I'm trying to find an explanation for a very strange behaviour.
The pice of code is quite simple:
// A simple HTTP GET call with RestSharp.
var url = "https://sandbox.tradier.com/v1/markets/quotes?symbols=MSFT";
var bearerToken = "thisCouldBeYourToken";
var client = new RestClient(url);
var request = new RestRequest(Method.GET);
request.AddHeader("Authorization", $"Bearer {bearerToken}");
var response = await client.ExecuteTaskAsync<MyClass>(request)
The code is part of a .NET 4.7.2 WPF applicaiton deployed with ClickOnce.
A couple of days ago, without any changes, this call suddenly returned An existing connection was forcibly closed by the remote host. However only for this particular URL. I use the exact same code for other URLs as well without any problems.
What was really strange, when I debugged the application the exception didn't occur, I received the desired response instead. Even when I started the application without debuggung, no error. I redeployed the app, but still the error occurred there. So for some reason the call is made differently after it was deployed!? BTW: Also the deployed version is running on my computer, not somewhere else.
After some intensive googling I came across this post, which suggested to explicitly set the SecurityProtocol to TLS 1.2 (default value: SystemDefault):
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
It worked like a charm. Now also the deployed version is running without any problems. So I guess the URL demands TLS 1.2 now, alright. But why did the app run even before when started directly and ran into problems when deployed via ClickOnce?
I've not verified it, but it seems that KB4520405 (KB4519565) changes ClickOnce application from TLS 1.2 to 1.0 .
So, via ClickOnce it started to launch by default and older TLS version.