Authy recently announced OneTouch, which will provide a single-tap Watch or mobile device login like Duo Security's but available for integration into websites and apps.
AgileBits'1Password (free on iOS) is best known as a password storehouse and generator, as well as keeping track and autofilling credit-card and other information. Its integration into iOS 8 using an extension started good and got better, and many apps now integrate in iOS to pull 1Password-stored logins directly.
But 1Password added support for one-time passwords in iOS in January and in OS X in April as a second step in verifying identity. The 1Password Watch app can display entries that are set in the iOS version by tapping Add to Apple Watch. (The addition is made via a tag, so you can manually add "Apple Watch" as a tag in the OS X release for the same effect.)
For any entry that has both a password and a TOTP, 1Password cleverly shows just the one-time code on the Watch.
The $10 Pro in-app purchase is necessary for Watch features. The OS X app costs $50 for a single-user license.
Lockdown ($4) is another entrant in this category, but has a few unique aspects. First, it lets you preserve the seed codes for a TOTPs. There are risks associated with that, but given that few apps and ecosystems let you recover those original codes without resetting your entire two-step or two-factor login at a site or through a service, it's worth considering. (In testing these apps, I wish I'd had such copies!)
Second, it can speak codes aloud from the phone, which is extremely useful. It's almost always perfectly safe to have a code shared (see the screen captures in this article) or spoken aloud because they are only good during a very brief window of time and still require the other account credentials to use. I hope to see this feature come to the Watch when developers are able to access the Watch's features fully later this year.
Favorite an item in iOS and it appears in the list on the Watch. The app is currently available only for iOS, but a Mac version is coming this month.
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