generate_opaque

# File lib/webrick/httpauth/digestauth.rb, line 330
      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