Wordpress wp-admin goes into loop when on cloudflare ssl

If there is no ssl configured on web server but is enabled in cluodflare,wp-admin often goes in to loop with error:

The page isn’t redirecting properly

An error occurred during a connection to quality-nomads.com.

    This problem can sometimes be caused by disabling or refusing to accept cookies.

Solution is:

1. Download cert from cloudflare and install it on web server
2. Set ssl to config to "full" in cloudflare
3. Add few config directives into wp-config.php file:

define('FORCE_SSL_ADMIN', true);
// in some setups HTTP_X_FORWARDED_PROTO might contain
// a comma-separated list e.g. http,https
// so check for https existence
if (strpos($_SERVER['HTTP_X_FORWARDED_PROTO'], 'https') !== false)
       $_SERVER['HTTPS']='on';