public class HttpRequest
    {
        public void MakeReqeust()
        {
            try
            {
                using (var client = new HttpClient())
                {
                    string baseUrl = ConfigurationManager.AppSettings[CommonConstants.C4ProductSubstitution.BaseUrl];
                    string getTokenEndpointUrl = string.Format("{0}/{1}", baseUrl, CommonConstants.C4ProductSubstitution.TokenUrl);
                    var formData = new Dictionary<string, string>
                    {
                        {
                            CommonConstants.C4ProductSubstitution.UsernameKey,
                            ConfigurationManager.AppSettings[CommonConstants.C4ProductSubstitution.Username].ToString()
                        },
                        {
                            CommonConstants.C4ProductSubstitution.PasswordKey,
                            ConfigurationManager.AppSettings[CommonConstants.C4ProductSubstitution.Password].ToString()
                        },
                        {
                            CommonConstants.C4ProductSubstitution.GrantTypeKey,
                            ConfigurationManager.AppSettings[CommonConstants.C4ProductSubstitution.GrantType].ToString()
                        }
                    };
                    var content = new FormUrlEncodedContent(formData);
                    ServicePointManager.SecurityProtocol |= SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
                    var result = client.PostAsync(getTokenEndpointUrl, content).GetAwaiter().GetResult();

                    if (result.StatusCode == System.Net.HttpStatusCode.OK)
                    {
                        var tokenData = result.Content.ReadAsStringAsync().Result;
                        var json = JObject.Parse(tokenData);
                        var token = json[CommonConstants.C4ProductSubstitution.TokenKey].ToString();
                        Console.WriteLine(token);
                    }
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }
        }
    }

    public class CommonConstants
    {
        public static class C4ProductSubstitution
        {
            public static readonly string BaseUrl = "C4ProductsSubstituteUrl";
            public static readonly string TokenUrl = "token";
            public static readonly string Username = "C4ProductsSubstituteUsername";
            public static readonly string UsernameKey = "username";
            public static readonly string Password = "C4ProductsSubstitutePassword";
            public static readonly string PasswordKey = "password";
            public static readonly string GrantType = "C4ProductsSubstituteGrantType";
            public static readonly string GrantTypeKey = "grant_type";
            public static readonly string AuthorizationKey = "Authorization";
            public static readonly string ProductIdKey = "Code";
            public static readonly string TokenKey = "access_token";
        }
    }