Fix SetProvider to return immediately if user-defined provider found

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SqlAuthenticationProviderManager.cs

@@ -186,7 +186,7 @@ public bool SetProvider(SqlAuthenticationMethod authenticationMethod, SqlAuthent
                     if (candidateMethod == authenticationMethod)
                     {
                         _sqlAuthLogger.LogError(nameof(SqlAuthenticationProviderManager), methodName, $"Failed to add provider {GetProviderType(provider)} because a user-defined provider with type {GetProviderType(_providers[authenticationMethod])} already existed for authentication {authenticationMethod}.");
-                        break;
+                        return false; // return here to avoid replacing user-defined provider
                     }
                 }
             }
@@ -206,9 +206,18 @@ public bool SetProvider(SqlAuthenticationMethod authenticationMethod, SqlAuthent
             return true;
         }
 
+        /// <summary>
+        /// Fetches provided configuration section from app.config file.
+        /// Does not support reading from appsettings.json yet.
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="name"></param>
+        /// <returns></returns>
         private static T FetchConfigurationSection<T>(string name)
         {
             Type t = typeof(T);
+
+            // TODO: Support reading configuration from appsettings.json for .NET runtime applications.
             object section = ConfigurationManager.GetSection(name);
             if (section != null)
             {

src/Microsoft.Data.SqlClient/tests/FunctionalTests/AADAuthenticationTests.cs

@@ -5,7 +5,7 @@
 using System;
 using System.Security;
 using System.Threading.Tasks;
-using Microsoft.Identity.Client;
+using Microsoft.Data.SqlClient.FunctionalTests.DataCommon;
 using Xunit;
 
 namespace Microsoft.Data.SqlClient.Tests
@@ -49,6 +49,27 @@ private void InvalidCombinationCheck(SqlCredential credential)
                 Assert.Throws<InvalidOperationException>(() => connection.AccessToken = "SampleAccessToken");
             }
         }
+
+        #if NETFRAMEWORK
+        // This test is only valid for .NET Framework
+
+        /// <summary>
+        /// Tests whether SQL Auth provider is overridden using app.config file.
+        /// This use case is only supported for .NET Framework applications, as driver doesn't support reading configuration from appsettings.json file.
+        /// In future if need be, appsettings.json support can be added.
+        /// </summary>
+        [Fact]
+        public async Task IsDummySqlAuthenticationProviderSetByDefault()
+        {
+            var provider = SqlAuthenticationProvider.GetProvider(SqlAuthenticationMethod.ActiveDirectoryInteractive);
+
+            Assert.NotNull(provider);
+            Assert.Equal(typeof(DummySqlAuthenticationProvider), provider.GetType());
+
+            var token = await provider.AcquireTokenAsync(null);
+            Assert.Equal(token.AccessToken, DummySqlAuthenticationProvider.DUMMY_TOKEN_STR);
+        }
+        #endif
 
         [Fact]
         public void CustomActiveDirectoryProviderTest()

src/Microsoft.Data.SqlClient/tests/FunctionalTests/DataCommon/DummySqlAuthenticationProvider.cs

@@ -0,0 +1,27 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.Data.SqlClient.FunctionalTests.DataCommon
+{
+    /// <summary>
+    /// Dummy class to override default Sql Authentication provider in functional tests.
+    /// This type returns a dummy access token and is only used for registration test from app.config file.
+    /// Since no actual connections are intended to be made in Functional tests, 
+    /// this type is added by default to validate config file registration scenario.
+    /// </summary>
+    public class DummySqlAuthenticationProvider : SqlAuthenticationProvider
+    {
+        public static string DUMMY_TOKEN_STR = "dummy_access_token";
+
+        public override Task<SqlAuthenticationToken> AcquireTokenAsync(SqlAuthenticationParameters parameters)
+        => Task.FromResult(new SqlAuthenticationToken(DUMMY_TOKEN_STR, new DateTimeOffset(DateTime.Now.AddHours(2))));
+
+        // Supported authentication modes don't matter for dummy test, but added to demonstrate config file usage.
+        public override bool IsSupported(SqlAuthenticationMethod authenticationMethod)
+        => authenticationMethod == SqlAuthenticationMethod.ActiveDirectoryInteractive;
+    }
+}

src/Microsoft.Data.SqlClient/tests/FunctionalTests/Microsoft.Data.SqlClient.FunctionalTests.csproj

