Firebase Admin SDK : Verifying ID tokens from the REST API

Question

I'm trying to verify Id tokens received by signing in with the REST API for authentication by using the verifyIdToken(idToken) method in the Admin SDK but instead of getting the decoded token I get the error:

Firebase ID token has incorrect "iss" (issuer) claim. Expected "https://securetoken.google.com/"" but got "https://identitytoolkit.google.com/". Make sure the ID token comes from the same Firebase project as the service account used to authenticate this SDK. See https://firebase.google.com/docs/auth/admin/verify-id-tokens for details on how to retrieve an ID token.

As I said above I'm getting my token from the REST API, so I was expecting this to work. The response I get from the API is this:

{
    "kind": "identitytoolkit#VerifyPasswordResponse",
    "localId": "pu0yjIc8tnR85X2gERdtLx684DK2",
    "email": "test@test.com",
    "displayName": "",
    "idToken": "<token-id>",
    "registered": true
}

Is this considered a custom token? if so, how can I verify it?

Answer 1

As of Sep 2018, the issuer of the ID Token returned by REST API seems to be changed from https://identitytoolkit.google.com/ to https://securetoken.google.com/. And I can successfully verify this id token in firebase admin SDK.

[Edit]: The firebase admin SDK still fails to verify the Facebook ID Token returned by identitytoolkit's verifyAssertion REST API.