Right now, the feature is only available to those using WhatsApp Beta App. Although around February, WhatsApp rolled out the authentication feature for iOS users, making it possible to unlock the App using Touch ID.
Android Beta users running version 2.19.221 can now catch in on the feature by going to Settings > Account > Privacy > Fingerprint lock to enable the new feature. When enabled, you will then be able to unlock WhatsApp with your fingerprint. Enabling this new feature provides extra security for your chats, and WhatsApp uses Android biometric authentication APIs, which means you don’t have to worry about Facebook or any third party app having access to your fingerprint data.
When the feature is enabled, you will need to use your fingerprint to unlock WhatsApp every time you launch the app, however, you can set a timer for it to lock automatically – you can either set it to after 1 minute or after 30 minutes.
Also, the fingerprint lock feature has a Show Content in Notification option that enables users to answer WhatsApp calls, preview and respond to messages or hide messages from the notification panel even when the Fingerprint lock is enabled.