Blazor WASM Net 6 Preview 4 Azure AD - There was an error trying to log you in: 'Cannot read property 'toLowerCase' of undefined'

I have a simple Blazor WASM running Net 6 Preview 4 that I setup using this guide:

https://docs.microsoft.com/en-us/aspnet/core/blazor/security/webassembly/hosted-with-azure-active-directory?view=aspnetcore-6.0

The exact code works perfect with Net 5.0 (using corresponding Net 5.0 assemblies)

However when I upgrade to Net 6 I receive the following Authentication error:

There was an error trying to log you in: 'Cannot read property 'toLowerCase' of undefined'

I can’t seem to get anymore detail either. This is published on Azure App Service Self Contained publish.

The code can be found here: https://github.com/aherrick/BlazorWASM.Net6Prev4.AzureAD

[crbrz]

The issue is caused by assembly trimming done in published version (the property LoginMode in MsalProviderOptions gets removed).

To workaround it exclude Microsoft.Authentication.WebAssembly.Msal from trimming by adding this to the client project file (tester.Client.csproj):

  <ItemGroup>
    <TrimmerRootAssembly Include="Microsoft.Authentication.WebAssembly.Msal" />
  </ItemGroup>

[stephajn]

I was having this problem as well on .NET 6.0.1 using the latest version of the MSAL library. The only problem was that I wasn’t even getting any kind of error message. I would only get an empty string. Adding in the TrimRootAssembly node in my project files resolved this issue for me in multiple projects.

This issue has been open since June of 2021 and as of this writing it is February 2022. Does this mean that everyone who runs .NET 6 Blazor WASM and tries to do a Release build is having this problem? Shouldn’t something like this have been fixed before .NET 6 went to RTM? Even more so, shouldn’t it have been prioritized for the 6.0.1 release?

Or will this become part of the standard project file template if you decide to use MSAL when creating a new project?