Assembly: System.Web (in system.web.dll)
The FormsAuthenticationModule sets the current System.Web.HttpContext.User property to an IPrincipal object that represents the user identity for the current request when the authentication Mode is set to Forms in the authentication Element (ASP.NET Settings Schema) element of the application's configuration file.
The FormsAuthenticationModule exposes an Authenticate event that enables you to provide a custom IPrincipal object for the User property of the current HttpContext. The Authenticate event is accessed by specifying a subroutine named FormsAuthentication_OnAuthenticate in the Global.asax file for your ASP.NET application.
In IIS 7.0, using the WindowsAuthenticationModule with the FormsAuthenticationModule is not supported. For more information about compatibility issues in Integrated modes, see Upgrading ASP.NET Applications to IIS 7.0: Differences between IIS 7.0 Integrated Mode and Classic mode.