About login into sql server via asp.net

I want to design a form with C# that will able me to log in to my sql server with my sql login name and password.This should be the entry point, which is like the "SqlWebAdmin", Where i login first then have a view of databases that i have permission. The problem first is how to login into the sql server via ASP .net without knowing prior which database is mine?Any help plz?Most apps put their connect information in web.config, and read it out at run time.