var client = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Post, "https://id.nes.com.tr/connect/token");
var collection = new List<KeyValuePair<string, string>>();
collection.Add(new("grant_type", "password"));
collection.Add(new("username", "KULLANICI_ADI"));
collection.Add(new("password", "PAROLA"));
collection.Add(new("client_id", "mobile-app"));
collection.Add(new("scope", "openid profile roles IdentityServerApi"));
var content = new FormUrlEncodedContent(collection);
request.Content = content;
var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
Console.WriteLine(await response.Content.ReadAsStringAsync());