OAuth error codes

The following OAuth error codes are currently defined:

• not_implemented – request not implemented
• access_denied – access denied
• missing_signature – missing request signature header
• invalid_signature – invalid request signature
• invalid_parameters – invalid parameters
• invalid_client_secret – wrong API key
• token_refresh_error – error occurred while refreshing a token
• token_create_error – error occurred while creating a token
• invalid_device_code – invalid or expired device code
• invalid_client_id – invalid client id
• authorization_pending – authorization pending, keep polling
• invalid_response_type – invalid response type parameter
• invalid_key_type – invalid key type parameter
• invalid_endpoint – client not found in the database
• endpoint_not_authorized – endpoint is not authorized for token refresh operation