PHP MySQL 登录系统

In this tutorial you will learn how to build a login system with PHP and MySQL.

## Implementing User Authentication Mechanism
User authentication is very common in modern web application. It is a security mechanism that is used to restrict unauthorized access to member-only areas and tools on a site.

In this tutorial we'll create a simple registration and login system using the PHP and MySQL. This tutorial is comprised of two parts: in the first part we'll create a user registration form, and in the second part we'll create a login form, as well as a welcome page and a logout script.

## Building the Registration System
In this section we'll build a registration system that allows users to create a new account by filling out a web form. But, first we need to create a table that will hold all the user data.

### Step 1: Creating the Database Table
Execute the following SQL query to create the users table inside your MySQL database.

```sql
CREATE TABLE users (
    id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(50) NOT NULL UNIQUE,
    password VARCHAR(255) NOT NULL,
    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);
```
Please check out the tutorial on [SQL CREATE TABLE](http://www.bixiaguangnian.com/manual/sql/3390.html "SQL CREATE TABLE") statement for the detailed information about syntax for creating tables in MySQL database system.

### Step 2: Creating the Config File
After creating the table, we need create a PHP script in order to connect to the MySQL database server. Let's create a file named "config.php" and put the following code inside it.

```php
<?php
/* Database credentials. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
define('DB_SERVER', 'localhost');
define('DB_USERNAME', 'root');
define('DB_PASSWORD', '');
define('DB_NAME', 'demo');
 
/* Attempt to connect to MySQL database */
$link = mysqli_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD, DB_NAME);
 
// Check connection
if($link === false){
    die("ERROR: Could not connect. " . mysqli_connect_error());
}
?>
```

If you've downloaded the Object Oriented or PDO code examples using the download button, please remove the text "-oo-format" or "-pdo-format" from file names before testing the code.

<div class="callout callout-info mb-3">Note: Replace the credentials according to your MySQL server setting before testing this code, for example, replace the database name 'demo' with your own database name, replace username 'root' with your own database username, specify database password if there's any.</div>

### Step 3: Creating the Registration Form
Let's create another PHP file "register.php" and put the following example code in it. This example code will create a web form that allows user to register themselves.

