jwtmiddleware.go
func (m *JWTMiddleware) HandlerWithNext(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
	err := m.CheckJWT(w, r)

	// If there was an error, do not call next.
	if err == nil && next != nil {
		next(w, r)
	}
}
func (m *JWTMiddleware) HandlerWithNext(w http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
	err := m.CheckJWT(w, r)

	// If there was an error, do not call next.
	if err == nil && next != nil {
		next(w, r)
	}
}
// Special implementation for Negroni, but could be used elsewhere.