PHP - Implementing All Types Of Authentication in PHP

1. Basic Authentication:

// Validate user credentials
$validUsers = [
    'username1' => 'password1',
    'username2' => 'password2'
];
if (!isset($_SERVER['PHP_AUTH_USER']) || !isset($_SERVER['PHP_AUTH_PW']) ||
    !array_key_exists($_SERVER['PHP_AUTH_USER'], $validUsers) ||
    $validUsers[$_SERVER['PHP_AUTH_USER']] !== $_SERVER['PHP_AUTH_PW']) {
    header('WWW-Authenticate: Basic realm="My Protected Area"');
    header('HTTP/1.0 401 Unauthorized');
    echo 'Authentication required.';
    exit;
}
echo 'Welcome, ' . $_SERVER['PHP_AUTH_USER'] . '!';

2. Bearer Token Authentication:

$expectedToken = 'your_token_here';
$token = $_SERVER['HTTP_AUTHORIZATION'] ?? '';
if ($token !== 'Bearer ' . $expectedToken) {
    header('HTTP/1.0 401 Unauthorized');
    echo 'Authentication failed.';
    exit;
}
echo 'Authenticated!';

3. OAuth and OpenID Connect:

For OAuth and OpenID Connect, consider using established libraries like oauth2-server-php or league/oauth2-server.

4. Form-Based Authentication:

// HTML form
<form method="post" action="">
<input type="text" name="username" placeholder="Username">
<input type="password" name="password" placeholder="Password">
<button type="submit">Log In</button>
</form>
// PHP authentication
if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = $_POST['username'];
    $password = $_POST['password'];
    // Validate credentials
    if ($validUsers[$username] === $password) {
        // Successful authentication
    } else {
        // Authentication failed
    }
}

5. Windows Integrated Authentication:

This authentication method often requires server-side configuration and might involve integrating with Active Directory.

6. Digest Authentication:

Implementing Digest Authentication involves complex challenge-response mechanisms and hashing. Libraries can help with this, or you can follow RFC 7616 for detailed implementation.

Remember that proper authentication should include considerations for security, such as storing passwords securely, handling failed authentication attempts, and preventing brute-force attacks. When implementing authentication in a real-world scenario, it's recommended to use established libraries and frameworks to ensure the highest level of security and compliance.