code: def addPolicyURI(self, policy_uri):
          
          if policy_uri not in self.preferred_auth_policies:
              self.preferred_auth_policies.append(policy_uri)
docs: Add an acceptable authentication policy URI to this request
  
          This method is intended to be used by the relying party to add
          acceptable authentication types to the request.
  
          @param policy_uri: The identifier for the preferred type of
              authentication.
          @see: http://openid.net/specs/openid-provider-authentication-policy-extension-1_0-01.html#auth_policies