code: func ExpiresIn(d time.Duration) Option {
  	return func(tok *Bearer) error {
  		if d != 0 {
  			tok.addExpiration = true
  			tok.expiresIn = d
  		} else {
  			tok.addExpiration = false
  			tok.expiresIn = 0
  		}
  
  		return nil
  	}
  }
docs: // ExpiresIn is an option that will set the expiration duration generated for
  // tokens to the specified duration.