Building a Login System with Python Flask and MySQL for Beginners

File Structure

  
  \-- pythonlogin
  |-- main.py
  \-- static
    |-- style.css
  \-- templates
    |-- index.html
    |-- register.html
    |-- home.html
    |-- profile.html
    |-- layout.html
  

Each file will contain the following:

• main.py — This will be our main project file, all our Python code will be in this file (Routes, MySQL connection, validation, etc).
• index.html — Login form created with HTML5 and CSS3.
• register.html — Registration form created with HTML5 and CSS3.
• home.html — The home template to display for logged-in users.
• profile.html — The profile template to display for logged-in users.
• layout.html — The layout template for the home and profile templates.
• style.css — The CSS3 stylesheet for our login and registration system.

The below instruction will start your web server (Windows):

• Make sure your MySQL server is up and running, it should have automatically started if you installed it via the installer.
• Open Command Prompt, make sure you have the project directory selected, you can do this with the command cd c:\your_project_folder_destination on Windows.
• Run command: set FLASK_APP=main.py
• Run command: set FLASK_DEBUG=1
• Run command: flask run

Debug mode will allow us to edit our files without constantly restarting the web server.

2. Creating the Database and setting-up Tables

MySQL Workbench is a GUI for creating and editing our databases, follow the below instructions.

• Open MySQL Workbench
• Fill out your MySQL details
• Click Test Connection, if successful you can click OK
• Open your connection
• Execute the following SQL statements:

CREATE DATABASE IF NOT EXISTS `pythonlogin` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
USE `pythonlogin`;

CREATE TABLE IF NOT EXISTS `accounts` (
	`id` int(11) NOT NULL AUTO_INCREMENT,
  	`username` varchar(50) NOT NULL,
  	`password` varchar(255) NOT NULL,
  	`email` varchar(100) NOT NULL,
    PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

INSERT INTO `accounts` (`id`, `username`, `password`, `email`) VALUES (1, 'test', 'test', 'test@test.com');

The above SQL statement will create our database pythonlogin with the table accounts, it will also insert a test account, this account we’ll use for testing purposes later in the tutorial, it will make sure everything is working as it should.

3. Creating the Stylesheet (CSS3)

Edit the style.css file and add the following:

* {
  	box-sizing: border-box;
  	font-family: -apple-system, BlinkMacSystemFont, "segoe ui", roboto, oxygen, ubuntu, cantarell, "fira sans", "droid sans", "helvetica neue", Arial, sans-serif;
  	font-size: 16px;
  	-webkit-font-smoothing: antialiased;
  	-moz-osx-font-smoothing: grayscale;
}
body {
  	background-color: #435165;
  	margin: 0;
}
.login, .register {
  	width: 400px;
  	background-color: #ffffff;
  	box-shadow: 0 0 9px 0 rgba(0, 0, 0, 0.3);
  	margin: 100px auto;
}
.login h1, .register h1 {
  	text-align: center;
  	color: #5b6574;
  	font-size: 24px;
  	padding: 20px 0 20px 0;
  	border-bottom: 1px solid #dee0e4;
}
.login .links, .register .links {
  	display: flex;
  	padding: 0 15px;
}
.login .links a, .register .links a {
  	color: #adb2ba;
  	text-decoration: none;
  	display: inline-flex;
  	padding: 0 10px 10px 10px;
  	font-weight: bold;
}
.login .links a:hover, .register .links a:hover {
  	color: #9da3ac;
}
.login .links a.active, .register .links a.active {
  	border-bottom: 3px solid #3274d6;
  	color: #3274d6;
}
.login form, .register form {
  	display: flex;
  	flex-wrap: wrap;
  	justify-content: center;
  	padding-top: 20px;
}
.login form label, .register form label {
  	display: flex;
  	justify-content: center;
  	align-items: center;
  	width: 50px;
  	height: 50px;
  	background-color: #3274d6;
  	color: #ffffff;
}
.login form input[type="password"], .login form input[type="text"], .login form input[type="email"], .register form input[type="password"], .register form input[type="text"], .register form input[type="email"] {
  	width: 310px;
  	height: 50px;
  	border: 1px solid #dee0e4;
  	margin-bottom: 20px;
  	padding: 0 15px;
}
.login form input[type="submit"], .register form input[type="submit"] {
  	width: 100%;
  	padding: 15px;
  	margin-top: 20px;
  	background-color: #3274d6;
  	border: 0;
  	cursor: pointer;
  	font-weight: bold;
  	color: #ffffff;
  	transition: background-color 0.2s;
}
.login form input[type="submit"]:hover, .register form input[type="submit"]:hover {
  	background-color: #2868c7;
  	transition: background-color 0.2s;
}
.navtop {
  	background-color: #2f3947;
  	height: 60px;
  	width: 100%;
  	border: 0;
}
.navtop div {
  	display: flex;
  	margin: 0 auto;
  	width: 1000px;
  	height: 100%;
}
.navtop div h1, .navtop div a {
  	display: inline-flex;
  	align-items: center;
}
.navtop div h1 {
  	flex: 1;
  	font-size: 24px;
  	padding: 0;
 	margin: 0;
  	color: #eaebed;
  	font-weight: normal;
}
.navtop div a {
  	padding: 0 20px;
  	text-decoration: none;
  	color: #c1c4c8;
  	font-weight: bold;
}
.navtop div a i {
  	padding: 2px 8px 0 0;
}
.navtop div a:hover {
  	color: #eaebed;
}
body.loggedin {
  	background-color: #f3f4f7;
}
.content {
  	width: 1000px;
  	margin: 0 auto;
}
.content h2 {
  	margin: 0;
  	padding: 25px 0;
  	font-size: 22px;
  	border-bottom: 1px solid #e0e0e3;
  	color: #4a536e;
}
.content > p, .content > div {
  	box-shadow: 0 0 5px 0 rgba(0, 0, 0, 0.1);
  	margin: 25px 0;
  	padding: 25px;
	background-color: #fff;
}
.content > p table td, .content > div table td {
	padding: 5px;
}
.content > p table td:first-child, .content > div table td:first-child {
	font-weight: bold;
	color: #4a536e;
	padding-right: 15px;
}
.content > div p {
	padding: 5px;
	margin: 0 0 10px 0;
}

