How can debugging techniques be applied to troubleshoot issues with PHP login functionality, especially when transitioning from a previous project?

Issue: When transitioning from a previous project, PHP login functionality may encounter issues due to differences in database structure, session handling, or authentication logic. To troubleshoot these issues, debugging techniques such as using error reporting, logging, and step-by-step code inspection can help identify and resolve the root cause of the problem. 

<?php
// Enable error reporting to catch any PHP errors or warnings
error_reporting(E_ALL);
ini_set('display_errors', 1);

// Use logging to track the flow of the login functionality
$logFile = 'login_log.txt';
$logMessage = date('Y-m-d H:i:s') . ' - Login attempt: ' . $_POST['username'] . PHP_EOL;
file_put_contents($logFile, $logMessage, FILE_APPEND);

// Inspect the code step-by-step to identify any discrepancies in the login process
// Check database queries, session handling, and authentication logic for any issues

// Sample code for connecting to the database and querying user credentials
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

$conn = new mysqli($servername, $username, $password, $dbname);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$username = $_POST['username'];
$password = $_POST['password'];

$sql = "SELECT * FROM users WHERE username='$username' AND password='$password'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // User authenticated successfully
    session_start();
    $_SESSION['username'] = $username;
    header("Location: dashboard.php");
} else {
    // Invalid credentials
    echo "Invalid username or password";
}

$conn->close();
?>

Keywords

PHP debugging techniques login functionality troubleshooting transition.

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