Getting ArcGIS Online token through C#

Question

I'm trying to get a token for ArcGIS Online using C# (well, more specifically SSIS). I've got a URL I can use which works well, and I can hit it and get what I need in Chrome, but it won't work through C# using a WebClient.

I can get other JSONs through it through SSIS/C# WebClient, but NOT ArcGIS Online for some reason. The URL works through Chrome, but won't yield an answer through SSIS/C# WebClient.

My code (with client id/secret/credentials) is:

string webResource = "https://mymaps.maps.arcgis.com/sharing/rest/oauth2/token?client_id=MYCLIENTID&client_secret=MYCLIENTSECRET&grant_type=client_credentials";
WebClient wc = new WebClient();
string json = wc.DownloadString(webResource);

I would then parse the JSON.

Currently I'm getting:

DTS Script Task has encountered an exception in user code:
project name: ST_0a306cf2e1634509bea49b75b7d93265
Exception has been thrown by the target of an invocation.
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
   at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)
   at Microsoft.SqlServer.Dts.Tasks.ScriptTask.VSTATaskScriptingEngine.ExecuteScript()

I have created an application, as described in https://developers.arcgis.com/labs/rest/get-an-access-token/

An example of the returned JSON (through Chrome) is:

{"access_token":"blahblahblahcrazywords..","expires_in":7200}

Answer 1

Right then, this was three things combined.

As @Vince pointed out, it needed to be a POST, not a GET.

Also, limitations of using C# in an SSIS script task, and my lack of experience.

Also, Esri expects the URLs to be using security when from an application.

As such, I needed to use this asynchronously, and encode it differently:

public void Main()
{
    Dts.Variables["User::Token"].Value = GetToken().GetAwaiter().GetResult();
}

static async Task<string> GetToken()
        {
            try
            {
                var client = new System.Net.Http.HttpClient();
                HttpContent content = new FormUrlEncodedContent(new[]
                {
                    new KeyValuePair<string, string>("client_id", "ValueHere"),
                    new KeyValuePair<string, string>("client_secret", "ValueHere"),
                    new KeyValuePair<string, string>("grant_type", "client_credentials")
                });
                ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
                var response = await client.PostAsync("https://blahblahblah.maps.arcgis.com/sharing/rest/oauth2/token", content);
                var responseString = await response.Content.ReadAsStringAsync();
                return responseString;
            }
            catch (Exception exception)
            {
                return exception.ToString();
            }
        }