Identity: Default Bootstrap version of UI changed

Starting in ASP.NET Core 6.0, Identity UI defaults to using version 5 of Bootstrap. ASP.NET Core 3.0 to 5.0 used version 4 of Bootstrap.

Version introduced

ASP.NET Core 6.0

Behavior

xref:Microsoft.Extensions.DependencyInjection.IdentityServiceCollectionUIExtensions.AddDefaultIdentity%60%601(Microsoft.Extensions.DependencyInjection.IServiceCollection) calls the internal private method TryResolveUIFramework. TryResolveUIFramework reads the xref:Microsoft.AspNetCore.Identity.UI.UIFramework from the application assembly. The UIFramework version defaults to:

Bootstrap 5 for the .NET 6 SDK
Bootstrap 4 for the .NET Core 3.1 and .NET 5 SDK

Template-created ASP.NET Core 3.1 and 5.0 apps contain Bootstrap 4 in wwwroot\lib\bootstrap. Template-created ASP.NET Core 6 apps use Bootstrap 5. When an ASP.NET Core 3.1 or 5.0 app is migrated to .NET 6, the application detects UIFramework version 5, while wwwroot\lib\bootstrap contains version 4. This version mismatch renders the Identity templates incorrectly.

Reason for change

Bootstrap 5 was released during the ASP.NET Core 6.0 timeframe.

Recommended action

Apps that are impacted by this change use the default Identity UI and have added it in Startup.ConfigureServices as shown in the following code:

csharp

services.AddDefaultIdentity<IdentityUser>()

Take one of the following actions:

Add the MSBuild property IdentityUIFrameworkVersion in the project file and specify Bootstrap 4:
xml
```
<PropertyGroup>
  <TargetFramework>net6.0</TargetFramework>
  <IdentityUIFrameworkVersion>Bootstrap4</IdentityUIFrameworkVersion>
</PropertyGroup>
```
The preceding markup sets the UIFramework version to Bootstrap 4, the same Bootstrap version as used in ASP.NET Core 3.1 and 5.0.
Rename or delete the wwwroot\lib\bootstrap folder and replace it with the wwwroot\lib\bootstrap folder from an ASP.NET Core 6 template-generated app. The Identity templates work with this change but apps using Bootstrap may need to refer to the Bootstrap 5 migration guide.

Affected APIs

xref:Microsoft.Extensions.DependencyInjection.IdentityServiceCollectionUIExtensions.AddDefaultIdentity%60%601(Microsoft.Extensions.DependencyInjection.IServiceCollection)