authentication
Proof that a person is who they say they are before your app lets them in.
Like showing ID at a door, authentication is how a user proves who they are before an app lets them in.
This matters because private data must stay tied to the right person, and actions like payments must be safe. Supabase provides signup, login, and a session, the period after sign in when the app remembers you.
In practice, it looks like sign in screens, email magic links or codes, and a short token, a small string that proves you are signed in, sent with each API call.