(#m443x2q) oki got it

curl -X 'POST' -d '{"username":"test","password":"test"}  ' -H 'Accept: application/json' -H 'Content-Type: application/json' -H 'User-Agent: go.yarn.social/1.0.0@HEAD' 'https://twtxt.net/api/v1/auth' | jq '.token'

But now I realise, that I can’t inject it on twtr :S>
At least i had fun debugging yarnc and yarnd code.
Thanks