@@ -24,6 +24,7 @@
     <Compile Include="AlwaysEncryptedTests\Utility.cs" />
     <Compile Include="AssertExtensions.cs" />
     <Compile Include="DataCommon\AssemblyResourceManager.cs" />
+    <Compile Include="DataCommon\DummySqlAuthenticationProvider.cs" />
     <Compile Include="DataCommon\SystemDataResourceManager.cs" />
     <Compile Include="DataCommon\TestUtility.cs" />
     <Compile Include="LocalizationTest.cs" />
@@ -71,6 +72,11 @@
     <Compile Include="..\..\src\Microsoft\Data\SqlClient\TdsParserStateObject.Multiplexer.cs" />
     <Compile Include="..\..\src\Microsoft\Data\SqlClient\Packet.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetGroup)' == 'netfx'">
+    <None Update="app.config">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
   <!-- XUnit and XUnit extensions -->
   <ItemGroup>
     <PackageReference Include="Microsoft.DotNet.XUnitExtensions" />
@@ -91,6 +97,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" />
     <PackageReference Include="Microsoft.SqlServer.Types" />
     <PackageReference Include="Newtonsoft.Json" />
+    <PackageReference Include="System.Configuration.ConfigurationManager" />
     <PackageReference Include="System.Security.Cryptography.Pkcs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetGroup)' == 'netcoreapp'">

src/Microsoft.Data.SqlClient/tests/FunctionalTests/SqlAuthenticationProviderTest.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using Microsoft.Data.SqlClient.FunctionalTests.DataCommon;
 using Xunit;
 
 namespace Microsoft.Data.SqlClient.Tests
@@ -11,7 +12,6 @@ public class SqlAuthenticationProviderTest
         [Theory]
         [InlineData(SqlAuthenticationMethod.ActiveDirectoryIntegrated)]
         [InlineData(SqlAuthenticationMethod.ActiveDirectoryPassword)]
-        [InlineData(SqlAuthenticationMethod.ActiveDirectoryInteractive)]
         [InlineData(SqlAuthenticationMethod.ActiveDirectoryServicePrincipal)]
         [InlineData(SqlAuthenticationMethod.ActiveDirectoryDeviceCodeFlow)]
         [InlineData(SqlAuthenticationMethod.ActiveDirectoryManagedIdentity)]
@@ -22,5 +22,18 @@ public void DefaultAuthenticationProviders(SqlAuthenticationMethod method)
         {
             Assert.IsType<ActiveDirectoryAuthenticationProvider>(SqlAuthenticationProvider.GetProvider(method));
         }
+
+        #if NETFRAMEWORK
+        // This test is only valid for .NET Framework
+
+        // Overridden by app.config in this project
+        [Theory]
+        [InlineData(SqlAuthenticationMethod.ActiveDirectoryInteractive)]
+        public void DefaultAuthenticationProviders_Interactive(SqlAuthenticationMethod method)
+        {
+            Assert.IsType<DummySqlAuthenticationProvider>(SqlAuthenticationProvider.GetProvider(method));
+        }
+
+        #endif
     }
 }

src/Microsoft.Data.SqlClient/tests/FunctionalTests/app.config

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<!-- Application configuration file is loaded by the compiler first before loading managed types. -->
+<configuration>
+  <configSections>
+    <section name="SqlClientAuthenticationProviders" type="Microsoft.Data.SqlClient.SqlClientAuthenticationProviderConfigurationSection,Microsoft.Data.SqlClient" />
+  </configSections>
+  <!-- Custom authentication providers from app.config are loaded by the SqlAuthenticationProviderManager before registering default authentication provider. -->
+  <SqlClientAuthenticationProviders>
+    <providers>
+      <add name="active directory interactive" type="Microsoft.Data.SqlClient.FunctionalTests.DataCommon.DummySqlAuthenticationProvider, FunctionalTests" />
+    </providers>
+  </SqlClientAuthenticationProviders>
+</configuration>