Support serving Outline from a subpath

Problem


Outline currently works well when served from the root of a domain, for example:



However, some self-hosted deployments need to serve Outline from a subpath, for example:



Today this is difficult because several client and server paths assume /, including API routes, static assets, OAuth/auth routes, realtime websocket routes, collaboration websocket routes, and the service worker scope.

Proposal


Would the core team be open to a BASE_PATH configuration option?

For example:

`env
URL=
BASE_PATH=/outline