def create_app():
    """ Flask application factory """
    
    # Setup Flask and load app.config
    app = Flask(__name__)
    app.config.from_object(__name__+'.ConfigClass')

    # Setup Flask-MongoEngine
    db = MongoEngine(app)

    # Define the User document.
    # NB: Make sure to add flask_user UserMixin !!!
    class User(db.Document, UserMixin):
        active = db.BooleanField(default=True)

        # User authentication information
        username = db.StringField(default='')
        password = db.StringField()

        # User information
        first_name = db.StringField(default='')
        last_name = db.StringField(default='')

        # Relationships
        roles = db.ListField(db.StringField(), default=[])

    # Setup Flask-User and specify the User data-model
    user_manager = UserManager(app, db, User)

    # The Home page is accessible to anyone
    @app.route('/')
    def home_page():
        # String-based templates
        return render_template_string("""
            {% extends "flask_user_layout.html" %}
            {% block content %}
                <h2>Home page</h2>
                <p><a href={{ url_for('user.register') }}>Register</a></p>
                <p><a href={{ url_for('user.login') }}>Sign in</a></p>
                <p><a href={{ url_for('home_page') }}>Home page</a> (accessible to anyone)</p>
                <p><a href={{ url_for('member_page') }}>Member page</a> (login required)</p>
                <p><a href={{ url_for('user.logout') }}>Sign out</a></p>
            {% endblock %}
            """)

    # The Members page is only accessible to authenticated users via the @login_required decorator
    @app.route('/members')
    @login_required    # User must be authenticated
    def member_page():
        # String-based templates
        return render_template_string("""
            {% extends "flask_user_layout.html" %}
            {% block content %}
                <h2>Members page</h2>
                <p><a href={{ url_for('user.register') }}>Register</a></p>
                <p><a href={{ url_for('user.login') }}>Sign in</a></p>
                <p><a href={{ url_for('home_page') }}>Home page</a> (accessible to anyone)</p>
                <p><a href={{ url_for('member_page') }}>Member page</a> (login required)</p>
                <p><a href={{ url_for('user.logout') }}>Sign out</a></p>
            {% endblock %}
            """)

    return app
Flask application factory