I've got several sites: example.com, example1.com, and example2.com in my wordpress. All of them point to my server's /public_html folder, which is my Apache root folder.  What do I need to add to my .htaccess file to use http authentication only if the user is coming from example2.com/public_html?example.com/public_html and example1.com/public_html should NOT use authentication. 
Apache authentication mutiple domain but same subdirectory
apache httpd;authentication;wordpress