When to use HTTP Modules versus Global.asax Files
One should use a module whenever one must create code that depends on application events, and when the following conditions are true:
One want to re-use the module in other applications.
You want to avoid putting complex code in the Global.asax file.
The module applies to all requests in the pipeline (IIS 7.0 Integrated mode only).
One should add code in the Global.asax file whenever