frontend: sign up flow

[Iancam]

We're using auth0! look here for instructions: https://auth0.com/docs/quickstart/spa/react

sign-up flow:
click sign in ->
enter info:
- google, facebook (use auth0 signup api?)
or
- email
- pw
button: sign in

not a user yet?
button: sign up

-> user logged in, looking at my books