Using Flask-Login for Session Management and Authentication in Flask Applications

Flask‑Login provides user session management and route protection for Flask applications. The basic configuration is documented on the wiki, and this tutorial walks through a practical example.

1. Installation pip install flask-login 2. Initialization

Initialize Flask‑Login inside the app factory function and import login_manager in the model module.

3. Model configuration

Create user and role models that inherit from UserMixin, and implement the required methods (e.g., get_id()) which return a unique Unicode string for the user.

4. Route configuration and usage

In routes, use the login_required decorator to restrict access to authenticated users. Example login and logout implementations are shown using jQuery and Flask.

5. Template usage

In Jinja templates you can check authentication and display the current user's name:

{% if current_user.is_authenticated() %}<br/>Hi {{ current_user.name }}!<br/>{% endif %}

6. Common issues

• Unauthenticated users accessing protected URLs – set login_manager.login_view = 'auth.login' or customize with @unauthorized_handler. • Controlling session expiration – configure Flask‑Login settings accordingly. • Forcing a fresh login (e.g., after password change) – use @fresh_login_required. • Handling API keys or custom headers – implement @login_manager.request_loader.

Throughout the guide, several diagrams illustrate the flow of authentication, session handling, and template rendering.