From 06b699ec5c6df6200b393c4f418be347bf3650fc Mon Sep 17 00:00:00 2001
From: Waldek Mastykarz <waldek@mastykarz.nl>
Date: Wed, 21 Oct 2026 15:55:41 +0200
Subject: [PATCH] Report unset API Center environment variables. Closes #1968

When an API Center setting references an environment variable with
@NAME and the variable isn't set, throw an error naming the variable
instead of silently using the literal @NAME value.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 53023532-b4f0-4cd7-a238-b890b15ce83a
---
 .../ApiCenterClientTests.cs                   | 52 +++++++++++++++++++
 DevProxy.Plugins/ApiCenter/ApiCenterClient.cs | 34 ++++++------
 2 files changed, 70 insertions(+), 16 deletions(-)
 create mode 100644 DevProxy.Integration.Tests/ApiCenterClientTests.cs

diff --git a/DevProxy.Integration.Tests/ApiCenterClientTests.cs b/DevProxy.Integration.Tests/ApiCenterClientTests.cs
new file mode 100644
index 000000000..f1f6164ca
--- /dev/null
+++ b/DevProxy.Integration.Tests/ApiCenterClientTests.cs
@@ -0,0 +1,52 @@
+// 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 DevProxy.Plugins.ApiCenter;
+using Microsoft.Extensions.Logging.Abstractions;
+using Xunit;
+
+namespace DevProxy.Integration.Tests;
+
+public class ApiCenterClientTests
+{
+    private const string VariableName = "DEVPROXY_TEST_APICENTER_SUBSCRIPTION_ID";
+
+    [Fact]
+    public void Constructor_UnsetEnvironmentVariable_Throws()
+    {
+        Environment.SetEnvironmentVariable(VariableName, null);
+
+        var ex = Assert.Throws<ArgumentException>(() => CreateClient($"@{VariableName}"));
+
+        Assert.Contains(VariableName, ex.Message, StringComparison.Ordinal);
+        Assert.Contains("subscriptionId", ex.Message, StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void Constructor_SetEnvironmentVariable_UsesItsValue()
+    {
+        Environment.SetEnvironmentVariable(VariableName, "00000000-0000-0000-0000-000000000000");
+        try
+        {
+            var configuration = NewConfiguration($"@{VariableName}");
+            using var client = new ApiCenterClient(configuration, NullLogger<ApiCenterClient>.Instance);
+
+            Assert.Equal("00000000-0000-0000-0000-000000000000", configuration.SubscriptionId);
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable(VariableName, null);
+        }
+    }
+
+    private static ApiCenterClient CreateClient(string subscriptionId) =>
+        new(NewConfiguration(subscriptionId), NullLogger<ApiCenterClient>.Instance);
+
+    private static ApiCenterClientConfiguration NewConfiguration(string subscriptionId) => new()
+    {
+        SubscriptionId = subscriptionId,
+        ResourceGroupName = "rg",
+        ServiceName = "svc"
+    };
+}
diff --git a/DevProxy.Plugins/ApiCenter/ApiCenterClient.cs b/DevProxy.Plugins/ApiCenter/ApiCenterClient.cs
index 0116c9bdc..0ca431749 100644
--- a/DevProxy.Plugins/ApiCenter/ApiCenterClient.cs
+++ b/DevProxy.Plugins/ApiCenter/ApiCenterClient.cs
@@ -56,22 +56,10 @@ internal ApiCenterClient(ApiCenterClientConfiguration configuration, ILogger<Api
         }
 
         // load configuration from env vars
-        if (configuration.SubscriptionId.StartsWith('@'))
-        {
-            configuration.SubscriptionId = Environment.GetEnvironmentVariable(configuration.SubscriptionId[1..]) ?? configuration.SubscriptionId;
-        }
-        if (configuration.ResourceGroupName.StartsWith('@'))
-        {
-            configuration.ResourceGroupName = Environment.GetEnvironmentVariable(configuration.ResourceGroupName[1..]) ?? configuration.ResourceGroupName;
-        }
-        if (configuration.ServiceName.StartsWith('@'))
-        {
-            configuration.ServiceName = Environment.GetEnvironmentVariable(configuration.ServiceName[1..]) ?? configuration.ServiceName;
-        }
-        if (configuration.WorkspaceName.StartsWith('@'))
-        {
-            configuration.WorkspaceName = Environment.GetEnvironmentVariable(configuration.WorkspaceName[1..]) ?? configuration.WorkspaceName;
-        }
+        configuration.SubscriptionId = ResolveEnvironmentVariable(configuration.SubscriptionId, "subscriptionId");
+        configuration.ResourceGroupName = ResolveEnvironmentVariable(configuration.ResourceGroupName, "resourceGroupName");
+        configuration.ServiceName = ResolveEnvironmentVariable(configuration.ServiceName, "serviceName");
+        configuration.WorkspaceName = ResolveEnvironmentVariable(configuration.WorkspaceName, "workspaceName");
 
         _configuration = configuration;
         _logger = logger;
@@ -91,6 +79,20 @@ internal ApiCenterClient(ApiCenterClientConfiguration configuration, ILogger<Api
         }
     }
 
+    private static string ResolveEnvironmentVariable(string value, string settingName)
+    {
+        if (!value.StartsWith('@'))
+        {
+            return value;
+        }
+
+        var variableName = value[1..];
+        var variableValue = Environment.GetEnvironmentVariable(variableName);
+        return string.IsNullOrEmpty(variableValue)
+            ? throw new ArgumentException($"Environment variable {variableName} referenced by {settingName} isn't set.")
+            : variableValue;
+    }
+
     internal Task<string?> GetAccessTokenAsync(CancellationToken cancellationToken) =>
         _authenticationHandler.GetAccessTokenAsync(cancellationToken);