def getCallBack(self, ps, post, action):
        '''post -- POST HTTP value
           action -- SOAP Action value
        '''
        node = self.getNode(post)
        if node is None:
            raise NoSuchFunction
        if node.authorize(None, post, action):
            return node.getOperation(ps, action)
        else:
            raise NotAuthorized, "Authorization failed for method %s" % action
post -- POST HTTP value
           action -- SOAP Action value