PHP create USER authentication

Programming
1 
function user_auth(){
	$auth['username']='ankhbaatar';
	$auth['password']='PASSWORD_HERE';
	
			if(!isset($_SERVER['PHP_AUTH_USER'])) {
		        header("WWW-Authenticate: Basic realm=\"Private Area\"");
		        header("HTTP/1.0 401 Unauthorized");
		        exit;
		    } else { 
		        if (($_SERVER['PHP_AUTH_USER'] == $auth['username']) && ($_SERVER['PHP_AUTH_PW'] == $auth['password'])) { 

		            } 
		        	else {
		        	header("WWW-Authenticate: Basic realm=\"Private Area\"");
		            header("HTTP/1.0 401 Unauthorized");
		            //print "Sorry - you need valid credentials to be granted access!\n";
		            exit;
		        } 
		    }
		    unset($_SERVER['PHP_AUTH_USER']);	
}