title: IClaimsTransformation not firing
body: <p>I've tried to implement an <code>IClaimsTransformation</code> class I found in my ASP.NET CORE 3.1 web app</p>
  <pre><code>public class ClaimsTransformer : IClaimsTransformation
  {
      public ClaimsTransformer(IHttpContextAccessor httpAccessor) { }
  
      public Task&lt;ClaimsPrincipal&gt; TransformAsync(ClaimsPrincipal p)
      {
          p.AddIdentity(new ClaimsIdentity());
          return Task.FromResult(p);
      }
  }
  </code></pre>
  <p>And I've added it like so:</p>
  <pre><code>    public void ConfigureServices(IServiceCollection services)
      {
  
          services.AddDbContext&lt;ApplicationDbContext&gt;(options =&gt;
              options.UseSqlServer(Configuration.GetConnectionString(&quot;MyConString&quot;)));
  
          services.AddAuthentication(IISDefaults.AuthenticationScheme);
  
          services.AddSingleton&lt;IClaimsTransformation, ClaimsTransformer&gt;();
  
          services.AddIdentity&lt;IdentityUser, IdentityRole&gt;()
              .AddRoleManager&lt;RoleManager&lt;IdentityRole&gt;&gt;()
              .AddEntityFrameworkStores&lt;ApplicationDbContext&gt;()
              .AddDefaultTokenProviders();
  
          ...
  </code></pre>
  <p>And while the constructor gets hit during startup, the <code>TransformAsync()</code> method never fires when visitng a controller. What am I missing? There are several implementations adding <code>IClaimsTransformation</code> but none of them have any more info other than the class and adding via singleton / transient</p>
  <p>Although I should add I've seen various examples of <code>app.UseClaimsTransformation()</code> but that's not available in 3.1</p>