The entire login process occurs between you and Mojang's servers. Technic is never part of the login process.
The launcher is open source; you can find the repo here: https://github.com/TechnicPack/LauncherV3
The code related to Mojang login: https://github.com/TechnicPack/LauncherV3/blob/master/src/main/java/net/technicpack/minecraftcore/mojang/auth/AuthenticationService.java#L97:L111