This script will also generate errors if a user tries to submit the form without entering any value, or if username entered by the user is already taken by another user.

```php
<?php
// Include config file
require_once "config.php";
 
// Define variables and initialize with empty values
$username = $password = $confirm_password = "";
$username_err = $password_err = $confirm_password_err = "";
 
// Processing form data when form is submitted
if($_SERVER["REQUEST_METHOD"] == "POST"){
 
    // Validate username
    if(empty(trim($_POST["username"]))){
        $username_err = "Please enter a username.";
    } elseif(!preg_match('/^[a-zA-Z0-9_]+$/', trim($_POST["username"]))){
        $username_err = "Username can only contain letters, numbers, and underscores.";
    } else{
        // Prepare a select statement
        $sql = "SELECT id FROM users WHERE username = ?";
        
        if($stmt = mysqli_prepare($link, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "s", $param_username);
            
            // Set parameters
            $param_username = trim($_POST["username"]);
            
            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                /* store result */
                mysqli_stmt_store_result($stmt);
                
                if(mysqli_stmt_num_rows($stmt) == 1){
                    $username_err = "This username is already taken.";
                } else{
                    $username = trim($_POST["username"]);
                }
            } else{
                echo "Oops! Something went wrong. Please try again later.";
            }

// Close statement
            mysqli_stmt_close($stmt);
        }
    }
    
    // Validate password
    if(empty(trim($_POST["password"]))){
        $password_err = "Please enter a password.";     
    } elseif(strlen(trim($_POST["password"])) < 6){
        $password_err = "Password must have atleast 6 characters.";
    } else{
        $password = trim($_POST["password"]);
    }
    
    // Validate confirm password
    if(empty(trim($_POST["confirm_password"]))){
        $confirm_password_err = "Please confirm password.";     
    } else{
        $confirm_password = trim($_POST["confirm_password"]);
        if(empty($password_err) && ($password != $confirm_password)){
            $confirm_password_err = "Password did not match.";
        }
    }
    
    // Check input errors before inserting in database
    if(empty($username_err) && empty($password_err) && empty($confirm_password_err)){
        
        // Prepare an insert statement
        $sql = "INSERT INTO users (username, password) VALUES (?, ?)";
         
        if($stmt = mysqli_prepare($link, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "ss", $param_username, $param_password);
            
            // Set parameters
            $param_username = $username;
            $param_password = password_hash($password, PASSWORD_DEFAULT); // Creates a password hash
            
            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                // Redirect to login page
                header("location: login.php");
            } else{
                echo "Oops! Something went wrong. Please try again later.";
            }

// Close statement
            mysqli_stmt_close($stmt);
        }
    }
    
    // Close connection
    mysqli_close($link);
}
?>
 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Sign Up</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
    <style>
        body{ font: 14px sans-serif; }
        .wrapper{ width: 360px; padding: 20px; }
    </style>
</head>
<body>
    <div class="wrapper">
        <h2>Sign Up</h2>
        <p>Please fill this form to create an account.</p>
        <form action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>" method="post">
            <div class="form-group">
                <label>Username</label>
                <input type="text" name="username" class="form-control <?php echo (!empty($username_err)) ? 'is-invalid' : ''; ?>" value="<?php echo $username; ?>">
                <span class="invalid-feedback"><?php echo $username_err; ?></span>
            </div>    
            <div class="form-group">
                <label>Password</label>
                <input type="password" name="password" class="form-control <?php echo (!empty($password_err)) ? 'is-invalid' : ''; ?>" value="<?php echo $password; ?>">
                <span class="invalid-feedback"><?php echo $password_err; ?></span>
            </div>
            <div class="form-group">
                <label>Confirm Password</label>
                <input type="password" name="confirm_password" class="form-control <?php echo (!empty($confirm_password_err)) ? 'is-invalid' : ''; ?>" value="<?php echo $confirm_password; ?>">
                <span class="invalid-feedback"><?php echo $confirm_password_err; ?></span>
            </div>
            <div class="form-group">
                <input type="submit" class="btn btn-primary" value="Submit">
                <input type="reset" class="btn btn-secondary ml-2" value="Reset">
            </div>
            <p>Already have an account? <a href="login.php">Login here</a>.</p>
        </form>
    </div>    
</body>
</html>
```

— The output of the above example (i.e. signup form) will look something like this:

![PHP MySQL Sign Up Form](/uploads/images/20240507/a7d346e27b5cf88e6298969a4bca7260.png "PHP MySQL Sign Up Form")

In the above example, we have used the PHP's inbuilt `password_hash()` function to create a password hash from the password string entered by the user (line no-78). This function creates a password hash using a strong one-way hashing algorithm. It also generates and applies a random salt automatically when hashing the password; this basically means that even if two users have the same passwords, their password hashes will be different.

At the time of login we'll verify the given password with the password hash stored in the database using the PHP `password_verify()` function, as demonstrated in the next example.

We've used the Bootstrap framework to make the form layouts quickly and beautifully. Please, checkout the Bootstrap tutorial section to learn more about this framework.

<div class="callout callout-success mb-3">Tip: Password salting is a technique which is widely used to secure passwords by randomizing password hashes, so that if two users have the same password, they will not have the same password hashes. This is done by appending or prepending a random string, called a salt, to the password before hashing.</div>

## Building the Login System
In this section we'll create a login form where user can enter their username and password. When user submit the form these inputs will be verified against the credentials stored in the database, if the username and password match, the user is authorized and granted access to the site, otherwise the login attempt will be rejected.

