Add XML docs to IHttpContextAccessor and IHttpContextFactory (#14747)

src/Http/Http.Abstractions/src/IHttpContextAccessor.cs

@@ -3,8 +3,18 @@
 
 namespace Microsoft.AspNetCore.Http
 {
+    /// <summary>
+    /// Provides access to the current <see cref="HttpContext"/>, if one is available.
+    /// </summary>
+    /// <remarks>
+    /// This interface should be used with caution. It relies on <see cref="System.Threading.AsyncLocal{T}" /> which can have a negative performance impact on async calls.
+    /// It also creates a dependency on "ambient state" which can make testing more difficult.
+    /// </remarks>
     public interface IHttpContextAccessor
     {
+        /// <summary>
+        /// Gets or sets the current <see cref="HttpContext"/>. Returns <see langword="null" /> if there is no active <see cref="HttpContext" />.
+        /// </summary>
         HttpContext HttpContext { get; set; }
     }
-}
+}

src/Http/Http.Abstractions/src/IHttpContextFactory.cs

@@ -5,9 +5,22 @@ using Microsoft.AspNetCore.Http.Features;
 
 namespace Microsoft.AspNetCore.Http
 {
+    /// <summary>
+    /// Provides methods to create and dispose of <see cref="HttpContext"/> instances.
+    /// </summary>
     public interface IHttpContextFactory
     {
+        /// <summary>
+        /// Creates an <see cref="HttpContext"/> instance for the specified set of HTTP features.
+        /// </summary>
+        /// <param name="featureCollection">The collection of HTTP features to set on the created instance.</param>
+        /// <returns>The <see cref="HttpContext"/> instance.</returns>
         HttpContext Create(IFeatureCollection featureCollection);
+
+        /// <summary>
+        /// Releases resources held by the <see cref="HttpContext"/>.
+        /// </summary>
+        /// <param name="httpContext">The <see cref="HttpContext"/> to dispose.</param>
         void Dispose(HttpContext httpContext);
     }
 }