title: How to use PageSpeed in a test environment? (password protected)
body: <p>Google's PageSpeed do not run in a test environment of a website (ProdPreview). 
  I guess it's due to the password protection in it.
  Is it possible to make PageSpeed run in this environment?
  If yes, how to?</p>
  
  <p>PageSpeed give me back the message below, when I try to run it in the ProdPreview environment:</p>
  
  <p>"Lighthouse returned error: ERRORED_DOCUMENT_REQUEST. Lighthouse did not reliably load the requested page. Make sure you are testing the correct URL and that the server is responding appropriately to all requests. (Status Code: 401) Dispensing"</p>
  
  <p>No code at all.
  It's just a public tool being used in a private environment.</p>
  
  <p>Expected result:  Get the PageSpeed analysis result.
  Actual result: As described in "#2 = Provide background including what you've already tried"</p>