What are the best practices for securely querying a database in PHP to authenticate users based on session data?

When querying a database in PHP to authenticate users based on session data, it is important to use parameterized queries to prevent SQL injection attacks. Additionally, always validate and sanitize user input before using it in a query to ensure data integrity. Lastly, consider implementing password hashing and salting techniques to securely store and compare user passwords. 

// Connect to the database
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

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

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

// Prepare a SQL statement using parameterized query
$stmt = $conn->prepare("SELECT * FROM users WHERE username = ? AND password = ?");
$stmt->bind_param("ss", $username, $password);

// Set session data
$_SESSION['username'] = $username;

// Execute the query
$stmt->execute();

// Check if user exists in the database
if ($stmt->num_rows > 0) {
    // User authenticated successfully
    echo "User authenticated successfully";
} else {
    // User authentication failed
    echo "User authentication failed";
}

// Close the statement and connection
$stmt->close();
$conn->close();

Keywords

SQL injection prepared statements password hashing session management authentication

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