Add XML Documentation to ResponseCachingMiddleware and ResponseCachingExtensions (#18968)

* Add XML Documentation to ResponseCachingMiddleware and ResponseCachingExtensions

* Update src/Middleware/ResponseCaching/src/ResponseCachingExtensions.cs

Co-Authored-By: Andrew Stanton-Nurse <andrew@stanton-nurse.com>

* Update src/Middleware/ResponseCaching/src/ResponseCachingExtensions.cs

Co-Authored-By: Andrew Stanton-Nurse <andrew@stanton-nurse.com>

* Update src/Middleware/ResponseCaching/src/ResponseCachingExtensions.cs

Co-Authored-By: Andrew Stanton-Nurse <andrew@stanton-nurse.com>

* Update src/Middleware/ResponseCaching/src/ResponseCachingMiddleware.cs

Co-Authored-By: Andrew Stanton-Nurse <andrew@stanton-nurse.com>

* Update src/Middleware/ResponseCaching/src/ResponseCachingMiddleware.cs

Co-Authored-By: Andrew Stanton-Nurse <andrew@stanton-nurse.com>

* Update ResponseCachingMiddleware.cs

Co-authored-by: Andrew Stanton-Nurse <andrew@stanton-nurse.com>

src/Middleware/ResponseCaching/src/ResponseCachingExtensions.cs

@@ -6,8 +6,15 @@ using Microsoft.AspNetCore.ResponseCaching;
 
 namespace Microsoft.AspNetCore.Builder
 {
+    /// <summary>
+    /// Extension methods for adding the <see cref="ResponseCachingMiddleware"/> to an application.
+    /// </summary>
     public static class ResponseCachingExtensions
     {
+        /// <summary>
+        /// Adds the <see cref="ResponseCachingMiddleware"/> for caching HTTP responses.
+        /// </summary>
+        /// <param name="app">The <see cref="IApplicationBuilder"/>.</param>
         public static IApplicationBuilder UseResponseCaching(this IApplicationBuilder app)
         {
             if (app == null)

src/Middleware/ResponseCaching/src/ResponseCachingMiddleware.cs

@@ -14,6 +14,9 @@ using Microsoft.Net.Http.Headers;
 
 namespace Microsoft.AspNetCore.ResponseCaching
 {
+    /// <summary>
+    /// Enable HTTP response caching.
+    /// </summary>
     public class ResponseCachingMiddleware
     {
         private static readonly TimeSpan DefaultExpirationTimeSpan = TimeSpan.FromSeconds(10);
@@ -29,6 +32,13 @@ namespace Microsoft.AspNetCore.ResponseCaching
         private readonly IResponseCache _cache;
         private readonly IResponseCachingKeyProvider _keyProvider;
 
+        /// <summary>
+        /// Creates a new <see cref="ResponseCachingMiddleware"/>.
+        /// </summary>
+        /// <param name="next">The <see cref="RequestDelegate"/> representing the next middleware in the pipeline.</param>
+        /// <param name="options">The options for this middleware.</param>
+        /// <param name="loggerFactory">The <see cref="ILoggerFactory"/> used for logging.</param>
+        /// <param name="poolProvider">The <see cref="ObjectPoolProvider"/> used for creating <see cref="ObjectPool"/> instances.</param>
         public ResponseCachingMiddleware(
             RequestDelegate next,
             IOptions<ResponseCachingOptions> options,
@@ -88,6 +98,11 @@ namespace Microsoft.AspNetCore.ResponseCaching
             _keyProvider = keyProvider;
         }
 
+        /// <summary>
+        /// Invokes the logic of the middleware.
+        /// </summary>
+        /// <param name="httpContext">The <see cref="HttpContext"/>.</param>
+        /// <returns>A <see cref="Task"/> that completes when the middleware has completed processing.</returns>
         public async Task Invoke(HttpContext httpContext)
         {
             var context = new ResponseCachingContext(httpContext, _logger);