[Blazor] Add environment variables to IConfiguration by default in WebAssemblyHostBuilder (#64578)

Author: Copilot

src/Components/WebAssembly/WebAssembly/src/Hosting/WebAssemblyHostBuilder.cs

@@ -52,6 +52,11 @@ public static WebAssemblyHostBuilder CreateDefault(string[]? args = default)
 
         WebAssemblyCultureProvider.Initialize();
 
+        // Add environment variables to configuration by default.
+        // This aligns WebAssembly behavior with server-side ASP.NET Core applications
+        // where environment variables are automatically included in IConfiguration.
+        builder.Configuration.AddEnvironmentVariables();
+
         // Right now we don't have conventions or behaviors that are specific to this method
         // however, making this the default for the template allows us to add things like that
         // in the future, while giving `new WebAssemblyHostBuilder` as an opt-out of opinionated

src/Components/WebAssembly/WebAssembly/src/Microsoft.AspNetCore.Components.WebAssembly.csproj

@@ -17,6 +17,7 @@
 
   <ItemGroup>
     <Reference Include="Microsoft.AspNetCore.Components.Web" />
+    <Reference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" />
     <Reference Include="Microsoft.Extensions.Configuration.Json" />
     <Reference Include="Microsoft.Extensions.Configuration.Binder" />
     <Reference Include="Microsoft.Extensions.Logging" />

src/Components/WebAssembly/WebAssembly/test/Hosting/WebAssemblyHostBuilderTest.cs

@@ -310,4 +310,35 @@ private class CircularServiceB
     {
         public CircularServiceB(CircularServiceA serviceA) { }
     }
+
+    [Fact]
+    public void Configuration_IncludesEnvironmentVariables_WhenAddedExplicitly()
+    {
+        // Arrange
+        var testEnvVarKey = $"TEST_WASM_CONFIG_{Guid.NewGuid():N}";
+        var testEnvVarValue = "test-value-12345";
+
+        try
+        {
+            // Set an environment variable before creating the builder
+            Environment.SetEnvironmentVariable(testEnvVarKey, testEnvVarValue);
+
+            var builder = new WebAssemblyHostBuilder(new TestInternalJSImportMethods());
+
+            // This mimics what CreateDefault now does
+            builder.Configuration.AddEnvironmentVariables();
+
+            // Act
+            var host = builder.Build();
+
+            // Assert
+            var configuration = host.Services.GetRequiredService<IConfiguration>();
+            Assert.Equal(testEnvVarValue, configuration[testEnvVarKey]);
+        }
+        finally
+        {
+            // Clean up the environment variable
+            Environment.SetEnvironmentVariable(testEnvVarKey, null);
+        }
+    }
 }