...
To set up or manage 2-factor authentication for your account, navigate to Options -> User Preferences and click on the "2-factor authentication" button.
This window will display the current status of 2-factor authentication on your account and list your registered devices. To enable 2-factor authentication, you must register at least one device.
...
To register a new device click on the "Register new device..." button. You will be prompted to enter a name for your device. Choose something that will allow you to remember what device you are registering (e.g. "my iphone 7"). Then press "Next".
A Q/R code will appear on the screen. You will need to scan this code with your authenticator app to register your OnePacs account.
Enter a 6-digit passcode generated by your mobile device and click "Verify" to continue. At this point 2-factor authentication will be enabled for your account and you will be prompted to enter a passcode on your next login.
Temporarily suspending 2-factor authentication
...