fix: reject http:// URLs in PostGuardConfig to prevent plaintext credential leaks

E4A.PostGuard.slnx

@@ -1,3 +1,4 @@
 <Solution>
   <Project Path="src/E4A.PostGuard.csproj" />
+  <Project Path="tests/E4A.PostGuard.Tests/E4A.PostGuard.Tests.csproj" />
 </Solution>

src/PostGuard.cs

@@ -8,6 +8,8 @@ public class PostGuard
 
     public PostGuard(PostGuardConfig config)
     {
+        ArgumentNullException.ThrowIfNull(config);
+        config.Validate();
         _config = config;
     }
 

src/PostGuardConfig.cs

@@ -5,4 +5,34 @@ public class PostGuardConfig
     public required string PkgUrl { get; init; }
     public required string CryptifyUrl { get; init; }
     public Dictionary<string, string>? Headers { get; init; }
+
+    /// <summary>
+    /// Opt-in escape hatch to allow non-https URLs (e.g. http://localhost) for
+    /// local development and testing. Defaults to false: the SDK refuses to
+    /// send API keys and signing keys over plaintext connections.
+    /// </summary>
+    public bool AllowInsecureUrls { get; init; }
+
+    internal void Validate()
+    {
+        if (AllowInsecureUrls)
+        {
+            return;
+        }
+
+        RequireHttps(PkgUrl, nameof(PkgUrl));
+        RequireHttps(CryptifyUrl, nameof(CryptifyUrl));
+    }
+
+    private static void RequireHttps(string url, string name)
+    {
+        if (!Uri.TryCreate(url, UriKind.Absolute, out var uri) ||
+            uri.Scheme != Uri.UriSchemeHttps)
+        {
+            throw new ArgumentException(
+                $"{name} must be an absolute https:// URL (got '{url}'). " +
+                "Set AllowInsecureUrls = true to opt in to plaintext URLs for local testing.",
+                name);
+        }
+    }
 }

tests/E4A.PostGuard.Tests/E4A.PostGuard.Tests.csproj

@@ -0,0 +1,25 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.4" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="Xunit" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\E4A.PostGuard.csproj" />
+  </ItemGroup>
+
+</Project>

tests/E4A.PostGuard.Tests/PostGuardConfigTests.cs

@@ -0,0 +1,94 @@
+using E4A.PostGuard;
+
+namespace E4A.PostGuard.Tests;
+
+public class PostGuardConfigTests
+{
+    private const string ValidPkg = "https://pkg.postguard.eu";
+    private const string ValidCryptify = "https://cryptify.postguard.eu";
+
+    [Fact]
+    public void Ctor_AcceptsHttpsUrls()
+    {
+        var config = new PostGuardConfig
+        {
+            PkgUrl = ValidPkg,
+            CryptifyUrl = ValidCryptify,
+        };
+
+        var pg = new PostGuard(config);
+
+        Assert.NotNull(pg);
+    }
+
+    [Theory]
+    [InlineData("http://pkg.postguard.eu")]
+    [InlineData("http://localhost:8080")]
+    [InlineData("ftp://pkg.postguard.eu")]
+    [InlineData("pkg.postguard.eu")]
+    [InlineData("/relative/path")]
+    [InlineData("")]
+    public void Ctor_RejectsNonHttpsPkgUrl(string badUrl)
+    {
+        var config = new PostGuardConfig
+        {
+            PkgUrl = badUrl,
+            CryptifyUrl = ValidCryptify,
+        };
+
+        var ex = Assert.Throws<ArgumentException>(() => new PostGuard(config));
+        Assert.Equal("PkgUrl", ex.ParamName);
+    }
+
+    [Theory]
+    [InlineData("http://cryptify.postguard.eu")]
+    [InlineData("ws://cryptify.postguard.eu")]
+    [InlineData("cryptify.postguard.eu")]
+    public void Ctor_RejectsNonHttpsCryptifyUrl(string badUrl)
+    {
+        var config = new PostGuardConfig
+        {
+            PkgUrl = ValidPkg,
+            CryptifyUrl = badUrl,
+        };
+
+        var ex = Assert.Throws<ArgumentException>(() => new PostGuard(config));
+        Assert.Equal("CryptifyUrl", ex.ParamName);
+    }
+
+    [Fact]
+    public void Ctor_AllowInsecureUrls_AcceptsHttpLocalhost()
+    {
+        var config = new PostGuardConfig
+        {
+            PkgUrl = "http://localhost:8080",
+            CryptifyUrl = "http://localhost:8081",
+            AllowInsecureUrls = true,
+        };
+
+        var pg = new PostGuard(config);
+
+        Assert.NotNull(pg);
+    }
+
+    [Fact]
+    public void Ctor_AllowInsecureUrls_StillAcceptsHttpsUrls()
+    {
+        var config = new PostGuardConfig
+        {
+            PkgUrl = ValidPkg,
+            CryptifyUrl = ValidCryptify,
+            AllowInsecureUrls = true,
+        };
+
+        var pg = new PostGuard(config);
+
+        Assert.NotNull(pg);
+    }
+
+    [Fact]
+    public void Ctor_NullConfig_Throws()
+    {
+        Assert.Throws<ArgumentNullException>(() => new PostGuard(null!));
+    }
+}