I’m trying to use google’s calendar API and I’m so lost. I figured out how to get authentication the first time around, when I send the user to approve the access scope, but I can’t figure out how to get the credentials I need to perform any other actions once the session for that original authorization goes away. Here is all my code around connection to google.

def connect_to_google(user_id):

    flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(CLIENT_SECRETS_FILE, scopes=['https://www.googleapis.com/auth/calendar.app.created'])
    flow.redirect_uri = 'https://tb-read.com/createcalendar'
    authorization_url, state = flow.authorization_url(access_type="offline", include_granted_scopes="true", prompt="consent")
    session['state'] = state

    return redirect(authorization_url)```

@app.route('/createcalendar')
def create_calendar():
    """Create a new google calendar for the user"""

    if not g.user: 
        flash ('Please log in', 'danger')
        return redirect('/') 
    
    code = request.args.get('code')
    state = session['state']
    flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(CLIENT_SECRETS_FILE, scopes=['https://www.googleapis.com/auth/calendar.app.created'], state=state)
    flow.redirect_uri = url_for('create_calendar', _external=True)
    authorization_response = request.url
    flow.fetch_token(authorization_response=authorization_response)
    credentials = flow.credentials
    session['credentials'] = {
        'token': credentials.token,
        'refresh_token': credentials.refresh_token,
        'token_uri': credentials.token_uri,
        'client_id': credentials.client_id, 
        'client_secret': credentials.client_secret,
        'scopes': credentials.scopes
    }

    service = build('calendar', 'v3', credentials=credentials)
    calendar = {
        'summary': 'TB Read Calendar'
    }
    created_calendar = service.calendars().insert(body=calendar).execute()
    user = db.session.execute(db.select(User).where(User.user_id == g.user.user_id)).scalar()
    user.calendar_id = created_calendar['id']
    user.google_code = code
    db.session.add(user)
    db.session.commit()
    print('****************************')
    print(user.calendar_id)
    service.close()

    return redirect(f'/users/{g.user.user_id}/calendar')

@app.route('/api/posting', methods=['POST'])
def schedule_posting_days():
    """Schedule a user's posting schedule on the google calendar"""

    if not g.user: 
        flash ('Please log in', 'danger')
        return redirect('/') 
    
    last_post_date = request.json['lastPostDate']
    posting_frequency = request.json['postingFrequency']

    flow = google_auth_oauthlib.flow.Flow.from_client_secrets_file(CLIENT_SECRETS_FILE, scopes=['https://www.googleapis.com/auth/calendar.app.created'])
    authorization_response = request.url
    flow.fetch_token(authorization_response=authorization_response, code=g.user.google_code)
    credentials = flow.credentials
    session['credentials'] = {
        'token': credentials.token,
        'refresh_token': credentials.refresh_token,
        'token_uri': credentials.token_uri,
        'client_id': credentials.client_id, 
        'client_secret': credentials.client_secret,
        'scopes': credentials.scopes
    }

    service = build('calendar', 'v3', credentials=credentials)
    ## Check if a posting date event currently exists
    existing_posting_event = db.session.execute(db.select(Event).where(Event.user_id == g.user.user_id).where(Event.eventcategory == 'Posting')).scalar()
    ## Delete remaining recurring posting events
    if existing_posting_event.google_event_id: 
        post_event = service.events().get(calendarId=g.user.calendar_id, eventId = existing_posting_event.google_event_id).execute()
        today = date.today()
        post_event['recurrance'] = [f'RRULE: FREQ=DAILY; COUNT=g.user.posting_frequency; UNTIL={today}']
        service.events().update(calendarId=g.user.calendar_id, EventId = existing_posting_event.google_event_id, body=post_event).execute()
    ## Add new posting date event
    event = {
        'summary': 'Posting Day',
        'start.date': last_post_date,
        'end.date': last_post_date,
        'recurrence': [f'RRULE: FREQ=DAILY; COUNT={posting_frequency}']
    }
    posting_day = service.events().insert(calendarId = g.user.calendar_id, body=event).execute()
    print('**************************')
    print(posting_day)
    service.close()
    ## Update user profile
    if g.user.posting_frequency != posting_frequency:
        user = db.session.execute(db.select(User).where(User.user_id == g.user.user_id)).scalar()
        user.posting_frequency = posting_frequency
        db.session.add(user)
        db.session.commit()

    return jsonify({'success': 'Posting Event Changed'})