# File lib/mechanize/http/agent.rb, line 478
  def request_auth_digest request, uri, realm, base_uri, iis
    challenge = @digest_challenges[realm]

    uri.user = @user
    uri.password = @password

    auth = @digest_auth.auth_header uri, challenge.to_s, request.method, iis
    request['Authorization'] = auth
  end