Post from another form!

Hello,

CAS have integrated on our system and web applications is being included. There 
is a question mark for us in this step. I hope I'll explain to problem.

Trouble;
- There is a form which must be filled with text(memo box) in this case for 
authenticated or non-authenticaed users. 
- It is require to "login form" and one or more memo box must be same form. If 
a user haven't authenticated by CAS, how could be authenticate with a memo and 
login boxes?

Question;
Is there anyway to resolve this case or could it possible to fetch CAS login 
screen and then post?

thanks.