To save passwords, you need to enable a system-wide Password Manager service, such as AutoFill by Google. Saving passwords via AutoFill is fully supported by Hermit.
That’s it, you’re done.
Now go back to Hermit, and when you browse, you will be asked to save passwords when you login for the first time. Enabling AutoFill by Google will also enable saving passwords in many other apps and browsers besides Hermit.
If you do not want to use AutoFill by Google, you can use other password managers, but some may have issues. Please contact the developers of those apps to include support for Hermit.