Handling User Forms and Authentication

Tutorial 3 of 5

1. Introduction

Tutorial Goals

This tutorial aims to guide users on how to handle user forms and implement authentication in a Flask application. We'll discuss form data validation and user session management, which are essential for creating secure and user-friendly web applications.

Learning Outcomes

By the end of this tutorial, you should be able to:
- Handle user forms in Flask.
- Implement authentication and create login and logout functionality.
- Validate form data.
- Manage user sessions.

Prerequisites

Before starting this tutorial, you should have a basic understanding of Python and Flask. Familiarity with HTML/CSS might also be beneficial but is not necessary.

2. Step-by-Step Guide

Handling User Forms in Flask

Flask-WTF is an extension that integrates the WTForms library with your Flask application. It makes handling forms easy.

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField
from wtforms.validators import DataRequired, Length, Email, EqualTo

class RegistrationForm(FlaskForm):
    username = StringField('Username', validators=[DataRequired(), Length(min=2, max=20)])
    email = StringField('Email', validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])
    confirm_password = PasswordField('Confirm Password', validators=[DataRequired(), EqualTo('password')])
    submit = SubmitField('Sign Up')

Authentication

Flask-Login is a useful extension for user authentication. It provides user session management, which means it handles the common tasks of logging in, logging out, and remembering users’ sessions over extended periods.

from flask_login import UserMixin, login_user, current_user, logout_user, login_required

@app.route("/login", methods=['GET', 'POST'])
def login():
    if current_user.is_authenticated:
        return redirect(url_for('home'))
    form = LoginForm()
    if form.validate_on_submit():
        user = User.query.filter_by(email=form.email.data).first()
        if user and bcrypt.check_password_hash(user.password, form.password.data):
            login_user(user, remember=form.remember.data)
            return redirect(url_for('home'))
    return render_template('login.html', title='Login', form=form)

3. Code Examples

Registration Form

@app.route("/register", methods=['GET', 'POST'])
def register():
    if current_user.is_authenticated:
        return redirect(url_for('home'))
    form = RegistrationForm()
    if form.validate_on_submit():
        hashed_password = bcrypt.generate_password_hash(form.password.data).decode('utf-8')
        user = User(username=form.username.data, email=form.email.data, password=hashed_password)
        db.session.add(user)
        db.session.commit()
        return redirect(url_for('login'))
    return render_template('register.html', title='Register', form=form)

Logout

@app.route("/logout")
def logout():
    logout_user()
    return redirect(url_for('home'))

4. Summary

In this tutorial, we have covered how to handle user forms, implement authentication, validate form data, and manage user sessions in a Flask application.

5. Practice Exercises

Create a user registration form with additional fields like 'First Name', 'Last Name', and 'Age'. Validate the data accordingly.
Implement a 'Remember Me' feature in the login form. The Flask-Login extension can help with this.
Create a 'Forgot Password' feature that sends a reset link to the user's email.

Remember, the best way to learn is by doing. So, try to complete these exercises without looking at the solutions. Don't worry if you get stuck, that's part of the learning process!