Fingerprint authentication in Debian Stretch
Supported devices https://www.freedesktop.org/wiki/Software/fprint/libfprint/
Packages needed are: fprintd, libpam-fprintd and if you want to test your reader, there is a GUI program fprint-demo.
First run fprintd-enroll, by default right index finger is read, if you want use other finger, there is -f option, man fprintd.
Finger is read five times. To check, use fprintd-verify.
Next time you login, lightdm after username asks you to read your fingerprint. Be ready, timeout by default is quite short. You can repeat step if needed. Password login is also possible, if your fingerprint is not recognized.