There are three ways of doing authentication and authorization in ASP.NET:-
Windows authentication: - In this
methodology ASP.NET web pages will
use local windows users and groups to
authenticate and authorize resources.
Forms Authentication: - This is a
cookie based authentication where
username and password are stored on
client machines as cookie files or
they are sent through URL for every
request. Form-based authentication
presents the user with an HTML-based
Web page that prompts the user for
Passport authentication :- Passport
authentication is based on the
passport website provided by the
Microsoft .So when user logins with
credentials it will be reached to the
passport website ( i.e.
hotmail,devhood,windows live etc)
where authentication will happen. If
Authentication is successful it will
return a token to your website.