总的来说，有如下事件会依次触发。
BeginRequest
AuthenticateRequest
AuthorizeRequest
ResolveRequestCache
AcquireRequestState
PreRequestHandlerExecute
PostRequestHandlerExecute
ReleaseRequestState
UpdateRequestCache
EndRequest
此外，有三个不确定的顺序：
PreSendRequestHeaders
PreSendRequestContent
Error
那么，当我们注册了多个Module之后会怎么样呢？
举个例子：
如果你在web.config配置了两个HttpModule，分别是HttpModuleA，HttpModuleB
这个事件执行的顺序如下：
HttpModuleA->BeginRequest
HttpModuleB->BeginRequest
HttpModuleA->AuthenticateRequest
HttpModuleB->AuthenticateRequest
HttpModuleA->AuthorizeRequest
HttpModuleB->AuthorizeRequest
...以此类推
当然了，系统默认的那些Module总是在自定义Module之前执行
Framework中默认的Module（C:\windows\microsoft.net\Framework\v2.0.50727\CONFIG\web.config）
<httpModules>
<add name="OutputCache" type="System.Web.Caching.OutputCacheModule"/>
<add name="Session" type="System.Web.SessionState.SessionStateModule"/>
<add name="WindowsAuthentication" type="System.Web.Security.WindowsAuthenticationModule"/>
<add name="FormsAuthentication" type="System.Web.Security.FormsAuthenticationModule"/>
<add name="PassportAuthentication" type="System.Web.Security.PassportAuthenticationModule"/>
<add name="RoleManager" type="System.Web.Security.RoleManagerModule"/>
<add name="UrlAuthorization" type="System.Web.Security.UrlAuthorizationModule"/>
<add name="FileAuthorization" type="System.Web.Security.FileAuthorizationModule"/>
<add name="AnonymousIdentification" type="System.Web.Security.AnonymousIdentificationModule"/>
<add name="Profile" type="System.Web.Profile.ProfileModule"/>
<add name="ErrorHandlerModule" type="System.Web.Mobile.ErrorHandlerModule, System.Web.Mobile,
Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>
<add name="ServiceModel" type="System.ServiceModel.Activation.HttpModule, System.ServiceModel,
Version=3.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>
</httpModules>