AngularFireAuth.idToken is not valid for REST queries?

I'm being unable to get a Dynamic Link stats via

GET https://firebasedynamiclinks.googleapis.com/v1/SHORT_DYNAMIC_LINK/linkStats?durationDays=DURATION

Authorization: Bearer ID_TOKEN

Version info

Angular: 8.2.14

Firebase: 7.5.0

AngularFire: 5.2.3

How to reproduce these conditions

Steps to set up and reproduce

I'm trying to use the Angular Fire idToken and pass it to the HttpClient via interceptor:

@Injectable()
export class TokenInterceptor implements HttpInterceptor {
  constructor(public auth: MyAuthService) {}
  intercept(
    request: HttpRequest<any>,
    next: HttpHandler
  ): Observable<HttpEvent<any>> {
    request = request.clone({
      setHeaders: {
        Authorization: `Bearer ${this.auth.idToken}`
      }
    });

    return next.handle(request);
  }
}

The header is correctly sent but I'm getting 401

Debug output

Errors in the Network console

{
  "error": {
    "code": 401,
    "message": "Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.",
    "status": "UNAUTHENTICATED"
  }
}

Expected behavior

Looking at the API Authorization documentation, there's the scope https://www.googleapis.com/auth/firebase and I assume the AngularFire token is already authorized with it, but it's also curious that a response header of the error response is www-authenticate: Bearer realm="https://accounts.google.com/"

angular / angularfire