Is there any other way to monitor url's other than using the url_response probe ?
e2e_appmon
There is the e2e_appmon transaction scripting probe which can look for text on a page, click buttons, etc... and report response time, failures, qos, etc...
E2E Application Response
net_connect
There is also the net_connect probe which can test whether a service is listening on port 80/443:
net_connect
logmon
Another option is the logmon probe in combination with a shell script or batch file run using command mode.
That script/batch file could call the OS curl command to fetch a URL and report on the response or HTTP status, etc...
url_response endpoint response monitoring
Treating a 401 error as valid is not supported by the url_response probe.
Even if the given URL which requires authentication is 'accessible,' it does not guarantee that the target page is available. Therefore, it will be incorrect to report a URL as 'available' if a 401 error is received.
The best option is to ask the customer to provide a username and perhaps a complex password that they are comfortable with so that they can be configured in the probe for Windows NT authentication (since that is what is being used by the website).