SERVER_NAME setting must match host exactly

[guruofgentoo]

Else all routes 404. Let's determine why that is - maybe something in request routing that matches requests to a specific flask app.

[guruofgentoo]

level12/keg-app-cookiecutter#49 is related.

[guruofgentoo]

https://github.com/pallets/flask/blob/192f4ae0b2a4e7d73c0b0472e53e33250175d786/src/flask/app.py#L1711

The setting gets passed down into werkzeug for matching. Werkzeug's default is to use the host name from the request itself if that parameter is not provided. Since Flask passes it in, though, Werkzeug is flagging requests as having the wrong subdomain, issuing a warning, and responding 404 to everything.

If we want to resolve this, the easiest method will be to put a custom url_map_class on the app, and patch bind/bind_to_environ to ignore the server name. That will imply, though, that we don't want this validation on requests.

TBH I don't remember the origin of this issue - not sure if it was something we wanted to change, or just to understand why it was happening. We should discuss before proceeding.