RFC 6749, "The OAuth 2.0 Authorization Framework", October 2012

Note: This RFC has been updated by RFC 8252, RFC 8996

Errata ID: 4745
Status: Reported
Type: Technical
Publication Format(s) : TEXT
Reported By: Clark Downum
Date Reported: 2016-07-20

Section 5.2 says:

error
         REQUIRED.  A single ASCII [USASCII] error code from the
         following:

         invalid_request
               The request is missing a required parameter, includes an
               unsupported parameter value (other than grant type),
               repeats a parameter, includes multiple credentials,
               utilizes more than one mechanism for authenticating the
               client, or is otherwise malformed.

         invalid_client
               Client authentication failed (e.g., unknown client, no
               client authentication included, or unsupported
               authentication method).  The authorization server MAY
               return an HTTP 401 (Unauthorized) status code to indicate
               which HTTP authentication schemes are supported.  If the
               client attempted to authenticate via the "Authorization"
               request header field, the authorization server MUST
               respond with an HTTP 401 (Unauthorized) status code and
               include the "WWW-Authenticate" response header field
               matching the authentication scheme used by the client.

         invalid_grant
               The provided authorization grant (e.g., authorization
               code, resource owner credentials) or refresh token is
               invalid, expired, revoked, does not match the redirection
               URI used in the authorization request, or was issued to
               another client.

         unauthorized_client
               The authenticated client is not authorized to use this
               authorization grant type.

         unsupported_grant_type
               The authorization grant type is not supported by the
               authorization server.

         invalid_scope
               The requested scope is invalid, unknown, malformed, or
               exceeds the scope granted by the resource owner.

         Values for the "error" parameter MUST NOT include characters
         outside the set %x20-21 / %x23-5B / %x5D-7E.

It should say:

error
         REQUIRED.  A single ASCII [USASCII] error code from the
         following:

         invalid_request
               The request is missing a required parameter, includes an
               unsupported parameter value (other than grant type),
               repeats a parameter, includes multiple credentials,
               utilizes more than one mechanism for authenticating the
               client, or is otherwise malformed.

         invalid_client
               Client authentication failed (e.g., unknown client, no
               client authentication included, or unsupported
               authentication method).  The authorization server MAY
               return an HTTP 401 (Unauthorized) status code to indicate
               which HTTP authentication schemes are supported.  If the
               client attempted to authenticate via the "Authorization"
               request header field, the authorization server MUST
               respond with an HTTP 401 (Unauthorized) status code and
               include the "WWW-Authenticate" response header field
               matching the authentication scheme used by the client.

         invalid_grant
               The provided authorization grant (e.g., authorization
               code, resource owner credentials) or refresh token is
               invalid, expired, revoked, does not match the redirection
               URI used in the authorization request, or was issued to
               another client.

         unauthorized_client
               The authenticated client is not authorized to use this
               authorization grant type.

         unsupported_grant_type
               The authorization grant type is not supported by the
               authorization server.

         invalid_scope
               The requested scope is invalid, unknown, malformed, or
               exceeds the scope granted by the resource owner.

         server_error
               The authorization server encountered an unexpected
               condition that prevented it from fulfilling the request.
               (This error code is needed because a 500 Internal Server
               Error HTTP status code cannot be returned to the client
               via an HTTP redirect.)

         temporarily_unavailable
               The authorization server is currently unable to handle
               the request due to a temporary overloading or maintenance
               of the server.  (This error code is needed because a 503
               Service Unavailable HTTP status code cannot be returned
               to the client via an HTTP redirect.)

         Values for the "error" parameter MUST NOT include characters
         outside the set %x20-21 / %x23-5B / %x5D-7E.

Notes:

This is simply adding the server_error and temporarily_unavailable errors in other responses responses to the access token response for non-implicit grant types.

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