In the bottom of the Human Interface Guidelines for Authentication is states that you should not use custom icons for TouchID/FaceID:
Don't use custom icons to identify system authentication features. When people see icons that look like the system's Touch ID (thumbprint) and Face ID icons, they think they're supposed to authenticate. Custom variants of these icons create inconsistency and cause confusion, especially when colorized, displayed at a large size, and presented out of context—like as a button label or on an app's Settings screen.
However, there are no links or references to a library of icons to use for TouchID/FaceID - so how am I going to obtain Apple sanctioned versions of these icons?