Trying to bridge a username and pass so forum part of site would not need add login

[a.lai20]

I have been trying to find this thread for some time now and decided to post this up myself. Heres the problem, I am trying to remove the username and password because I have a site which requires people to log in in the home page which is not the forum. Once they log in, there is a tab for "forums". After clicking that tab, users are asked to choose a certain category which leads to opening of the forums.Also each category users choose is a different forum. The forum page isnt a new page by itself it just fills in the rest of the page which means the url does not change while u are clicking links on the forum. So the question is, is it possible to use the same username and password users use to login at the beginning of the site without having to login again at the forum section? Or in the account settings i can create a nickname for all the forums?

Ps. is there also any way to have the url change when something in the forum is changed with the setup I have.

Thank you.