Fix handling for non-root path URLs

[philippjfr]

Fixes #21

[MarcSkovMadsen]

It works for me on my Jupyterhub. Thx ❤️.

[MarcSkovMadsen]

One note is that on my Jupyterhub I need to add fastapi dev main.py --root-path /NAMESPACE/user/USERNAME/vscode/proxy/8000/ to get the /docs endpoint working. The Panel apps seems unaffected by this and continue to work.

[MarcSkovMadsen]

When this is deployed I will try also deploy fastapi Panel apps behind a reverse proxy on our kubernetes cluster. Will be awesome.

[philippjfr]

One note is that on my Jupyterhub I need to add fastapi dev main.py --root-path /NAMESPACE/user/USERNAME/vscode/proxy/8000/ to get the /docs endpoint working. The Panel apps seems unaffected by this and continue to work.

Right, maybe we can note that in our docs as well. This is required on the FastAPI side.