I’m trying to integrate Microsoft Entra External ID for our Signup flow.

I have created a custom Rest API for handling the AttributeCollectionStart event (event from the Custom Authentication Extensions).
On this REST API, I want to check if the user who is in the signup flow is authorized to use the application (we have a list in database with authorized email address), then pre-fill the attributes from this database by searching the user using the email address.

When registering a user with email address, the flow is working well : I’m able to get the email address from this field :

"identities": [ { "signInType": "emailAddress", "issuer": "myapp.onmicrosoft.com", "issuerAssignedId": "[email protected]" } ]

The problem is when registering with Google Provider, I’m only getting a google identifier (I think it is, I’m not sure) :

"Identities": [ { "Issuer": "google.com", "IssuerAssignedId": "117008053156718551476", "SignInType": "federated" } ]

Is there a possibility to retreive the email in the signup process ?
Is Microsoft Graph will work for this use case ? (never used it).

It work with default provider (email), but not google provider.