-spec from_changeset_fields(map()) ->
                               {json, integer(), map(), map()} | {asobi_error, asobi_error:code()}.

-spec provider_uid_taken([{atom(), binary()}]) -> boolean().

-spec registration_denied(binary()) -> {asobi_error, asobi_error:code()}.

-spec username_taken([{atom(), binary()}]) -> boolean().

-spec validation_failed(map()) -> {json, pos_integer(), map(), map()}.