My website has only need for the login type that custom social connection provides.
I have setup Auth0.js, it redirects to login and everything. No errors shown, but it returns blank on userInfo. Most likely due to it having no users.
Is it any way I can create the user, when I only use custom social connection?
Technically, when you use social authentication then the end-user profile is automatically created in Auth0 at the first authentication completed by the end-user so there is no way for you to manually create the end-user profile. Administrative creation of end-user is only available for connection where Auth0 manages the credentials themselves like what it would be the case for database connections.
Having said that, the underlying issue about not returning any user information is likely related to something else. Have in mind that only the user information you request (and is available) will be included in the issued ID token or available upon request to the /userinfo endpoint. In particular, if you make an OIDC authentication request including just the openid scope then the only information requested is the user identifier; on the other hand, if you request the email and profile scopes then both email address information and also profile related properties like name will be returned if available.
In conclusion, in order to troubleshoot the situation you should update your question with the Auth0.js configuration you’re using and also include the social provider being used as some may not return the user information in question.