Here are the event occurred in life cycle of HTTPApplication
1. BeginRequest. The request processing starts.
2. AuthenticateRequest. The request is authenticated. IIS 7 and ASP.NET authentication modules subscribe to this stage to perform authentication.
4. AuthorizeRequest. The request is authorized. IIS 7 and ASP.NET authorization modules check whether the authenticated user has access to the resource requested.
6. ResolveRequestCache. Cache modules check whether the response to this request exists in the cache, and return it instead of proceeding with the rest of the execution path. Both ASP.NET Output Cache and IIS 7 Output Cache features execute.
8. MapRequestHandler. This stage is internal in ASP.NET and is used to determine the request handler.
10. AcquireRequestState. The state necessary for the request execution is retrieved. ASP.NET Session State and Profile modules obtain their data.
12. PreExecuteRequestHandler. Any tasks before the execution of the handler are performed.
13. ExecuteRequestHandler. The request handler executes. ASPX pages, ASP pages, CGI programs, and static files are served.
15. ReleaseRequestState. The request state changes are saved, and the state is cleaned up here. ASP.NET Session State and Profile modules use this stage for cleanup.
17. UpdateRequestCache. The response is stored in the cache for future use. The ASP.NET Output Cache and IIS 7 Output Cache modules execute to save the response to their caches.
19. LogRequest. This stage logs the results of the request, and is guaranteed to execute even if errors occur.
21. EndRequest. This stage performs any final request cleanup, and is guaranteed to execute even if errors occur.
By using the familiar ASP.NET APIs, the ability to execute in the same stages as IIS 7 modules makes tasks that were only previously accessible in native ISAPI filters and extensions now possible in managed code.