func ParseWithClaims(tokenStr string, claims *MapClaims, fn func(*MapClaims) ([]byte, error)) error {
	// Key lookup function has to be provided.
	if fn == nil {
		// keyFunc was not provided, return error.
		return jwtgo.NewValidationError("no Keyfunc was provided.", jwtgo.ValidationErrorUnverifiable)
	}

	bufp := base64BufPool.Get().(*[]byte)
	defer base64BufPool.Put(bufp)

	tokenBuf := base64BufPool.Get().(*[]byte)