Azure AD Client Credentials Grant Xamarin iOS - azure

Question

We are attempting to write an iOS app using Xamarin that authenticates with our rest api secured using azure ad. In our case, the app will be deployed onto enterprise iOS devices and will need to run for about 8 hours on a single day of the year. The app/api do not need to know the user that is signed in, therefore this application will run more as a daemon application instead of a native appliction. The code below is giving an object reference exception, which I included the stack trace of below as well. We are able to get the service authenticated when entering user credentials but this is not ideal given our deployed environment.
My question is: Is this authentication method flat out not supported by ADAL on Xamarin iOS? If so, is there another authentication library that we can use to accomplish this or are we swimming upstream by trying to do our authentication this way?
static async void LoadService()
{
try
{
string aadInstance = "https://login.microsoftonline.com/{0}";
string tenant = "ourname.onmicrosoft.com";
string clientId = "our client id";
string appKey = "our app key";
string authority = string.Format(CultureInfo.InvariantCulture, aadInstance, tenant);
string resourceId = "https://ourname.onmicrosoft.com/TheService";
AuthenticationContext authContext = new AuthenticationContext(authority);
ClientCredential clientCredential = new ClientCredential(clientId, appKey);
AuthenticationResult result = await authContext.AcquireTokenAsync(resourceId, clientCredential);
HttpClient client = new HttpClient();
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", result.AccessToken);
}
catch (Exception ex)
{
ex.ToString();
}
}
Error Stack Trace:
at Microsoft.IdentityModel.Clients.ActiveDirectory.BrokerHelper.get_CanInvokeBroker () [0x0000c] in <filename unknown>:0
at Microsoft.IdentityModel.Clients.ActiveDirectory.AcquireTokenHandlerBase+<RunAsync>d__54.MoveNext () [0x0027d] in <filename unknown>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:201
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:170
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:142
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:372
at Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext+<AcquireTokenForClientCommonAsync>d__45.MoveNext () [0x00081] in <filename unknown>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:201
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:170
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:142
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:372
at Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext+<AcquireTokenAsync>d__22.MoveNext () [0x00071] in <filename unknown>:0
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:201
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:170
at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:142
at System.Runtime.CompilerServices.TaskAwaiter`1[TResult].GetResult () [0x00000] in /Users/builder/data/lanes/3051/5f11db87/source/maccore/_build/Library/Frameworks/Xamarin.iOS.framework/Versions/git/src/mono/external/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:372
at App1.ViewController+<LoadService>d__3.MoveNext () [0x000c7] in C:\Users\brians\Documents\Visual Studio 2015\Projects\App2\App1\ViewController.cs:52