Unescape query parameter name

Author: campersau

src/Http/WebUtilities/src/QueryHelpers.cs

@@ -218,7 +218,10 @@ public static Dictionary<string, StringValues> ParseQuery(string? queryString)
                 {
                     if (delimiterIndex > scanIndex)
                     {
-                        accumulator.Append(queryString.Substring(scanIndex, delimiterIndex - scanIndex), string.Empty);
+                        string name = queryString.Substring(scanIndex, delimiterIndex - scanIndex);
+                        accumulator.Append(
+                            Uri.UnescapeDataString(name.Replace('+', ' ')),
+                            string.Empty);
                     }
                 }
                 scanIndex = delimiterIndex + 1;

src/Http/WebUtilities/test/QueryHelpersTests.cs

@@ -55,6 +55,14 @@ public void ParseQueryWithEmptyKeyWorks()
             Assert.Equal(new[] { "value1", "" }, collection[""]);
         }
 
+        [Fact]
+        public void ParseQueryWithEncodedKeyWorks()
+        {
+            var collection = QueryHelpers.ParseQuery("?fields%5BtodoItems%5D");
+            Assert.Single(collection);
+            Assert.Equal("", collection["fields[todoItems]"].FirstOrDefault());
+        }
+
         [Theory]
         [InlineData("?")]
         [InlineData("")]