Changed grant_type=AUTHORIZATION_CODE for grant_type=authorization_code

What does this MR do?

Changed grant_type=AUTHORIZATION_CODE for grant_type=authorization_code

Why was this MR needed?

Using the example when provided the parameter grant_type=AUTHORIZATION_CODE the server returns a error:

{"error":"unsupported_grant_type","error_description":"The authorization grant type is not supported by the authorization server."}