How do I add add a SAML/WS-Fed identity provider to user flow via microsoft graph in entra external ID?

I have an user flow for my SaaS app with entra external id as my IDP, and I need to have a feature in my app which my costumers can add their SAML/WS-Fed IDPs and log in with their identities.

As far as I know, I can configure federation via microsoft graph (https://learn.microsoft.com/en-us/entra/external-id/direct-federation), but in the docs it's stated I need to link the identity to the user flow in external ID so users can log in using it, but I didn't find how it can be done via microsoft graph, only in the entra ID admin center (https://learn.microsoft.com/en-us/entra/external-id/customers/how-to-saml-ws-federation-self-service-sign-up). How can I do it?