Answers for "check if user and password is correct wordpress"

if user logged in wordpress

if ( is_user_logged_in() ) {
   // your code for logged in user 
} else {
   // your code for logged out user 
}

wordpress check if page is password protected

//post id is optional
if(post_password_required($post_id)) {}
//or
if(!empty($post->post_password)){
   // do some stuff
}