Is there no ext hook to access the post data from the login form?

I have a client that wants me to add a “remember my info” checkbox to the login form so that next time they come back it prefills their username. I told him that almost all modern browsers do this, but, well you know.

So, I need to add a checkbox to the login form and then access that post data to evaluate it and set a cookie if its checked, but I don’t see that I can access the login form post data in any of the existing hooks.

Ideas?