Authentication is the process of discovering and verifying the identity of a principal by examining the user's credentials and validating those credentials against some authority. The information obtained during authentication is directly usable by your code. That is, once the identity of the principal is discovered, you can use .NET Framework role-based security to determine whether to allow that principal to access your code.
A variety of authentication mechanisms are used today, many of which can be used with .NET Framework role-based security. Some of the most commonly used mechanisms are basic, digest, Passport, operating system (such as NTLM or Kerberos), or application-defined mechanisms.