Recommendations for authenticating Asp.net Ajax Requests using PageMethods

I am calling PageMethods for updating Gridview content in asp.net application [personal web app]. I would like to know a few recommendations with step 开发者_运维知识库by step actions to be taken by any developer in order to authenticate these PageMethod call's.

A sample code would be something like below :

function login(username,pass){
PageMethods(username,pass,success,failure,context,failure);} 

How can I validate the requests on server side? How do I make sure the request originates from whom it says to have come? I saw some similar posts but not the one with PageMethods. I had heard of nonce for ajax requests in wordpress. Does the same fit purpose here?

Well this was the question that solved this question too Securing Ajax Webmethod Requests