code: def get_federation_token(self, name, duration=None, policy=None):
          
          params = {'Name' : name}
          if duration:
              params['DurationSeconds'] = duration
          if policy:
              params['Policy'] = policy
          return self.get_object('GetFederationToken', params,
                                  FederationToken, verb='POST')
docs: :type name: str
          :param name: The name of the Federated user associated with
                       the credentials.
                       
          :type duration: int
          :param duration: The number of seconds the credentials should
                           remain valid.
  
          :type policy: str
          :param policy: A JSON policy to associate with these credentials.