When attempting to connect to a server through an HTTP proxy that requires Digest authentication, the proxy sends back a 407 error. The client should then use the information sent back along with the 407 to create the correct Digest Header and try the request again but it doesn't.
Instead the HTTPConduit attempts one request and then goes into the handleResponseInternal() method where it checks the response code
and throws an HTTPException instead of finishing the Digest transaction.
In the processRetransmit() method it check for a 401 error and then attempts the authorizationRetransmit() BUT it does not handle the 407 error.