Custom login code
It would be nice if there was a way to add code to run when the user logs in, for example, we wish to log them in to another software too. This is currently impossible as the only thing available is an action hook, but that runs on the server-side and cannot generate a session (cookie) for the user.
The idea would be to log the user in to WHMCS and then run code in a given module/hook file. The code would run on the user's computer and this would allow other sessions to be generated.