Using MSAL.NET in Unity iOS gives PlatformNotSupportedException

[rafek]

I'm on Unity 6 and using Microsoft.Identity.Client at 4.69.1. I'm trying to implement authentication against my already configured Azure AD B2C.

My MSAL client configuration looks like this:

_msalClient =
    PublicClientApplicationBuilder
        .Create(ClientId)
        .WithB2CAuthority(Authority)
        .WithRedirectUri(RedirectUri)
        .WithIosKeychainSecurityGroup("com.my.bundle")
        .Build();

Then I perform token acquisition:

authResult = await
    _msalClient
        .AcquireTokenInteractive(Scopes)
        .WithParentActivityOrWindow(null)
        .ExecuteAsync();

I have URLTypes configured as well. What I keep getting is:

MSAL Error True True MSAL 4.69.1.0 MSAL.CoreCLR Mono Unity IL2CPP (Jan 11 2025 12:24:23) Unix 24.3.0.0 [2025-03-15 09:53:50Z - fb26809c-3bff-4bc1-85e5-cc4af6681276] System.PlatformNotSupportedException: Unix 24.3.0.0

Apparently, Unity reports the system as Unix (24.3.0.0) and it's not supported by MSAL.NET.

Is that an expected behaviour and shall I fall back to call native MSAL for iOS?

[github-actions]

Here are some similar issues that might help you. Please check if they can solve your problem.

• [Bug] System.PlatformNotSupportedException when using AcquireTokenInteractive on macOS (Darwin 23.4.0, ARM64, M3 chip) #4890
• [Bug] PlatformNotSupportedException in AcquireTokenInteractive call #1918

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Possible solution (Extracted from existing issue, might be incorrect; please verify carefully)

Solution 1:

For mobile platforms and UWP, MSAL takes care of the token cache for you. On iOS, it stores it in KeyChain. On other runtimes, developers need to define where the cache is stored. Refer to the MSAL documentation for token cache serialization on mobile.

Reference:

• [Bug] PlatformNotSupportedException in AcquireTokenInteractive call #1918 (comment)

Solution 2:

If you are using a .NET Standard assembly, ensure you add a reference to Microsoft.Identity.Client.dll from each platform assembly (e.g., UWP, Android, iOS), not just from the common .NET Standard assembly.

Reference:

• [Bug] PlatformNotSupportedException in AcquireTokenInteractive call #1918 (comment)

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