Allow Only Logged-In Users

add_action(

	'wp',

	static function () {

		if ( is_user_logged_in() ) {

			return;

		}

		// Handle API requests separately.

		if ( defined( 'REST_REQUEST' ) && REST_REQUEST ) {

			return;

		}

		// Allow access to the login screens.

		$allowed = array(

			'wp-login.php'     => true,

			'wp-signup.php'    => true,

			'wp-activate.php'  => true,

			'wp-trackback.php' => true,

			'wp-cron.php'      => true,

		);

		if ( isset( $allowed[ basename( $_SERVER['PHP_SELF'] ) ] ) ) {

			return;

		}

		nocache_headers();

		wp_safe_redirect(

			wp_login_url(

				set_url_scheme( 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] )

			)

		);

		exit;

	}

);

// Custom Login error.

add_action(

	'init',

	static function () {

		global $error;

		if ( 'wp-login.php' !== basename( $_SERVER['PHP_SELF'] ) || ! empty( $_POST ) || ( ! empty( $_GET ) && empty( $_GET['redirect_to'] ) ) ) {

			return;

		}

		$redirect = isset( $_GET['redirect_to'] ) ? $_GET['redirect_to'] : '';

		if ( ! $redirect || str_starts_with( $redirect, admin_url() ) ) {

			return;

		}

		$error = __( 'You need to login to access this website.' );

	}

);

// Force logged-in only traffic for the API.

add_filter(

	'rest_authentication_errors',

	static function ( $result ) {

		if ( is_wp_error( $result ) ) {

			return $result;

		}

		if ( ! is_user_logged_in() ) {

			return new WP_Error(

				'rest_not_logged_in',

				__( 'This content is restricted to logged-in users.' ),

				array( 'status' => 401 )

			);

		}

		return $result;

	}

);

// Don't allow indexing.

add_action( 'pre_option_blog_public', '__return_zero' );