How to get a facebook access token using appid and app secre

Question

I need to get FaceBook user access token using appid and app secret in C# windows application without any Facebook login pop up window. Actually i did below coding, but getting app token only,not getting the user access token. how to get user access token to post in a FB Wall.?

The Graph API Explorer (https://developers.facebook.com/tools/explorer) generates an access token which is typically 118 characters in length, whereas the token returned is far less.

FacebookClient client = new FacebookClient();
dynamic result = client.Get("oauth/access_token", new
{
client_id = "XXXXXXXXXXXXXXX",
client_secret = "XXXXXXXXXXXXXXXXXXX",
grant_type = "client_credentials"
});
var accessToken = result.access_token;

Help me to proceed further..