[FR] "secure" the OPML Route

[robertkleinschuster]

Is your feature request related to a problem? Please describe.
Currently the OPML url is always the same and is not protected by any auth. It exposes all the other rss feeds and does defeat the purpose of using the UUIDs.

Describe the solution you'd like
Setting a secret via env variable that is used as part of the route.

Describe alternatives you've considered
Generating a uuid and saving it in the settings and using that in the route.
Not exposing the OPML route with expose_feed_endpoints.

[robertkleinschuster]

sorry, I just realized that a bit late @kieraneglin