Sharing session between two different web browser

Question

I want to make a PHP web application in which on a single PC there can only be one authentication session at a time i.e. User A login using

Answer 1

You can accomplish this task (assuming your working with general users, who doesn't try to spoof User-Agents and other tricks) by using a signature algorithm which identifies a device. Your algorithm can have as many variables as you see fit.

For example REMOTE_ADDR, USER_AGENT. Other special variables can be obtain by executing a flash based code on the client side. As each request comes in you can compare it with existing keys that are authenticated and if you get a new session where all variables match except a Browser String you can safely assume its the same user using a different browser.

You must collect extra variables using a flash component for this to work. the variables available via $_SERVER is not sufficient. Because there could be users behind proxies and you do not want to identify them as false positive.