This clause allows requests to be redirected to a Handler based on the Handler's Identifier. This allows rapid selection of a Handler from amongst many Handlers using a hash-based match, instead of relying on the normal linear search that is used to find <Handler> clauses. This can be useful in special cases where there are many Handlers, and where a PreHandlerHook is able to identify the correct Handler to use.

When <AuthBy HANDLER> runs, it uses the HandlerId to create the name of the desired Handler to use. The named Handler is found based on its Identifier, and the request is redirected to that Handler.