private string RetrieveAccessToken(string authorizationCode)
{
var appId = GetAppId();
var appSecret = GetAppSecret();
var returnUriValue = BuildCallbackUriValue();
var param = new NameValueCollection {
{ "client_id", appId },
{ "client_secret", appSecret },
{ "code", authorizationCode },
{ "grant_type", "authorization_code" },
{ "redirect_uri", returnUriValue },
};
var url = OAuthHelpers.BuildUri(OAuthUrl, "o/oauth2/token", new NameValueCollection());
string accessToken = OAuthHelpers.GetObjectWithPost(url, param).access_token;
return(accessToken);
}