How to setup an authentification system through Flask and the Flask-Login extension. The database backend is a MySQL one and the ORM is SQLAlchemy (Flask-SQLAlchemy extension). It only check if a user exists and if the given password is the good one. No credentials verification.

__init__.py

from application import app

# Configuration setup
from kuchiyose import config
app.config.from_object(config.DevelopmentConfig)

# SQL Alchemy setup
from flask.ext.sqlalchemy import SQLAlchemy
db = SQLAlchemy(app)

# Flask-Login setup
from flask.ext.login import LoginManager
login_manager = LoginManager()
login_manager.login_view = "login"
login_manager.session_protection = "strong"
login_manager.setup_app(app)

import views

flask-login-example.py

from Foo import app, login_manager
from models import User
from forms import LoginForm

from flask import (render_template, redirect, 
                   url_for, request, 
                   g)
from flask.ext.login import (login_user, logout_user, 
                             current_user, login_required)
                             
@login_manager.user_loader
def load_user(userid):
    """Flask-Login user_loader callback.
    The user_loader function asks this function to get a User Object or return 
    None based on the userid.
    The userid was stored in the session environment by Flask-Login.  
    user_loader stores the returned User object in current_user during every 
    flask request. 
    """
    return User.query.get(int(userid))


@app.before_request
def before_request():
    """Will be executed before each request."""
    g.user = current_user
    
@app.route('/')
def blog_index():
    return "awesome index"
    
    
@app.route('/admin/')
@login_required
def admin_root():
    return "awesome admin"


@app.route('/admin/login/', methods=['GET','POST'])
def login():
    """Logs a user in.
    We try to catch a user with the given username. If a user exists, 
    he's logged in, else, we return a login error.
    """

    if g.user is not None and g.user.is_authenticated():
        return redirect(url_for('admin_root'))
    
    form = LoginForm()
    
    if request.method == "POST" and form.validate_on_submit():
        username = form.username.data
        password = form.password.data
        remember_me = form.remember_me.data
    
        try:
          user = User.get(username)
        except:
          user = None
    
        if user and user.check_password(password):
            login_user(user, remember_me, force=True)
            return redirect(request.form['next'] or url_for("admin_root"))     
        else:
            error = 'Username/Password incorrect.'
            return render_template('login.html.j2', 
                form=form,
                title='Sign In',
                error=error)
    
        return render_template('login.html.j2',
            form=form,
            title='Sign In')


@app.route('/admin/logout')
def logout():
    logout_user()
    return redirect(url_for('index'))