TURN REST API: Error parsing API from Janus

[ehfd]

CC @fancycode

Issue number one: The TURN REST API capability provided by the signaling server is not well documented, when one must use TURN with Janus.

nextcloud-spreed-signaling/backend_server.go

Line 180 in 4e34e97

r.HandleFunc("/turn/credentials", b.setComonHeaders(b.getTurnCredentials)).Methods("GET")

Documentation should specify correctly that they should add the turn_rest_api option in Janus pointing to /turn/credentials for janus.jcfg in order to utilze turn_rest_api_key:

nat: {
    stun_server = "stun.myurl.invalid"
    stun_port = 3478
    full_trickle = true
    turn_rest_api = "http://localhost:8080/turn/credentials"
    turn_rest_api_key = "<REDACTED>"
}

Issue number two:

Directly accessing http://localhost:8080/turn/credentials?service=turn&api=<REDACTED>&key=<REDACTED>&username=example (same format as https://github.com/meetecho/janus-gateway/blob/dc8323741043a75537fb770d42ca37498a3d8947/src/turnrest.c#L140) results correctly in:

{"username":"1700000000:example","password":"<REDACTED>","ttl":86400,"uris":["turn:turn.myurl.invalid:3478?transport=udp","turn:turn.myurl.invalid:3478?transport=tcp"]}

But in Janus:

[ERR] [turnrest.c:janus_turnrest_request:198] Couldn't parse response: error on line 1: '[' or '{' expected near end of file
[WARN] [{REDACTED}] Failed to add some remote candidates (added 0, expected 1)

Therefore, the TURN REST API is not usable, possibly an empty response for some reason?

[fancycode]

If you increase the log level in Janus, you should see what was received:
https://github.com/meetecho/janus-gateway/blob/dc8323741043a75537fb770d42ca37498a3d8947/src/turnrest.c#L192-L194