class WEBrick::HTTPAuth::DigestAuth

def generate_opaque(req)
  @mutex.synchronize{
    now = req.request_time
    if now - @last_nonce_expire > @nonce_expire_delta
      @opaques.delete_if{|key,val|
        (now - val.time) > @nonce_expire_period
      }
      @last_nonce_expire = now
    end
    begin
      opaque = Utils::random_string(16)
    end while @opaques[opaque]
    @opaques[opaque] = OpaqueInfo.new(now, nil, '00000001')
    opaque
  }
end