def addPolicyURI(self, policy_uri):
        """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
        """
        if policy_uri not in self.preferred_auth_policies:
            self.preferred_auth_policies.append(policy_uri)
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