'Get the openid.return_to argument from this response.
This is useful for verifying that this request was initiated
by this consumer.
@returns: The return_to URL supplied to the server on the
initial request, or C{None} if the response did not contain
an C{openid.return_to} argument.
@returntype: str'

def getReturnTo(self):

    return self.getSigned(OPENID_NS, 'return_to')
