Most customers use the Auth0 Universal Login Page (ULP), which comes with both login and signup option. In the authorization request, it’s also possible to make the Auth0 signup tab / signup page show up by default (instead of the login).
This is both possible with the Auth0.js and also with the SPA SDK.
webAuth.authorize({'mode': 'signUp'});
plus a change in the Auth0 login page itself, see this thread for details:
We usually encourage customres to use a redirect flow over an embedded one, both for login and signup. The Pros and Cons are described on Centralized Universal Login vs. Embedded Login