single sign on asp.net and apache

[pat3d2]

Hello. I have a website made in ASP.NET 2, with a login page. I'm not using the membership class. I'm checking in the active directory if my user exists. If I have found my user, a new page appear with different links. There is one on an Apache server. How can I do to not login again,on apache server ? What should I put in my web config file for authentication mode ? "forms or windows" ? How apache knows that I'm already connected ? Thanks in advance for your help. Pat3d