How have you got it hooked up? Is the RP configured to talk to ADFS and then ADFS has AAD as a CP? That’s the way to do it. Then the app. will go to ADFS and you see a Home Realm Discovery screen. You pick AAD, authenticate and get redirected back to the app. It’s a configuration issue not a claims rule issue.
SAML is not designed for SPA.
“The SAML SSO flows were designed with a browser in mind sending SAML messages to a web application either as HTTP redirects or HTTP Posts. Authentication sessions are then established in this browser session.”
You mean with SAML? I wouldn’t recommend that. Have a look at:
So you want the path:
App → idsrv4 → B2C ?
In this case B2C would act like a social provider to idsrv4 i.e. exactly the same as adding Google. This uses OpenID Connect.
The user would see another tab on the login screen.