Inconsistent use of base_url throughout the code

[mrvanes]

I tried to map SATOSA to a URI'd path behind a reverse proxy and didn't succeed. Looking through the code there are many mixes of the use of BASE (self.base_url) that defeat using it properly.

1. metadata (generation) uses it
2. register_endpoints of saml front and backend modules don't use it, but oidc frontend does
3. discovery return_url doesn't use it
4. saml2 backend ACS doesn't

This is where I stopped debugging and fixing the code.

All the above problems can be overcome seperately by wisely choosing a combination of reverse proxy conf (include base path in backend request or not) and SATOSA conf (with or without base path), but never together as as working system. It's a classical waterbed.

This issue is here only to address the problem, because we decided to go vhost based reverse proxy to keep the project going.

To clarify what I mean with base path URI'd SATOSA:
reverse proxy address: https:///satosa/
backend server: http://localhost:8080/ or http://localhost:8080/satosa