Subdirectory App Url

[notquitenothing]

Is your feature request related to a problem? Please describe:

There should be a way to host VoidAuth on a subpath (ex. https://example.com/voidauth) instead of a subdomain (ex. https://voidauth.example.com).

Describe the solution you'd like:

It should be possible to host on a subpath by configuring my reverse proxy correctly, and including the subpath in the APP_URL environment variable. There should also be at least a few examples in the docs for reverse proxy configuration.

Describe alternatives you've considered:

While I don't mind hosting VoidAuth as a subdomain, it should be possible to use a subpath too.

[notquitenothing]

The node-oidc-provider library I use for OIDC does use the HOST header for some interaction/resume logic, so that header cannot be overwritten. That means that the express app will need to be aware of the subdirectory when mounting all of the endpoints. I should be able to find it from the APP_URL environment variable