Connection issue with TLS 1.1 and 1.2 - Azure web app

Question

In my application I am calling an API written in WebAPI and hosted in a PaaS environment in azure from another WebAPI method (ideally an internal service call), say MethodA in WebApp_A is calling MethodB in WebApp_B. But i am getting the mentioned error if the TLS settings of WebApp_B is either 1.1 or 1.2 ( it works with 1.0). "Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host."

I have similar WebApp (WebApp_C) which doesn't have the error with TLS. Below is the code that we use to call the MethodB in WebApp_B from WebApp_A

 public async Task<ServiceResponse> CreateDialog(RequestObject requestObject)
 {
        ServiceResponse serviceResponse = new ServiceResponse();
        try
        {
            using (var client = new HttpClient())
            {

                SessionTokenBo jwtData = new SessionTokenBo();
                Logger = _logger;
                jwtData = GetInternalToken(InternalCallTypes.Utilities.ToString(), int.Parse(ServiceConfiguration.TokenExpiryWindow), int.Parse(ServiceConfiguration.InternalTokenExpiryWindow));
                if (null != jwtData)
                {
                    client.BaseAddress = new Uri("URI");
                    client.DefaultRequestHeaders.Accept.Clear();
                    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                    client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", jwtData.Token);                        HttpResponseMessage response = await client.PostAsJsonAsync("service/methodB", requestObject);                        
                    if (response.IsSuccessStatusCode)
                    {
                        var data = response.Content.ReadAsStringAsync().Result;
                        serviceResponse = JsonConvert.DeserializeObject<ServiceResponse>(data);
                    }
                }
            }
        }
        catch (Exception ex)
        {
           throw
        }
        return serviceResponse;
  }

If i give Security protocol like this , it will work

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

Also i tried from postman with the request and it is not failing. So now am confused because if from postman its working then ideally its not the WebApp setup issue

Answer 1

TLS 1.0 is no longer the default. Add this line before making the request:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

Have a Reference to this issue .

Update:

but my doubt is why the same code is not failing for other web apps ?

Found the issue, it was due the target framework was 4.5.2 in webconfig.

<compilation targetFramework="4.7.2"></compilation> 
<httpRuntime targetFramework="4.7.2" />