WP function to create a shortcode to embed login form on page or post

wp-login-shortcode.php

<?php

// Use the shortcode [jay-login-form] to embed the login form

// Create shortcode
function jay_add_shortcodes() {
	add_shortcode( 'jay-login-form', 'jay_login_form_shortcode' );
}

// Shortcode callback
function jay_login_form_shortcode() {
	if ( is_user_logged_in() )
		return '<p>You are already logged in!</p>';
	return wp_login_form( array( 'echo' => false ) );
}

// Init the shortcode function
add_action( 'init', 'jay_add_shortcodes' );