How can I create a custom provider for my phone/OTP sign-in, yet integrate it with Keycloak and Qwik?

[Nefcanto]

I'm using Keycloak + Qwik + Auth.js, yet I can't develop Keycloak plugins (I am not a Java developer).
I created a phone/OTP sign-in page. This is my custom flow:

• User submits phone number
• OTP is created and sent (.NET API)
• User enters the OTP
• OTP is validated
• API (.NET) connects to the Keycloak and gets a JWT token for the user
• JWT is returned to Qwik

Now from here, I'm stuck. How can I give @auth/core that JWT token? How can I make @auth/core aware that it has to use Keycloak URLs for JWT-related stuff (refreshing the token, validating the token, etc.)? How can I know in my Qwik app that the user is signed in? How to get user's data?