• Flask pip install flask
• Flask-Login pip install flask-login

• Initialize the flask app with app=Flask(__name__)
• Set a secret key, Flask-Login uses sessions and sessions in Flask need a secret Key
• Create an instance of LoginManager class login_manager = LoginManager()
• Initialize the LoginManager with the app that was created login_manager.init_app(app)
• In your User model, implement the UserMixin from Flask-Login class User(UserMixin) and implement the required methods: is_authenticated, is_active, is_anonymous and get_id
• Decorate a method with @login_manager.user_loader that returns the User object given the ID
• In the login end point, once the app side validation is done, register the user into Flask-Login with the login_user method. login_user(userDAO.get(user_name)). This would register a session with that user
• After that, any route that needs authentication can be decorated with @login_required and Flask-Login takes care of the rest
• To logout, call the logout_user() method
• To get the current user's ID the current_user.get_id() method can be used. If there is no one logged in, current_user.get_id() would return None

DONE.

I've written one small repo that illustrates this over here