class WEBrick::HTTPAuth::DigestAuth

def challenge(req, res, stale=false)
  nonce = generate_next_nonce(req)
  if @use_opaque
    opaque = generate_opaque(req)
    @opaques[opaque].nonce = nonce
  end
  param = Hash.new
  param["realm"]  = HTTPUtils::quote(@realm)
  param["domain"] = HTTPUtils::quote(@domain.to_a.join(" ")) if @domain
  param["nonce"]  = HTTPUtils::quote(nonce)
  param["opaque"] = HTTPUtils::quote(opaque) if opaque
  param["stale"]  = stale.to_s
  param["algorithm"] = @algorithm
  param["qop"]    = HTTPUtils::quote(@qop.to_a.join(",")) if @qop
  res[@response_field] =
    "#{@auth_scheme} " + param.map{|k,v| "#{k}=#{v}" }.join(", ")
  info("%s: %s", @response_field, res[@response_field]) if $DEBUG
  raise @auth_exception
end