If you have your site footer and masthead (e.g. including main menu, hero image, etc.) HTMLs as separate template files, you could bascially include them on the default login page like this,
add_action('login_head',function(){
get_template_part( 'site-header' );
});
add_action('login_footer',function(){
get_template_part( 'footer' );
});
I wouldn’t use get_header
and get_footer
directly as they probably contain some extra opening and closing html tags (html,body..), which might cause weird results.
You’ll need to enqueue your theme styles and scripts also,
add_action( 'login_enqueue_scripts', 'theme_styles_and_scripts_enqueue_function' );
You might also want to do some extra styling to make the login form look the way you want.