Auth0 User Store
Auth0 provides the database infrastructure to store your users by default. This scenario provides the best performance for the authentication process since all data is stored in Auth0.
The Auth0-hosted database is highly secure. Passwords are never stored or logged in plain text but are hashed with bcrypt. Varying levels of password security requirements can also be enforced. To learn more, read Password Strength in Auth0 Database Connections.
Migrating to Auth0 from a custom user store
In this scenario, you have a legacy user store and wish to switch to the Auth0 store. Auth0 provides an automatic migration feature that adds your users to the Auth0 database one-at-a-time as each logs in and avoids asking your users to reset their passwords all at the same time. To learn more, read Configure Automatic Migration from Your Database.