Using latest NetCore Splunk.Client,
The following fails
   ServicePointManager.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) =>
        {
            return true;
        };
        Service service = new Service(new Uri(SplunkBaseUri));
        var task = service.LogOnAsync("Jas", "1234");
        task.Wait();
        return service;
With
* AuthenticationException: The remote certificate is invalid according to the validation procedure.
* HttpRequestException: The SSL connection could not be established, see inner exception.
If I write it using HttpClient, i.e.
     HttpClient client = new HttpClient(new HttpClientHandler
                {
                    ServerCertificateCustomValidationCallback = (message, certificate2, arg3, arg4) => true
                })
                {
                    BaseAddress = baseAddress
                };
This does not happen. How do we do this with the new Splunk.client?
For those who stumble onto this question from a search engine (like me), here is how I fixed this. .Net Core changed how ServicePointManager works, so instead of doing the override suggested in the Splunk docs, you need to provide a custom handler to the Context object. Like so:
var handler = new WinHttpHandler();
handler.ServerCertificateValidationCallback += (sender, certificate, chain, sslPolicyErrors) => true;
var ctx = new Context(Scheme.Https, "your_splunk_enterprise_url", 8089, default, handler);
this._splunkService = new Service(ctx);
await this._splunkService.LogOnAsync("username", "password");
After doing this the LogOnAsync method no longer returns the error about invalid certificate validation procedure etc. My app is targeting .NET Core 3.1.
Mods - can we get this added to the official documentation, perhaps?
Should probably consider using HttpClient instead WinHttp.
var handler = new HttpClientHandler
{
    ServerCertificateCustomValidationCallback =
        (sender, cert, chain, sslPolicyErrors) => { return true; }
};