title: Is the client allowed to choose challenge (nonce) in Digest HTTP authentication?
body: <p>Digest authentication looks like a flavor of challenge-response mechanism: theres's a random string which is mixed with the password (MD5 or something) by both the client and the server and only the result of such mixing is sent over the network.</p>
  
  <p>Usually the challenge ("nonce") is chosen by the server and sent to the client. <a href="http://en.wikipedia.org/wiki/Digest_access_authentication" rel="nofollow">Wikipedia article</a> on digest authentication lists a sample "session" - the challenge ("nonce") is chosen by the server there. I tested the same with IIS on my machine - again, the challenge is generated by IIS.</p>
  
  <p>But in some posts <a href="https://developer.omniture.com/node/4237" rel="nofollow">like this one</a> the challenge is generated by the client - the client just generates a random string and sends a request with the challenge and the product of the password and that challenge.</p>
  
  <p>Is the latter allowed and widely accepted? Is the client allowed to choose the challenge ("nonce")?</p>