I want to use Auth0 in my jovo app for Alexa-skill as well as Google-Action. I have an existing api to login the user, it returns a token which can then be used with other api calls to get more user information from my backend.
So I was thinking about using Auth0 to provide users to fill in their existing username/password and then Auth0 routes it to my login api and returns the token.
If you have an existing username/password database that you want to keep, or want to slowly migrate over to Auth0 without having to send out password reset emails to everybody, you can use a custom database, optionally with the migration turned on.