Feel free to customize the stylesheet, change text color, font sizes, content width, etc. This stylesheet will be used for all our pages (login, registration, home, and profile pages).

4. Creating the Login System

We can finally start coding with Python! What we’ll do in this part is create the login template, connect to MySQL database, login authentication, and create session variables.

The first thing we need to do is import the packages we’re are going to use, edit the main.py file and add the following:

from flask import Flask, render_template, request, redirect, url_for, session
from flask_mysqldb import MySQL
import MySQLdb.cursors
import re

Now we need to create some variables and configure the MySQL connection details.

Add after the above code:

app = Flask(__name__)

# Change this to your secret key (can be anything, it's for extra protection)
app.secret_key = 'your secret key'

# Enter your database connection details below
app.config['MYSQL_HOST'] = 'localhost'
app.config['MYSQL_USER'] = 'root'
app.config['MYSQL_PASSWORD'] = ''
app.config['MYSQL_DB'] = 'pythonlogin'

# Intialize MySQL
mysql = MySQL(app)

Make sure you change the MySQL details to your own details and change the secret key.

Now we can create the login page, to do that we need to create a new route.

Add after the above code:

# http://localhost:5000/pythonlogin/ - this will be the login page, we need to use both GET and POST requests
@app.route('/pythonlogin/', methods=['GET', 'POST'])
def login():
    return render_template('index.html', msg='')

Creating the Login Template

Edit the index.html file and add:

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>Login</title>
		<link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">
		<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.1/css/all.css">
	</head>
	<body>
		<div class="login">
			<h1>Login</h1>
			<div class="links">
				<a href="{{ url_for('login') }}" class="active">Login</a>
				<a href="#">Register</a>
			</div>
			<form action="{{ url_for('login') }}" method="post">
				<label for="username">
					<i class="fas fa-user"></i>
				</label>
				<input type="text" name="username" placeholder="Username" id="username" required>
				<label for="password">
					<i class="fas fa-lock"></i>
				</label>
				<input type="password" name="password" placeholder="Password" id="password" required>
				<div class="msg">{{ msg }}</div>
				<input type="submit" value="Login">
			</form>
		</div>
	</body>
</html>

As you can see with the login template we create the form with the input fields: username and password, and the form’s method is set to post, this will send the form data to our Python Flask server using a POST request.

If we navigate to http://localhost:5000/pythonlogin/ in our web browser it will look like the following:

If you click the Login button nothing will happen or will return an error, that’s because we haven’t yet set up the POST request that will process the form data.

Authenticating Users with Python

Now we need to go back to our main.py file and add the authentication code to our route function that we created.

After:

def login():

Add:

    # Output message if something goes wrong...
    msg = ''
    # Check if "username" and "password" POST requests exist (user submitted form)
    if request.method == 'POST' and 'username' in request.form and 'password' in request.form:
        # Create variables for easy access
        username = request.form['username']
        password = request.form['password']

With the code above we use an if statement to check if the requested method is POST and check if the username and password exist in the form request, if they both exist the username and password variables will be created.

