With these changes the multilogin is optional for the plugin. So you can use clientId (required) + username (optional, empty string for "undefined" value) to store the shared preference.
The Key for the shared preference is clientid+username and the encrypt string is clientid+username+":"+password. In this way the multilogin is optional and not required, the developer can choose to use or not.
I included your changes with other revisions I made. I decided to remove the FingerprintAuth.show() method in favor of separate methods for encryption and decryption.
With these changes the multilogin is optional for the plugin. So you can use clientId (required) + username (optional, empty string for "undefined" value) to store the shared preference. The Key for the shared preference is clientid+username and the encrypt string is clientid+username+":"+password. In this way the multilogin is optional and not required, the developer can choose to use or not.