[ANCM] Add switch to prefer env over web.config (#19746)

src/Servers/IIS/AspNetCoreModuleV2/RequestHandlerLib/environmentvariablehash.h

@@ -13,6 +13,7 @@
 #define ASPNETCORE_IIS_AUTH_BASIC                   L"basic;"
 #define ASPNETCORE_IIS_AUTH_ANONYMOUS               L"anonymous;"
 #define ASPNETCORE_IIS_AUTH_NONE                    L"none"
+#define ANCM_PREFER_ENVIRONMENT_VARIABLES_ENV_STR   L"ANCM_PREFER_ENVIRONMENT_VARIABLES"
 
 //
 // The key used for hash-table lookups, consists of the port on which the http process is created.

src/Servers/IIS/AspNetCoreModuleV2/RequestHandlerLib/environmentvariablehelpers.h

@@ -78,9 +78,27 @@ public:
             environmentVariables.insert_or_assign(HOSTING_STARTUP_ASSEMBLIES_ENV_STR, hostingStartupValues);
         }
 
+        auto preferEnvironmentVariablesSetting = Environment::GetEnvironmentVariableValue(ANCM_PREFER_ENVIRONMENT_VARIABLES_ENV_STR).value_or(L"false");
+        auto preferEnvironmentVariables = equals_ignore_case(L"1", preferEnvironmentVariablesSetting) || equals_ignore_case(L"true", preferEnvironmentVariablesSetting);
+
         for (auto& environmentVariable : environmentVariables)
         {
-            environmentVariable.second = Environment::ExpandEnvironmentVariables(environmentVariable.second);
+            if (preferEnvironmentVariables)
+            {
+                auto env = Environment::GetEnvironmentVariableValue(environmentVariable.first);
+                if (env.has_value())
+                {
+                    environmentVariable.second = env.value();
+                }
+                else
+                {
+                    environmentVariable.second = Environment::ExpandEnvironmentVariables(environmentVariable.second);
+                }
+            }
+            else
+            {
+                environmentVariable.second = Environment::ExpandEnvironmentVariables(environmentVariable.second);
+            }
         }
 
         return environmentVariables;

src/Servers/IIS/IIS/test/Common.FunctionalTests/Inprocess/EnvironmentVariableTests.cs

@@ -126,5 +126,22 @@ namespace Microsoft.AspNetCore.Server.IIS.FunctionalTests.InProcess
             deploymentParameters.WebConfigBasedEnvironmentVariables["OtherVariable"] = "%TestVariable%;Hello";
             Assert.Equal("World;Hello", await GetStringAsync(deploymentParameters, "/GetEnvironmentVariable?name=OtherVariable"));
         }
+
+        [ConditionalTheory]
+        [RequiresIIS(IISCapability.PoolEnvironmentVariables)]
+        [RequiresNewHandler]
+        [RequiresNewShim]
+        [InlineData(HostingModel.InProcess)]
+        [InlineData(HostingModel.OutOfProcess)]
+        public async Task PreferEnvironmentVariablesOverWebConfigWhenConfigured(HostingModel hostingModel)
+        {
+            var deploymentParameters = Fixture.GetBaseDeploymentParameters(hostingModel);
+
+            var environment = "Development";
+            deploymentParameters.EnvironmentVariables["ANCM_PREFER_ENVIRONMENT_VARIABLES"] = "true";
+            deploymentParameters.EnvironmentVariables["ASPNETCORE_ENVIRONMENT"] = environment;
+            deploymentParameters.WebConfigBasedEnvironmentVariables.Add("ASPNETCORE_ENVIRONMENT", "Debug");
+            Assert.Equal(environment, await GetStringAsync(deploymentParameters, "/GetEnvironmentVariable?name=ASPNETCORE_ENVIRONMENT"));
+        }
     }
 }

src/Servers/IIS/IIS/test/IIS.Shared.FunctionalTests/RequiresIISAttribute.cs

@@ -61,6 +61,11 @@ namespace Microsoft.AspNetCore.Server.IIS.FunctionalTests
 
             var ancmConfigPath = Path.Combine(Environment.SystemDirectory, "inetsrv", "config", "schema", "aspnetcore_schema.xml");
 
+            if (!File.Exists(ancmConfigPath))
+            {
+                ancmConfigPath = Path.Combine(Environment.SystemDirectory, "inetsrv", "config", "schema", "aspnetcore_schema_v2.xml");
+            }
+
             if (!File.Exists(ancmConfigPath) && !SkipInVSTSAttribute.RunningInVSTS)
             {
                 _skipReasonStatic = "IIS Schema is not installed.";