'Create credentials that act as domain-wide delegation of authority.
Use the ``sub`` parameter as the subject to delegate on behalf of
that user.
For example::
>>> account_sub = \'foo@email.com\'
>>> delegate_creds = creds.create_delegated(account_sub)
Args:
sub: string, An email address that this service account will
act on behalf of (via domain-wide delegation).
Returns:
ServiceAccountCredentials, a copy of the current service account
updated to act on behalf of ``sub``.'

def create_delegated(self, sub):

    return self.create_with_claims({'sub': sub})
