I had no idea developers could use the 1Password iOS extension to prefill one-time passwords in addition to regular usernames and passwords in their apps:
Did you know that our App Extension API supports one-time passwords? In fact, it’s been there since version 1.5 of the API. If you haven’t already, I recommend that you upgrade to the latest version, 1.6.1. Not only can your users fill their usernames and passwords in your app with a few simple taps, their one-time passwords can be filled just as easily.
I use the 1Password extension every day (it has strong app support at this point), but I've never come across apps that supported one-time passwords as well. Speaking of which, it's always a good time to switch from Google Authenticator or Authy to 1Password.