User-Agent header not set by `notify_push` nor `test_client`

[yds]

my logs are full of this error:

WARN [notify_push::connection] /build/source/src/connection.rs:99: Error while sending authentication request to nextcloud: Client error: 403 Forbidden

this is because NextCloud is deployed behind HAProxy with an anti-DDoS setting to block any connections without something/anything set in the User-Agent header:

http-request deny unless { req.hdr(user-agent) -m found }

here's a link to a Lighttpd recipe to enable the same anti-DDoS measures.

disabling these anti-DDoS measures to allow for notify_push requests to get through is not a wise choice -- the number of attacks attempts goes up noticeably.

to properly fix this, notify_push and test_client should always set a User-Agent header to something like notify_push/1.3.0 when making http requests. Any non-empty setting will do -- most anti-DDoS recipes look for empty and blacklisted User-Agent strings.