Add SGU credential provider and authentication broker

tests/SGU.CredentialProvider.Tests/BrokerClientTests.cs

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+using System.Net;
+using System.Text;
+using System.Text.Json;
+using Xunit;
+
+namespace SGU.CredentialProvider.Tests;
+
+public sealed class BrokerClientTests
+{
+    [Fact]
+    public async Task SendsTheOriginalPasswordWithoutDerivation()
+    {
+        const string original = "Exacta-Árbol-🔐-27!";
+        CapturingHandler handler = new(HttpStatusCode.OK, """
+            {"domain":"LCI","username":"DO123456","upn":"DO123456@lci.lasalle.mx","created":true,"moved":false}
+            """);
+        using BrokerClient client = new(CreateSettings(), handler);
+
+        BrokerDecision decision = await client.AuthenticateAsync(
+            "DO123456",
+            original,
+            TestContext.Current.CancellationToken);
+
+        Assert.Equal(BrokerDecisionKind.Authorized, decision.Kind);
+        using JsonDocument requestJson = JsonDocument.Parse(handler.RequestBody);
+        Assert.Equal(original, requestJson.RootElement.GetProperty("password").GetString());
+        Assert.DoesNotContain("derived", handler.RequestBody, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Fact]
+    public async Task ExplicitUnauthorizedResponseStopsTheLogin()
+    {
+        using BrokerClient client = new(
+            CreateSettings(),
+            new CapturingHandler(HttpStatusCode.Unauthorized, "{\"code\":\"INVALID_INSTITUTIONAL_CREDENTIALS\"}"));
+
+        BrokerDecision decision = await client.AuthenticateAsync(
+            "AL123456",
+            "Wrong",
+            TestContext.Current.CancellationToken);
+
+        Assert.Equal(BrokerDecisionKind.InvalidCredentials, decision.Kind);
+    }
+
+    [Fact]
+    public async Task BrokerOutageRequestsWindowsCachedCredentialFallback()
+    {
+        using BrokerClient client = new(
+            CreateSettings(),
+            new CapturingHandler(HttpStatusCode.ServiceUnavailable, "{\"code\":\"NTLM_UPSTREAM_ERROR\"}"));
+
+        BrokerDecision decision = await client.AuthenticateAsync(
+            "AD123456",
+            "LastKnown",
+            TestContext.Current.CancellationToken);
+
+        Assert.Equal(BrokerDecisionKind.Unavailable, decision.Kind);
+    }
+
+    private static ProviderSettings CreateSettings() => new()
+    {
+        BrokerEndpoint = new Uri("https://broker.example.test/v1/authenticate"),
+        DomainNetbios = "LCI",
+        TimeoutSeconds = 5,
+        ClientCertificateThumbprint = new string('A', 40),
+        ServerCertificateThumbprint = new string('B', 40)
+    };
+
+    private sealed class CapturingHandler(HttpStatusCode statusCode, string responseBody) : HttpMessageHandler
+    {
+        public string RequestBody { get; private set; } = string.Empty;
+
+        protected override async Task<HttpResponseMessage> SendAsync(
+            HttpRequestMessage request,
+            CancellationToken cancellationToken)
+        {
+            RequestBody = request.Content is null
+                ? string.Empty
+                : await request.Content.ReadAsStringAsync(cancellationToken);
+
+            return new HttpResponseMessage(statusCode)
+            {
+                Content = new StringContent(responseBody, Encoding.UTF8, "application/json")
+            };
+        }
+    }
+}

tests/SGU.CredentialProvider.Tests/SGU.CredentialProvider.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net10.0-windows</TargetFramework>
+    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\SGU.CredentialProvider\SGU.CredentialProvider.csproj" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.9.0" />
+    <PackageReference Include="xunit.v3" Version="4.0.0" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.0">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+</Project>