maxcountryman/flask-login

Flask-Login is a Python library for the Flask web framework that handles the mechanics of logging users in and out of a web application. When someone visits a site built on Flask, Flask-Login tracks whether they are signed in across multiple page requests, a task that would otherwise require writing a lot of repetitive session-handling code from scratch. The library does not come with a built-in user database or a fixed way of storing passwords. Instead, it asks the developer to define a user object with a few standard methods, then provide a function that can look up a user by their ID. This design means it works equally well with SQL databases, document stores, flat files, or any other storage the developer prefers. Once connected to a Flask app, Flask-Login provides a small set of tools that cover most login scenarios. A login_required decorator blocks access to any route unless the visitor is authenticated, redirecting anonymous users elsewhere. The login_user and logout_user functions handle starting and ending sessions. A current_user proxy is available anywhere in a request, letting templates and views check who is signed in without passing the user object around manually. The library also supports a "remember me" option that keeps a user logged in across browser restarts through a long-lived cookie. This is opt-in, and the developer controls how long the session lasts. Flask-Login has been around for many years and is a widely used choice for Flask applications that need basic authentication without pulling in a larger framework. Full documentation is available at flask-login.readthedocs.io.