c# - How to use TLS 1.2 in ASP.NET Core 2.0

Question

My salesforce res apis were working fine until. When suddenly I started getting authentication errors. retry your request. Salesforce.Common.AuthenticationClient.d__1.MoveNext().

salesforce informed that it would use from now TLS .1.2. How can I enforce my asp.net core 2.0 to use TLS 1.2 in Startup.cs. below is my code for login.

 private async Task<AuthenticationClient> GetValidateAuthentication()
        {
            RestApiSetting data = new RestApiSetting(Configuration);
            var auth = new AuthenticationClient();
            var url = data.IsSandBoxUser.Equals("true", StringComparison.CurrentCultureIgnoreCase)
                ? "https://test.salesforce.com/services/oauth2/token"
                : "https://login.salesforce.com/services/oauth2/token";
            try
            {
                //ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
                await auth.UsernamePasswordAsync(data.ConsumerKey,
                data.ConsumerSecret, data.Username, data.Password, url);
                return auth;
            }
            catch (Exception ex)
            {
                throw new Exception(ex.ToString());
            }
        }

Answer 1

.net framework prior to version 4.7 makes outbound connections using TLS 1.0 by default. You can upgrade to a newer version to fix the problem, or alternatively, you can set the default and fallback versions for outbound calls using the ServicePointManager, or passing the setting into the HttpClient if you have the source code for the library.

Add the following somewhere early in your pipeline, such as your startup.cs or global.asax:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

You can find a good description on the topic here: https://social.msdn.microsoft.com/Forums/en-US/8db54c83-1329-423b-8d55-4dc6a25fe826/how-to-make-a-web-client-app-use-tls-12?forum=csharpgeneral

And if you want to specify it only for some requests instead of application-wide, then you can customize the HttpClientHandler of your HttpClient:

var handler = new HttpClientHandler
{
    SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls11 | SslProtocols.Tls
};

HttpClient client = new HttpClient(handler);
...