def CheckValidCreds(self, request, context):
    """Returns true if valid credentials exist for the given data source and
    requesting user.
    Some data sources doesn't support service account, so we need to talk to
    them on behalf of the end user. This API just checks whether we have OAuth
    token for the particular user, which is a pre-requisite before user can
    create a transfer config.
    """
    context.set_code(grpc.StatusCode.UNIMPLEMENTED)
    context.set_details('Method not implemented!')
    raise NotImplementedError('Method not implemented!')