### Step 1: Creating the Login Form
Let's create a file named "login.php" and place the following code inside it.

```php
<?php
// Initialize the session
session_start();
 
// Check if the user is already logged in, if yes then redirect him to welcome page
if(isset($_SESSION["loggedin"]) && $_SESSION["loggedin"] === true){
    header("location: welcome.php");
    exit;
}
 
// Include config file
require_once "config.php";
 
// Define variables and initialize with empty values
$username = $password = "";
$username_err = $password_err = $login_err = "";
 
// Processing form data when form is submitted
if($_SERVER["REQUEST_METHOD"] == "POST"){
 
    // Check if username is empty
    if(empty(trim($_POST["username"]))){
        $username_err = "Please enter username.";
    } else{
        $username = trim($_POST["username"]);
    }
    
    // Check if password is empty
    if(empty(trim($_POST["password"]))){
        $password_err = "Please enter your password.";
    } else{
        $password = trim($_POST["password"]);
    }
    
    // Validate credentials
    if(empty($username_err) && empty($password_err)){
        // Prepare a select statement
        $sql = "SELECT id, username, password FROM users WHERE username = ?";
        
        if($stmt = mysqli_prepare($link, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "s", $param_username);
            
            // Set parameters
            $param_username = $username;
            
            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                // Store result
                mysqli_stmt_store_result($stmt);
                
                // Check if username exists, if yes then verify password
                if(mysqli_stmt_num_rows($stmt) == 1){                    
                    // Bind result variables
                    mysqli_stmt_bind_result($stmt, $id, $username, $hashed_password);
                    if(mysqli_stmt_fetch($stmt)){
                        if(password_verify($password, $hashed_password)){
                            // Password is correct, so start a new session
                            session_start();
                            
                            // Store data in session variables
                            $_SESSION["loggedin"] = true;
                            $_SESSION["id"] = $id;
                            $_SESSION["username"] = $username;                            
                            
                            // Redirect user to welcome page
                            header("location: welcome.php");
                        } else{
                            // Password is not valid, display a generic error message
                            $login_err = "Invalid username or password.";
                        }
                    }
                } else{
                    // Username doesn't exist, display a generic error message
                    $login_err = "Invalid username or password.";
                }
            } else{
                echo "Oops! Something went wrong. Please try again later.";
            }

// Close statement
            mysqli_stmt_close($stmt);
        }
    }
    
    // Close connection
    mysqli_close($link);
}
?>
 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Login</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
    <style>
        body{ font: 14px sans-serif; }
        .wrapper{ width: 360px; padding: 20px; }
    </style>
</head>
<body>
    <div class="wrapper">
        <h2>Login</h2>
        <p>Please fill in your credentials to login.</p>

<?php 
        if(!empty($login_err)){
            echo '<div class="alert alert-danger">' . $login_err . '</div>';
        }        
        ?>

<form action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>" method="post">
            <div class="form-group">
                <label>Username</label>
                <input type="text" name="username" class="form-control <?php echo (!empty($username_err)) ? 'is-invalid' : ''; ?>" value="<?php echo $username; ?>">
                <span class="invalid-feedback"><?php echo $username_err; ?></span>
            </div>    
            <div class="form-group">
                <label>Password</label>
                <input type="password" name="password" class="form-control <?php echo (!empty($password_err)) ? 'is-invalid' : ''; ?>">
                <span class="invalid-feedback"><?php echo $password_err; ?></span>
            </div>
            <div class="form-group">
                <input type="submit" class="btn btn-primary" value="Login">
            </div>
            <p>Don't have an account? <a href="register.php">Sign up now</a>.</p>
        </form>
    </div>
</body>
</html>
```

— The output of the above example (i.e. login form) will look something like this:

![PHP MySQL Sign Up Form](/uploads/images/20240507/a7d346e27b5cf88e6298969a4bca7260.png "PHP MySQL Sign Up Form")
### Step 2: Creating the Welcome Page
Here's the code of our "welcome.php" file, where user is redirected after successful login.

```php
<?php
// Initialize the session
session_start();
 
// Check if the user is logged in, if not then redirect him to login page
if(!isset($_SESSION["loggedin"]) || $_SESSION["loggedin"] !== true){
    header("location: login.php");
    exit;
}
?>
 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Welcome</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
    <style>
        body{ font: 14px sans-serif; text-align: center; }
    </style>
</head>
<body>
    <h1 class="my-5">Hi, <b><?php echo htmlspecialchars($_SESSION["username"]); ?></b>. Welcome to our site.</h1>
    <p>
        <a href="reset-password.php" class="btn btn-warning">Reset Your Password</a>
        <a href="logout.php" class="btn btn-danger ml-3">Sign Out of Your Account</a>
    </p>
</body>
</html>
```

If data comes from external sources like form filled in by anonymous users, there is a risk that it may contain malicious script indented to launch cross-site scripting (XSS) attacks. Therefore, you must escape this data using the PHP `htmlspecialchars()` function before displaying it in the browser, so that any HTML tag it contains becomes harmless.

