AuthenticationService FirebaseStrategy

[pictdare-dev]

hello friends i have a problem I want to use firebase authentication mark this mistake "The default Firebase app does not exist. Make sure you call initializeApp() "
const firebase = require('firebase-admin');
const { OAuthStrategy } = require('@feathersjs/authentication-oauth');
const { NotAuthenticated } = require('@feathersjs/errors');

const logger = require('./logger');

function initialize(app){
const firebaseConfig = app.get('firebase');

// Initialize app
try {
firebase.initializeApp({
credential: firebase.credential.cert(firebaseConfig)
});
} catch (e) {
console.log('erorr initializing firebase', e);
}
}
---I took the code from the feathers documentation

thanks friends for your help