Changes per PR comments

src/Middleware/CORS/src/Infrastructure/CorsMiddleware.cs

@@ -125,11 +125,6 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
                 return _next(context);
             }
 
-            return InvokeCore(context, corsPolicyProvider);
-        }
-
-        private Task InvokeCore(HttpContext context, ICorsPolicyProvider corsPolicyProvider)
-        {
             // CORS policy resolution rules:
             //
             // 1. If there is an endpoint with IDisableCorsAttribute then CORS is not run
@@ -191,13 +186,13 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
             }
 
             return EvaluateAndApplyPolicy(context, corsPolicy);
-        }
 
-        private async Task InvokeCoreAwaited(HttpContext context, Task<CorsPolicy> policyTask)
+            async Task InvokeCoreAwaited(HttpContext context, Task<CorsPolicy> policyTask)
             {
                 var corsPolicy = await policyTask;
                 await EvaluateAndApplyPolicy(context, corsPolicy);
             }
+        }
 
         private Task EvaluateAndApplyPolicy(HttpContext context, CorsPolicy corsPolicy)
         {

src/Middleware/CORS/src/Infrastructure/CorsOptions.cs

@@ -14,8 +14,10 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
     {
         private string _defaultPolicyName = "__DefaultCorsPolicy";
 
+        // DefaultCorsPolicyProvider returns a Task<CorsPolicy>. We'll cache the value to be returned alongside
+        // the actual policy instance to have a separate lookup.
         internal IDictionary<string, (CorsPolicy policy, Task<CorsPolicy> policyTask)> PolicyMap { get; }
-            = new Dictionary<string, (CorsPolicy, Task<CorsPolicy>)>();
+            = new Dictionary<string, (CorsPolicy, Task<CorsPolicy>)>(StringComparer.Ordinal);
 
         public string DefaultPolicyName
         {

src/Middleware/CORS/src/Infrastructure/DefaultCorsPolicyProvider.cs

@@ -11,6 +11,7 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
     /// <inheritdoc />
     public class DefaultCorsPolicyProvider : ICorsPolicyProvider
     {
+        private static readonly Task<CorsPolicy> NullResult = Task.FromResult<CorsPolicy>(null);
         private readonly CorsOptions _options;
 
         /// <summary>
@@ -36,7 +37,7 @@ namespace Microsoft.AspNetCore.Cors.Infrastructure
                 return result.policyTask;
             }
 
-            return Task.FromResult<CorsPolicy>(null);
+            return NullResult;
         }
     }
 }