I can't make service routing work when base_url contains a path, ie BASE=https://example.com/satosa. (I'm trying with an OIDC frontend and SAML2 backend.)

The problem is that both backends register their endpoints with the base path (ie. satosa/samlbackend/acs/post), but routing.py expects the backend in the first element of context.path.split("/") (routing.py:160). In the example above, the selected backend will be "satosa", which is an invalid backend name.

It doesn't help that ModuleRouter doesn't know the base path, so it can not trim the base path from context.path.