class HTTPClient::ProxyDigestAuth

def get(req)

before
regardless of target uri if the proxy has required authentication
overrides DigestAuth#get. Uses default user name and password 
def get(req)
  synchronize {
    param = @challenge
    return nil unless param
    user, passwd = @auth
    return nil unless user
    calc_cred(req, user, passwd, param)
  }
end