SuperTokens is an open source authentication solution offering features like: Different types of login: Email / password, Passwordless (OTP or Magic link based).

SuperTokens.com

Maybe that's a dumb question, but what is the preferred way to save additional user information (name, profile image etc.) . I saw that you can add custom fields, but wouldn't it make sense to create a user in the application db to store additional information with the generated userId from supertokens? Do you recommend to use an own db for supertokens or to integrate into the application database?

It’s most flexible if you store the user info in your own db against the user id that supertokens generates. See the post sign up operations section in our docs.