errors.go
func ErrUnsupportedIdentity(id Identity) error {
	return ErrorResponse{
		Code:    http.StatusNotImplemented,
		Message: fmt.Sprintf("unsupported identity: %s/%s", id.Type, id.Format),
	}
}
func ErrUnsupportedIdentity(id Identity) error {
	return ErrorResponse{
		Code:    http.StatusNotImplemented,
		Message: fmt.Sprintf("unsupported identity: %s/%s", id.Type, id.Format),
	}
}
// ErrUnsupportedIdentity indicates the processor
// does not support the given identity type.