Add access to Router in AuthHandlerFactory

**Is your feature request related to a problem? Please describe.**
When attempting to implement OAuth2 based security, with OOTB Vert.x functionalities, I've encountered a need to register custom routing when creating the handler.

**Describe the solution you'd like**
AuthHandlerFactory should have the possibility to register some custom routing, required for example for an OAuth2 callback.

**Describe alternatives you've considered**
It is possible to implement it as two different OpenAPI3 based endpoints, but it breaks the isolation between security logic and routing logic (business logic).

Start by locating AuthHandlerFactory and the Router integration points in the server project. Review how authentication handlers are created and how routing is currently registered, then verify that an OAuth2 callback can use custom routing without breaking the separation between security and business logic.

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