The main problem in our scenario is that we use a on premises SonarQube, not sonarcloud. Due that, allow access from internet using a token, is a security breach in case some bug is present somewhere. If someone with a token, knows how to explore some breach in SonarQube, maybe it will allow the person to reach the source code or our internal network. It is really hard to do, but the security team cannot consider the risk.
Anyway, in another post I posted that I implemented a way to have mtls using this scanner. Also I submitted a PR to the scanner, also linked in that post.