API is returning error when using RESTSHARP

Question

When use RestSharp to call an API I get this error:

The underlying connection was closed: An unexpected error occurred on a send.

I've verified that my client ID, secret, username, and password are correct. I'm able to do this without issues in PowerShell.

public string GetTokenForBrightIdea()
{
    RestClient restclient = new RestClient(_uri);
    RestRequest request = new RestRequest() { Method = Method.POST };

    request.AddHeader("Accept", "application/json");
    request.AddHeader("Content-Type", "application/x-www-form-urlencoded");
    request.AddParameter("grant_type", "password");
    request.AddParameter("client_id", _clientId);
    request.AddParameter("client_secret", _clientSecret);
    request.AddParameter("username", _clientUsername);
    request.AddParameter("password", _clientPassword);

    var tResponse = restclient.Execute(request);
    var responseJson = tResponse.Content;
    return JsonConvert.DeserializeObject<Dictionary<string, object>>(
        responseJson)["access_token"].ToString();
}

What am I missing when using RestSharp to make this work?

Answer 1

So it turns out that because this call was HTTPS i needed to add the following line of code

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

Answer 2

For .Net 3.5 and 4.0 you could try putting this line of code prior to the initialization of the RestSharp client:

ServicePointManager.SecurityProtocol = (SecurityProtocolType)768 | (SecurityProtocolType)3072;

Answer 3

This worked fine for me:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12;