Need to publish RMTP stream, but it requires token

[toboil-features]

Question

I wanna put in WebRTC with Simulcast and output RTMP stream to rtmp://localhost:21001/live, but I don't know how to fit required token right.

I tried:

paths:
  proxied:
    # url of the source stream, in the format rtmp://user:pass@host:port/path
    source: rtmp://localhost:21001/live

But outputs ERR [path proxied] [RTMP source] EOF

I already tried to specify password, as an option (still EOF error):

paths:
  proxied:
    # url of the source stream, in the format rtmp://user:pass@host:port/path
    source: rtmp://user:KmNPBhHw@localhost:21001/live

The problem that the end server (RMTP) does not demands username but MediaMTX mandates username to be specified, else it'll not run.
ERR: username and password must be both provided

[toboil-features]

Both of these configs trigger "invalid streaming key; rejecting incoming stream from localhost:48992" at the end RMTP side, which, in theory, needs the end token to accept MediaMTX stream.

[toboil-features]

Token thing is being embedded like: rtmp://localhost:21001/live/KmNPBhHw
At least in my case.