Fabulous MSAL (Microsoft Authentication Library)

Example Fabulous app that uses MSAL to authenticate a user on Azure Active Directory.

NOTE: At the time I wrote this Microsoft.Identity.Client 2.7.0 was all that was available. It is now up to 4. and has had substantial changes to the API. I will revisit this in the coming months, but the changes are substantial.

Feedback is welcome.

When I first started trying to use MSAL it was working great for WPF (not sure why), but failing on Android/UWP: from investigating more it was down to blocking on the UI thread by using Async.RunSynchronously. Typically when waiting for a task to return I would write something like:

let authResult =
    AcquireTokenAsync(...)
    |> Async.AwaitTask
    |> Async.RunSynchronously

However the issue with this is the UI thread can't be blocked to allow MSAL to open the required login windows. Thanks to this excellent article by Tomas Petricek I could solve the problem by using Async.StartChild in combination with Cmd.ofAsyncMsg.

This was a good learning experience as the MSAL examples are all in C# using await, but await behaves differently to Async.RunSynchronously in that it is non blocking: '...An await expression does not block the thread on which it is executing...'

FSharp.Azure.MSAL

This project wraps the MSAL library and returns a DU of SignInStatus which you can then call the two members SignInStatus.SignIn to authenticate a user or SignInStatus.SignOut to sign them out (on all platforms the sign in info can be cached so they will usually stay logged in even on closing the app). To create an instance of SignInStatus use SignInStatus.create which requires you to tell it what ApplicationPlatform you are using, a ClientId, a TenantId and some scopes.

Despite only been a single file this is a separate project as I plan to use it in other projects I am working on.

Setup

In the shared project MSAL.Fabulous you will need to set a ClientId, TenantId and some scopes:

let clientId = ClientId "Enter_the_Application_Id_here"
let tenantId = TenantId "Enter_the_Tenant_Info_Here"
let scopes = ["insert your scopes here"]

To get a ClientId register your app on Azure, TenantId can be found in the registered app overview. Some info on scopes, but to get started you can just pass in [""].

Android

Tested and working

iOS

I don't have access to a Mac so I haven't been able to complete the iOS project - I've gone as far as possible following the guide. Please feel free to finish it off.

UWP

The UWP app is C# - I don't believe there is another way?

WPF

This project is set to an output type of Console Application (rather than Windows Application) so that a console window appears for all the logs.

For WPF if you want to persist login info you need to implement a local storage cache. The DU case ApplicationPlatfrom.WPF requires you to choose the WPF Caching option:

| Default // Will create and use a cache in a .msalcache.bin file in the executing assembly folder
| NoCache // No caching
| CustomLocation of FileInfo // Pass in a custom file where to store the cache
| Custom of TokenCache // Pass your own cache e.g. if you were to use a database etc.

Exceptions

I'm new to Xamarin.Forms but it seems that it's not possible to catch non UI thread exceptions in the shared project, but rather it has to be implemented on the platform specific projects. MSAL will throw outside of the UI thread if the login window is closed/cancelled etc.