Destroy Activity after leaving it

I need to destroy an activity that have fragments with the login methods when i go to the mainactivity. I already tried flags, supportfragmentmanager but didn't works. Please, if anyone know how to do this tell me, please!

The signIn fragment is inside the AuthenticationActivity Going to MainActivity Code:

val intent = Intent(context, MainActivity::class.java)
             startActivity(intent)

When i go to the MainActivity, i need destroy the entire AuthenticationActivity, beucause i don't need that the users do login because they are already logged.