Added ability for GetConnectionString to handle typical xml App.config or web.config connection string

src/Microsoft.Extensions.Configuration.Abstractions/ConfigurationExtensions.cs

@@ -18,7 +18,18 @@ namespace Microsoft.Extensions.Configuration
         /// <returns></returns>
         public static string GetConnectionString(this IConfiguration configuration, string name)
         {
-            return configuration?.GetSection("ConnectionStrings")?[name];
+            var section = configuration?.GetSection("ConnectionStrings");
+            var result = section?[name];
+
+            if (result != null)
+                return result;
+
+            section = configuration?.GetSection($"connectionStrings:add:{name}:connectionString");
+            if (section != null)
+            {
+                result = section.Value;
+            }
+            return result;
         }
 
         /// <summary>

test/Microsoft.Extensions.Configuration.Test/ConfigurationTest.cs

@@ -264,6 +264,50 @@ namespace Microsoft.Extensions.Configuration.Test
             Assert.Equal("MemVal3", memVal3);
         }
 
+        [Fact]
+        public void CanGetAppConfigConnectionStrings()
+        {
+            // Arrange
+            var dic = new Dictionary<string, string>()
+            {
+                {"connectionStrings:add:DefaultConnection:connectionString", "MemVal"},
+            };
+
+            var memConfigSrc = new MemoryConfigurationSource { InitialData = dic };
+
+            var configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.Add(memConfigSrc);
+
+            var config = configurationBuilder.Build();
+
+            // Act
+            var memVal = config.GetConnectionString("DefaultConnection");
+
+            // Assert
+            Assert.Equal("MemVal", memVal);
+        }
+
+        [Fact]
+        public void GetConnectionStringReturnsNullIfDoesntExist()
+        {
+            // Arrange
+            var dic = new Dictionary<string, string>()
+            {};
+
+            var memConfigSrc = new MemoryConfigurationSource { InitialData = dic };
+
+            var configurationBuilder = new ConfigurationBuilder();
+            configurationBuilder.Add(memConfigSrc);
+
+            var config = configurationBuilder.Build();
+
+            // Act
+            var memVal = config.GetConnectionString("DefaultConnection");
+
+            // Assert
+            Assert.Null(memVal);
+        }
+
         [Fact]
         public void CanGetConfigurationChildren()
         {