[SOLVED] How to debug "the given key was not present in the dictionary" when authenticating through webview with Azure and Xamarin

How to debug "the given key was not present in the dictionary" when authenticating through webview with Azure and Xamarin

I am trying to get server managed authentication working with Visual Studio Mobile Center. It uses Azure App Service Authentication. I was able to setup my Facebook Developer account to allow login, then configured it on Mobile Center, and when I go to the mobile center link for auth in a web browser, it works great.

I setup the client side of the authentication identically to Adrian Hall's examples in his book: https://adrianhall.github.io/develop-mobile-apps-with-csharp-and-azure/chapter2/social/#adding-authentication-to-a-mobile-client

When the webview pops up for facebook, it lets me enter credentials, but then crashes when I hit the submit button. This is the stack trace from the application output window:

System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
[AndroidRuntime]   at System.ThrowHelper.ThrowKeyNotFoundException () [0x00000] in <8c304e4006094a46a7950338a3b3cb5d>:0 
[AndroidRuntime]   at System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) [0x00021] in <8c304e4006094a46a7950338a3b3cb5d>:0 
[AndroidRuntime]   at Microsoft.WindowsAzure.MobileServices.MobileServiceUIAuthentication+<>c__DisplayClass2_0.<LoginAsyncOverride>b__1 (System.Object sender, Xamarin.Auth._MobileServices.AuthenticatorCompletedEventArgs e) [0x00030] in <fe9883f628724025a38f5e1946e5b4c5>:0 
[AndroidRuntime]   at (wrapper delegate-invoke) System.EventHandler`1[Xamarin.Auth._MobileServices.AuthenticatorCompletedEventArgs]:invoke_void_object_TEventArgs (object,Xamarin.Auth._MobileServices.AuthenticatorCompletedEventArgs)
[AndroidRuntime]   at Xamarin.Auth._MobileServices.Authenticator+<>c__DisplayClass22_0.<OnSucceeded>b__0 () [0x00021] in <fe9883f628724025a38f5e1946e5b4c5>:0 
[AndroidRuntime]   at Java.Lang.Thread+RunnableImplementor.Run () [0x0000b] in <a4e9508b230b49a18f145a67e12eb7b8>:0 
[AndroidRuntime]   at Java.Lang.IRunnableInvoker.n_Run (System.IntPtr jnienv, System.IntPtr native__this) [0x00009] in <a4e9508b230b49a18f145a67e12eb7b8>:0 
[AndroidRuntime]   at (wrapper dynamic-method) System.Object:23f66101-d05c-44cc-a8fe-d50bbc9e59d1 (intptr,intptr)

Tested on latest Xamarin Studio and Visual Studio 2017, using Xamarin.Forms 2.3.3, latest Xamarin.Auth, and latest Azure MobileServicesClient.

Any suggestions on how to debug this? I have break on all exceptions checked and I get an Unhandled Exception with a message of "The given key was not present in the dictionary.", no inner exception or stack trace, then it crashes.

EDIT: Reproduction: https://github.com/brandonrisell/TapFriends

Solution

Open the Azure Portal
Find the resource group for your Mobile Center backend
Open up the Mobile Apps resource
Select Authentication / Authorization
Check that the Token store is turned on.

If it isn't, turn it on, save then restart and recheck.

I think that's the problem. If not, get back to me here and we'll try something else.