We want this login/signup UX in a mobile app:
- ask user for email address
- if the user is registered, check the identity provider used by the specific user and redirect to that idp for login (via appauth).
- if the user is not registered, send user to keycloak register page
We could build it using our spring boot backend that uses the keycloak API. But I wonder if this is possible without a custom backend? If keycloak does not support it out-of-the-box we would be happy to write a custom SPI or so for it.
The idea is to not hint the id provider (as supported to skip the login page via kc_idp_hint=google), but we do want to hint the email address. Keycloak then should find out the used idp (or plain email/pw) and send the user to the respective login/signup system.
Is there any solution like this on the market? How could we build that otherwise?