Creating a testable service that accesses the current ClaimsPrincipal

gistfile1.cs

public interface ICurrentPrincipalAccessor {
  ClaimsPrincipal CurrentPrincipal { get; }
}

public class HttpContextCurrentPrincipalAccessor : ICurrentPrincipalAccessor {
  private IHttpContextAccessor _httpContextAccessor;
  
  public HttpContextCurrentPrincipalAccessor(IHttpContextAccessor httpContextAccessor) {
    _httpContextAccessor = httpContextAccessor;
  }
  
  public ClaimsPrincipal CurrentPrincipal { get { return _httpContextAccessor.HttpContext.User; }  }
}

// In Startup.cs

public IServiceProvider  ConfigureServices(IServiceCollection services) {
 // everything else...
 services.AddSingleton<ICurrentPrincipalAccessor, HttpContextCurrentPrincipalAccessor>();
}

// In your service class

public class MyTestableServiceClass {
  private ICurrentPrincipalAccessor _currentPrincipalAccessor;
  public MyTestableServiceClass(ICurrentPrincipalAccessor currentPrincipalAccessor) {
    _currentPrincipalAccessor = currentPrincipalAccessor;
  }
  
  public void MyServiceMethod() {
    var userId = _currentPrincipalAccessor.CurrentPrincipal.GetUserId();
    // ... etc
  }
}

How do I access _currentPrincipalAccessor from my DbContext? So I can apply _currentPrincipalAccessor.CurrentPrincipal.GetUserId() to the Auditable information when persisting the data to a db.

I just placed _currentPrincipalAccessor in my DbContext and it worked out fine. I am also using IDesignTimeDbContextFactory, but this uses a second constructor which does not assign a value to the instance _currentPrincipalAccessor. Since the IdesignTimeDbContextFactory will not me making any changes to the database it should be fine.