According to reports, WhatsApp could be working on a fingerprint authentication feature to protect chats. Once implemented, users may have to authenticate themselves to be able to use WhatsApp. WABetaInfo claims to have spotted this feature, which it says is disabled by default in WhatsApp for Android beta version 2.19.3.
Reports say this feature will be available within the app under Settings > Account > Privacy. Once enabled, this features is expected to prevent others from accessing your WhatsApp. Many OEMs these days offer built-in app lock (either pattern / PIN lock or fingerprint authentication).
In the event that you have a similar third-party authentication in place already, you may not require additional authentication. Users may also have to authenticate their identity while trying to access WhatsApp from notifications.