Authentik in a subfolder: Embedded outpost and /media folder do not work

[Ra72xx]

Describe the bug
I switched from using Authentik in the root folder to using authentik in a subfolder by setting
AUTHENTIK__WEB_PATH=/authentik/
This basically works, but it seems as if (at least) the folders

/media/
/outpost.goauthentik.io/

are now no longer reachable. None of the following paths works:

http://localhost:9000/media
http://localhost:9000/authentik/media
http://localhost:9000/outpost.goauthentik.io/ping
http://localhost:9000/authentik/outpost.goauthentik.io/ping
https://external.domain:port/media
https://external.domain:port/authentik/media
https://external.domain:port/outpost.goauthentik.io/ping
https://external.domain:port/authentik/outpost.goauthentik.io/ping

The external domain is proxied by Nginx, but as the un-proxied localhost connection also does not work for these paths, it does not seem to be a proxy problem.

This makes stuff like application icons, avatars and especially the embedded outpost unavailable, as requests produce an 404 error.

Other functionality, as far as I use it (web ui, LDAP outpost, oidc endpoints) seems to work.

To Reproduce
Enable Authentik in a subfolder as per documentation. The installation was in the root folder in the same domain (but with another port) before.

Expected behavior
After changing all path entries in the configuration, Authentik should work in a subfolder the same way as in the root folder.

Logs
Logs contain no hints concerning this error

Version and Deployment (please complete the following information):

• authentik version: 2025.2.4
• Deployment: Custom podman units for all Authentik components build like the Docker examples in the documentation.