With your patience, the example at: https://www.arduino.cc/en/Tutorial/Wifi101WiFiWebClientRepeating was supposed to show a 'working' example of a POST, not a failure.
A 301 response code is not a failure!
Yes, I understand 're-directs' are a fact of life, and the 301 may be the correct web response, but I still need a working set of examples of the MKR1000 and Arduino libraries that can POST, GET, and more. Have yet to see this MKR1000 and libraries function.
What is not working there? Change to URL to one of your servers and implement a correct server part to have a backend for your POST calls. POST calls usually change something on the server and I understand that the Arduino people doesn't want an example runner to change their server content.
Am I supposed to fix the library, fix the Arduino website, or fix the tutorial?
None of them, fix your expectations.