You could try FormsAuthentication.RedirectFromLoginPage (http://msdn.microsoft.com/en-us/library/ka5ffkce.aspx), which sets the cookie (I believe,though you may have to manually set the cookie), and then redirect to the designated page to redirect from (specified in the configuration file for the  auth settings).  Essentially, after setting the cookie, you do have to do a redirect or postback after setting it, because it won't look like the application has enabled your authentication.

HTH.

ASP.NET membership/ automatically log existing user on
I try to compile Raspbian, [ http://hermess.no-ip.org/rpi/index.php ]
when I Prime kernel with the old config: make ARCH=arm CROSS_COMPILE=${CCPREFIX} oldconfig I get a lot lot of dialog messages, so is the file .config useless??? 
