> I don't understand why authentication usually requires you to type in some 6-digit number from your phone.
Because it proves that the user logging in is in control of a device that they've linked to the account. When you add an account to whatever app you're using (Google Authenticator, Authy, etc.) what it's actually doing is receiving a cryptographic key that it uses to generate the 6 digit code based on the current time. Without that key, the proper 6 digit code can't be generated.
Because it proves that the user logging in is in control of a device that they've linked to the account. When you add an account to whatever app you're using (Google Authenticator, Authy, etc.) what it's actually doing is receiving a cryptographic key that it uses to generate the 6 digit code based on the current time. Without that key, the proper 6 digit code can't be generated.