how to check from JavaScript if loaded page has ASP.NET authentication cookie?

Question

It looks like JavaScript does not have access to authentication cookies ('ASP.NET_SessionId', '.ASPXFORMSAUTH')

in the http headers I can see cookies but document.cookie object does not have them.

Answer 1

You could create a WebMethod which uses the following code to return a true/false value:

[WebMethod]
public bool IsAuthenticated()
{
    return HttpRequest.IsAuthenticated;
}

Call this from javascript using jQuery or MSAJAX.

Answer 2

ASP.NET session cookies are HTTP-only by default (and rightfully so). If you need to find out if the user is authenticated in Javascript, putting a HiddenField on the page and setting its value to 0 or 1 based on your authentication token is a much better solution.