Find out if someone is logged in gmail, yahoo and facebook

Question

I am working on a web application where I have to tell user that he is logged in gmail or yahoo or facebook account. I think this can be done using cookies.
How to find out it?
what is the cookie name of these accounts, so that I can check their presence

Answer 1

Gmail can be tested by linking to a public image in your own google account. Facebook can be tested by loading your own profile, as a script. Both of these links will succeed if the person is logged into the respective service and fail if they are not. Afraid I don't know specific details for Yahoo but I imagine a similar technique would work.

A good article on this is located here, I believe the techniques both still work:

https://grepular.com/Abusing_HTTP_Status_Codes_to_Expose_Private_Information