Add after:

        # Check if account exists using MySQL
        cursor = mysql.connection.cursor(MySQLdb.cursors.DictCursor)
        cursor.execute('SELECT * FROM accounts WHERE username = %s AND password = %s', (username, password))
        # Fetch one record and return result
        account = cursor.fetchone()

The code above will select the account from our accounts table in our MySQL database with the username and password that the user entered in the login form.

Add after:

        # If account exists in accounts table in out database
        if account:
            # Create session data, we can access this data in other routes
            session['loggedin'] = True
            session['id'] = account['id']
            session['username'] = account['username']
            # Redirect to home page
            return 'Logged in successfully!'
        else:
            # Account doesnt exist or username/password incorrect
            msg = 'Incorrect username/password!'

This will check if the account exists, if it does we create new session variables, these session variables will be remembered for the user, we can use them to determine if the user is logged in or not.

Session variables act like cookies, they will be remembered on the server instead of the user’s browser, only the session ID will be stored as a browser cookie.

If the account doesn’t exist we can simply show an error on the login form.

Your login route should look like the following:

@app.route('/pythonlogin/', methods=['GET', 'POST'])
def login():
    # Output message if something goes wrong...
    msg = ''
    # Check if "username" and "password" POST requests exist (user submitted form)
    if request.method == 'POST' and 'username' in request.form and 'password' in request.form:
        # Create variables for easy access
        username = request.form['username']
        password = request.form['password']
        # Check if account exists using MySQL
        cursor = mysql.connection.cursor(MySQLdb.cursors.DictCursor)
        cursor.execute('SELECT * FROM accounts WHERE username = %s AND password = %s', (username, password))
        # Fetch one record and return result
        account = cursor.fetchone()
        # If account exists in accounts table in out database
        if account:
            # Create session data, we can access this data in other routes
            session['loggedin'] = True
            session['id'] = account['id']
            session['username'] = account['username']
            # Redirect to home page
            return 'Logged in successfully!'
        else:
            # Account doesnt exist or username/password incorrect
            msg = 'Incorrect username/password!'
    # Show the login form with message (if any)
    return render_template('index.html', msg=msg)

To make sure everything is working correctly navigate to http://localhost:5000/pythonlogin/ and input “test” in both the username and password fields, and then click the Login button, you should receive a message that outputs “Logged in successfully!”.

Creating the Logout Script

For a user to log out all we have to do is remove the session variables that were created when the user logs in.

Add the following code to the main.py file:

# http://localhost:5000/python/logout - this will be the logout page
@app.route('/pythonlogin/logout')
def logout():
    # Remove session data, this will log the user out
   session.pop('loggedin', None)
   session.pop('id', None)
   session.pop('username', None)
   # Redirect to login page
   return redirect(url_for('login'))

This will remove each session variable, without these session variables the user cannot be logged in. And then redirect the user to the login page.

To log out we can navigate to the following URL: http://localhost:5000/pythonlogin/logout

5. Creating the Registration System

We need a registration system so users can register on our app, what we’ll do in this part is create a new register route and create the registration template.

Creating the Registration Template

Edit the register.html file and add:

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>Register</title>
		<link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">
		<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.1/css/all.css">
	</head>
	<body>
		<div class="register">
			<h1>Register</h1>
			<div class="links">
				<a href="{{ url_for('login') }}">Login</a>
				<a href="{{ url_for('register') }}" class="active">Register</a>
			</div>
			<form action="{{ url_for('register') }}" method="post" autocomplete="off">
				<label for="username">
					<i class="fas fa-user"></i>
				</label>
				<input type="text" name="username" placeholder="Username" id="username" required>
				<label for="password">
					<i class="fas fa-lock"></i>
				</label>
				<input type="password" name="password" placeholder="Password" id="password" required>
				<label for="email">
					<i class="fas fa-envelope"></i>
				</label>
				<input type="email" name="email" placeholder="Email" id="email" required>
				<div class="msg">{{ msg }}</div>
				<input type="submit" value="Register">
			</form>
		</div>
	</body>
</html>

This is a basic registration template we’ll use to register users, it’s identical to the login template but also includes the Email field.

The form’s action attribute is set to the “register” route, we’ll use this route to handle the POST request.

Registering Users with Python

Now that we have our template created we can begin to create the “register” route, this will handle the POST request and insert a new account into our accounts table, only if the submitted fields are valid that is.

