This post generated from a question at StackOverflow; the question raised was, to how to redirect users in SharePoint using custom HttpHandler, when you do not have access to the server - or - have no permission to access the server/configuration.
HttpHandlers are used by IIS to "handle" different document types, for instance you have separate .asmx handle, .aspx handler, .ascx handler, etc.
Workaround 1: Look into SPUtility.Redirect
You can use the SPUtility.Redirect method whenever you want to direct the user to a different page. For example, you might create a landing page that determines the user's role membership, and based on that information you can redirect them to an appropriate page. Or, based on the contents of a query string issued by the user's browser, you might redirect them to a page that can process the query string, such as the Search Center results page.
Workaround 2: Disposable Windows SharePoint Services
Alternatively, you can look into Using Disposable Windows SharePoint Services Objects.
Workaround 3: Custom Handler in SharePoint
Create a custom HttpHandler in Windows SharePoint Services 3.0; whenever a user requests a url, your custom HttpHandler is going to process that. .Redirect() if you like the url, else otherwise.
But for your custom HttpHandler to work, it should be called first - so in your config file you will have to provide the value in path. Usually an extension is added here. But you can replace that with a * to work for all request. I believe that would work.