Unprivileged logins

[Seirdy]

Currently, it's possible to authenticate with a password to get a short-lived token for full admin access. However, I imagine most CI users won't need full admin access; they may just wish to fetch all approved Webmentions.

It's possible to do this on the reverse-proxy level, e.g. by requiring basic auth or mtls to make certain requests. Perhaps this should be integrated into webmentiond directly, allowing us to get a token that's only valid for certain queries ("limit" and "status=approved" come to mind), or for read-only webmention access.

This isn't a terribly high-priority feature request; webmentiond works fine as-is.