When using email + password authentication with database connections, does Auth0 require a unique email address per user? What about when using username + password authentication? Does Auth0 also require a unique email address per user in this case?
Auth0 enforces uniqueness of the email/username within a connection. For example, you can’t have two users with the same email address in the same connection (such as a regular DB email/password connection), but you can have two users with the same email address if they belong to different connections, such as a social connection and a regular DB email/password connection. For this case, you may use account linking to ensure uniqueness across connections as well: