Asp.net Form tag issue(Masterpage /Login-logout)

I am facing issue regarding the form tag

Actually I cant place form tag inside the master page coz i have some forms inside each pages. .(That needs to be serialize) And in the .aspx page we can only place only one form tag.

So i am in trouble to make a login/logout functionality as this can be done inside MasterPage only ..

Can someone suggest to go ahead...