Authentication mechanisms in ASP.Net

ASP.Net Generally supports 3 types of authentication mechanisms.
1.Windows authentication
2.Form authentication
3.Passport authentication

Out of above 3 mechanisms, commonly used 2 methods are windows and form.

Enabling this mechanisms are simple.
Open your application's web.config file and add tag and specify the mode.
learn more about authentication mechanisms

Now in form authentication you may need to use your Activedirectory or DataBase for authentication.
2 ways to do that.

1. Writing your own code to query your database or Activedirectory.
(in this case if u want to change your DB or AD you need to edit your code and recompile.)

here is a method to change your DB or AD with out editing code.

2. This can be done using Membership in .net by
adding tag to your web.config file.
learn more about membership

here i have given you very top level view. You may face problems in implementation. Write to me if you need any help.