They have a share sheet extension. Click the thing you use to email a webpage, click the 1Password button, log in, click the log in that's detected to match the URL, autofills and you can hit submit.

Password fields can't use custom keyboards because of fear of logging that entry. The share sheet extension works great though for 1Password, especially when combined with TouchID.

If you're using iOS i'm pretty sure that custom keyboards aren't allowed to access the password fields?

the android beta has this as well