Firebase - Recognize user auth from iOS App to Web Page

I have an iOS app and a web page both using firebase.

The user is currently logged in and verified on the iOS app. (Swift)

if Auth.auth().currentUser?.uid != nil {
    
     //user is logged in
}

The user is then redirected from the iOS app to a designated web page.

iOS App -> myfirebasewebpageexample.com

How can I recognize that current user sent from the iOS app to the web page without having to re-authenticate the user with credentials? (email, Password)

<script>

    //https://firebase.google.com/docs/auth/web/manage-users
    
    // Returns true if a user is signed-in.
    function isUserSignedIn() {

        firebase.auth().onAuthStateChanged(function(user) {
            if (user) {
                // User is signed in.
            } else {
                // No user is signed in.
            }
        });
    }


</script>

Programming Languages:

• Swift

• Javascript