Method nbf_param

include/jwt/parameters.hpp:254–257

struct nbf_param
{
  nbf_param(const jwt::system_time_t tp)
    : duration_(std::chrono::duration_cast<
        std::chrono::seconds>(tp.time_since_epoch()).count())
  {}

  nbf_param(const uint64_t epoch)
    : duration_(epoch)