Onion service is auto-redirecting to clearnet

[micahflee]

Describe the bug
The onion service for https://tips.hushline.app/ is http://hyewn4dvbedq7ooe3oxrhpceljd7ncfyeyts2c7nwsjp34i46smbzwid.onion/, however it seems that if you load the site using the onion service hostname it auto-redirects to SERVER_NAME, which is tips.hushline.app.

To Reproduce
Steps to reproduce the behavior:

Open Tor Browser, load https://tips.hushline.app/, and click ".onion available". It loads the onion service, which redirects back to https://tips.hushline.app/.

Expected behavior
You should be able to use the onion service.

[brassy-endomorph]

I have this snipped in another project and it would obviously need modifying, but it could be set up to a single app like this. It's a few years old and from the Flask 2.x release series, so idk if there's a better way to do it.

class DomainDispatcher:
    def __init__(self, domains):
        self.domains = domains

    def __call__(self, environ, start_response):
        request_host = environ['HTTP_HOST']
        for (domain, app) in self.domains:
            if request_host.endswith(domain):
                return app(environ, start_response)

        # TODO instead of aborting 503, replace with call to simple app that renders a
        # simple page "service not available" static page.
        # nginx should redirect to this too when the service is down
        abort(503)


def create_app(config: Config = None) -> DomainDispatcher:
    if config is None:
        config = Config()

    domains = []
    for domain in config.domains:
        # make a copy so we can fiddle with some of the options for this sub-app
        domains.append((domain, make_app(copy.deepcopy(config), domain)))

    return DomainDispatcher(domains)


def make_app(config: Config, domain: str = None) -> Flask:
    # normal app.route, app.config, etc. stuff here

The disadvantage of this is I had some dangerous mangling of the Config in make_app where I was doing things like if domain.endswith(".onion"): ... and then tweaking things.

I actually think the best way to deploy this would be using two containers each with fully separate (but in some cases copy/pasted) configs because for example in #626 there almost certainly would be a difference in the proxy config for clearnet vs. Tor which would require a totally different Config (and/or set of env vars), and no tricky mangling within make_app would be able to account for this without being highly brittle and tied to our particular setup.