About the site to get a cookie problem under another site

Existing A, a (domain name is not the same) two sites, a website login, will save a cookie, then B site want to know which user a station login, that is, want to get this cookie value.

Is there any way to do this with curl? Or not through curl, by other means to get

Reply to discussion (solution)

A website to do an interface, B directly read the interface can not ... Get the client to do it?

A website to do an interface, B directly read the interface can not ... To get the client to do it? Trouble, can you tell me a little bit more?

Siteb.js

$.get (' sitea_api.php?salt= authentication key &time= current timestamp ', function () {      //Perform login operation});

sitea_api.php

if (MyCheck ($salt)) {//Check if key is correct    echo $uid;//output current User ID}

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