For example, after escaping special characters the string `<script>alert("XSS")</script>` becomes `&lt;script&gt;alert("XSS")&lt;/script&gt;` which is not executed by the browser.

### Step 3: Creating the Logout Script
Now, let's create a "logout.php" file. When the user clicks on the log out or sign out link, the script inside this file destroys the session and redirect the user back to the login page.

```php
<?php
// Initialize the session
session_start();
 
// Unset all of the session variables
$_SESSION = array();
 
// Destroy the session.
session_destroy();
 
// Redirect to login page
header("location: login.php");
exit;
?>
```

## Adding the Password Reset Feature
Finally, in this section we will add the password reset utility to our login system. Using this feature logged in users can instantly reset their own password for their accounts.

Let's create a file named "reset-password.php" and place the following code inside it.

```php
<?php
// Initialize the session
session_start();
 
// Check if the user is logged in, otherwise redirect to login page
if(!isset($_SESSION["loggedin"]) || $_SESSION["loggedin"] !== true){
    header("location: login.php");
    exit;
}
 
// Include config file
require_once "config.php";
 
// Define variables and initialize with empty values
$new_password = $confirm_password = "";
$new_password_err = $confirm_password_err = "";
 
// Processing form data when form is submitted
if($_SERVER["REQUEST_METHOD"] == "POST"){
 
    // Validate new password
    if(empty(trim($_POST["new_password"]))){
        $new_password_err = "Please enter the new password.";     
    } elseif(strlen(trim($_POST["new_password"])) < 6){
        $new_password_err = "Password must have atleast 6 characters.";
    } else{
        $new_password = trim($_POST["new_password"]);
    }
    
    // Validate confirm password
    if(empty(trim($_POST["confirm_password"]))){
        $confirm_password_err = "Please confirm the password.";
    } else{
        $confirm_password = trim($_POST["confirm_password"]);
        if(empty($new_password_err) && ($new_password != $confirm_password)){
            $confirm_password_err = "Password did not match.";
        }
    }
        
    // Check input errors before updating the database
    if(empty($new_password_err) && empty($confirm_password_err)){
        // Prepare an update statement
        $sql = "UPDATE users SET password = ? WHERE id = ?";
        
        if($stmt = mysqli_prepare($link, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "si", $param_password, $param_id);
            
            // Set parameters
            $param_password = password_hash($new_password, PASSWORD_DEFAULT);
            $param_id = $_SESSION["id"];
            
            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                // Password updated successfully. Destroy the session, and redirect to login page
                session_destroy();
                header("location: login.php");
                exit();
            } else{
                echo "Oops! Something went wrong. Please try again later.";
            }

// Close statement
            mysqli_stmt_close($stmt);
        }
    }
    
    // Close connection
    mysqli_close($link);
}
?>
 
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Reset Password</title>
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css">
    <style>
        body{ font: 14px sans-serif; }
        .wrapper{ width: 360px; padding: 20px; }
    </style>
</head>
<body>
    <div class="wrapper">
        <h2>Reset Password</h2>
        <p>Please fill out this form to reset your password.</p>
        <form action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>" method="post"> 
            <div class="form-group">
                <label>New Password</label>
                <input type="password" name="new_password" class="form-control <?php echo (!empty($new_password_err)) ? 'is-invalid' : ''; ?>" value="<?php echo $new_password; ?>">
                <span class="invalid-feedback"><?php echo $new_password_err; ?></span>
            </div>
            <div class="form-group">
                <label>Confirm Password</label>
                <input type="password" name="confirm_password" class="form-control <?php echo (!empty($confirm_password_err)) ? 'is-invalid' : ''; ?>">
                <span class="invalid-feedback"><?php echo $confirm_password_err; ?></span>
            </div>
            <div class="form-group">
                <input type="submit" class="btn btn-primary" value="Submit">
                <a class="btn btn-link ml-2" href="welcome.php">Cancel</a>
            </div>
        </form>
    </div>    
</body>
</html>
```