原地址：
http://msdn.microsoft.com/en-us/library/aa480476.aspx
IIS Authentication
ASP.NET authentication is a two-step process. First, Internet Information Services (IIS) authenticates the user and creates a Windows token to represent the user. IIS determines the authentication mode that it should use for a particular application by looking at IIS metabase settings. If IIS is configured to use anonymous authentication, a token for the IUSR_MACHINE account is generated and used to represent the anonymous user. IIS-then passes the token to ASP.NET.
Second, ASP.NET performs its own authentication. The authentication method used is specified by the mode attribute of the authentication element. The following authentication configuration specifies that ASP.NET uses the FormsAuthenticationModule class:
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<authentication mode="Forms" />
Note Because forms authentication does not rely on IIS authentication, you should configure anonymous access for your application in IIS if you intend to use forms authentication in your ASP.NET application.
ASP.NET Forms Authentication
ASP.NET forms authentication occurs after IIS authentication is completed. You can configure forms authentication with the forms element.
Forms Authentication Configuration
The default attribute values for forms authentication are shown in the following configuration-file fragment.
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<system.web>
<authentication mode="Forms">
<forms loginUrl="Login.aspx"
protection="All"
timeout="30"
name=".ASPXAUTH"
path="/"
requireSSL="false"
slidingExpiration="true"
defaultUrl="default.aspx"
cookieless="UseDeviceProfile"
enableCrossAppRedirects="false" />
</authentication>
</system.web>
The default attribute values are described below:
loginUrl points to your application's custom logon page. You should place
