I know its violates the Same origin policy, and that is why it is not possible through simple ajax request. I could use JSONP. But using JSONP for login doesn’t sound secure ( no post only get ).
So is there a more secure way of implementing login into https through ajax ?
Not only does it violate the same origin policy, but since the page you are calling from is insecure it has the potential to be interfered with and leak all the data you are trying to keep secure.
Use HTTPS for the entire process.
Better yet, keep using HTTPS while people are logged in, otherwise you will have the Firesheep problem.