Go back to the main.py file and add the following:

# http://localhost:5000/pythinlogin/register - this will be the registration page, we need to use both GET and POST requests
@app.route('/pythonlogin/register', methods=['GET', 'POST'])
def register():
    # Output message if something goes wrong...
    msg = ''
    # Check if "username", "password" and "email" POST requests exist (user submitted form)
    if request.method == 'POST' and 'username' in request.form and 'password' in request.form and 'email' in request.form:
        # Create variables for easy access
        username = request.form['username']
        password = request.form['password']
        email = request.form['email']
    elif request.method == 'POST':
        # Form is empty... (no POST data)
        msg = 'Please fill out the form!'
    # Show registration form with message (if any)
    return render_template('register.html', msg=msg)

We create the “register” route and check if all the submitted form fields exist, if they don’t output a simple error.

After:

email = request.form['email']

Add:

        # Check if account exists using MySQL
        cursor = mysql.connection.cursor(MySQLdb.cursors.DictCursor)
        cursor.execute('SELECT * FROM accounts WHERE username = %s', (username))
        account = cursor.fetchone()
        # If account exists show error and validation checks
        if account:
            msg = 'Account already exists!'
        elif not re.match(r'[^@]+@[^@]+\.[^@]+', email):
            msg = 'Invalid email address!'
        elif not re.match(r'[A-Za-z0-9]+', username):
            msg = 'Username must contain only characters and numbers!'
        elif not username or not password or not email:
            msg = 'Please fill out the form!'
        else:
            # Account doesnt exists and the form data is valid, now insert new account into accounts table
            cursor.execute('INSERT INTO accounts VALUES (NULL, %s, %s, %s)', (username, password, email))
            mysql.connection.commit()
            msg = 'You have successfully registered!'

The above code will select an account with the submitted username and password fields, if the account doesn’t exist we can validate the data, the validation will check if the submitted email is valid and check if the username contains only letters and numbers.

If everything checks out the code will insert a new account into our accounts tables.

To test that it is working correctly navigate to http://localhost:5000/pythonlogin/register and fill out the form and click the Register button, you should get the following response:

# http://localhost:5000/pythinlogin/home - this will be the home page, only accessible for loggedin users
@app.route('/pythonlogin/home')
def home():
    # Check if user is loggedin
    if 'loggedin' in session:
        # User is loggedin show them the home page
        return render_template('home.html', username=session['username'])
    # User is not loggedin redirect to login page
    return redirect(url_for('login'))

{% extends 'layout.html' %}

{% block title %}Home{% endblock %}

{% block content %}
<h2>Home Page</h2>
<p>Welcome back, {{ username }}!</p>
{% endblock %}

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>{% block title %}{% endblock %}</title>
		<link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">
		<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.7.1/css/all.css">
	</head>
	<body class="loggedin">
		<nav class="navtop">
			<div>
				<h1>Website Title</h1>
                <a href="{{ url_for('home') }}"><i class="fas fa-home"></i>Home</a>
				<a href="{{ url_for('profile') }}"><i class="fas fa-user-circle"></i>Profile</a>
				<a href="{{ url_for('logout') }}"><i class="fas fa-sign-out-alt"></i>Logout</a>
			</div>
		</nav>
		<div class="content">
			{% block content %}{% endblock %}
		</div>
	</body>
</html>

return 'Logged in successfully!'

return redirect(url_for('home'))

# http://localhost:5000/pythinlogin/profile - this will be the profile page, only accessible for loggedin users
@app.route('/pythonlogin/profile')
def profile():
    # Check if user is loggedin
    if 'loggedin' in session:
        # We need all the account info for the user so we can display it on the profile page
        cursor = mysql.connection.cursor(MySQLdb.cursors.DictCursor)
        cursor.execute('SELECT * FROM accounts WHERE id = %s', [session['id']])
        account = cursor.fetchone()
        # Show the profile page with account info
        return render_template('profile.html', account=account)
    # User is not loggedin redirect to login page
    return redirect(url_for('login'))

{% extends 'layout.html' %}

{% block title %}Profile{% endblock %}

{% block content %}
<h2>Profile Page</h2>
<div>
    <p>Your account details are below:</p>
    <table>
        <tr>
            <td>Username:</td>
            <td>{{ account['username'] }}</td>
        </tr>
        <tr>
            <td>Password:</td>
            <td>{{ account['password'] }}</td>
        </tr>
        <tr>
            <td>Email:</td>
            <td>{{ account['email'] }}</td>
        </tr>
    </table>
</div>
{% endblock %}