Login to WordPress Using Email Instead of Username Easily

Code

<?php
// Allow users to log in using their email address instead of username

// Hook into the 'authenticate' filter to modify the login process
add_filter('authenticate', 'wp_dudecom_allow_email_login', 20, 3);

/**
 * Allow login with email address.
 *
 * @param WP_User|WP_Error|null $user     The authenticated user object, or WP_Error or null if not authenticated.
 * @param string                $username The username or email address.
 * @param string                $password The password.
 * @return WP_User|WP_Error|null The authenticated user object, or WP_Error or null if not authenticated.
 */
function wp_dudecom_allow_email_login($user, $username, $password) {
    // Check if the username is an email address
    if (is_email($username)) {
        // Attempt to retrieve the user by email
        $user = get_user_by('email', $username);

        // If a user is found, authenticate using the found user's login
        if ($user) {
            $username = $user->user_login;
        }
    }

    // Return the result of the default authentication process
    return wp_authenticate_username_password(null, $username, $password);
}

// Hook into 'login_form' to modify the login form
add_action('login_form', 'wp_dudecom_modify_login_form');

/**
 * Modify the login form to use email address instead of username.
 */
function wp_dudecom_modify_login_form() {
    ?>
    <script type="text/javascript">
        document.addEventListener('DOMContentLoaded', function() {
            var loginLabel = document.querySelector('label[for="user_login"]');
            if (loginLabel) {
                loginLabel.textContent = 'Email Address';
            }
        });
    </script>
    <?php
}
?>