'Add a authentication policy to this response
This method is intended to be used by the provider to add a
policy that the provider conformed to when authenticating the user.
@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'

def addPolicyURI(self, policy_uri):

    if (policy_uri not in self.auth_policies):
        self.auth_policies.append(policy_uri)
