Fingerprint sensors have been a thing on Android for a while, and Google has had official API support in Android for more than a year. Still, there are some apps that inexplicably lack support for fingerprint security. Mint was one of them until today. This app has finally been updated with a fingerprint security option.
If you mosey into the security settings of the latest version, Mint includes an option to enable fingerprint unlock. That means you'll have to tap a registered fingerprint on the sensor each time you open the app. It's faster than typing in a PIN every time, but be aware anyone with a registered fingerprint on your phone will be able to access your Mint data.
The update also includes bug fixes (duh) and a tweak to the refresh settings. You can't toggle automatic 4-hour refresh in the settings anymore. The app still does that, it's just always activated.