
4. Client Credentials (2-leggedparty)  http://tools.ietf.org/html/draft-ietf-oauth-v2-21#section-4.4

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Resource Owner Password Credentials (ROPC.)  Writing credential vault code to safely enter/store/manage user credentials for external servers is beyond the scope of the OAuth 2.0 client.  HOWEVER, if there was a credential vault in shindig a ROPC flow handler could be injected into the system.

Client Credentials can also could be handled rather simply and was implemented and test tested in this reference implementation.