How to modify login request to add more parameter and SSO checking

I want to modify the server code which is downloaded from https://github.com/bitwarden/server, to add 2 new function based our requirement , then I can deploy the new function to the server in ourselves host server.

  1. add a parameter in Login requst

  2. add SSO checking in login processing.

My question is: which code should I modify? I did not found the code, which class.

thanks a lot.