Let me introduce my small side project.
https://crates.io/crates/cargolifter
It's another crate registry but with a different approach for authentication.
Where do you want to store your company internal crates? Very likely in GitHub or GitLab. Therefore I'm using those as backend. You do your cargo login with your access token and you are allowed to write to GitHub/GitLab you are allowed to publish a crate.
Feedback and ideas are welcome. Thanks