feat(#13): S-12c-1 — behandel BFF auth + werkbak (ADR-0013) (#85)

## What & why

First half of **S-12c** (behandel-portal backend), per **ADR-0013** (decisions recorded in #84):

- **BFF multi-realm auth.** A second JWT bearer scheme (`medewerker`) alongside the default `digid` scheme. On validation it lifts Keycloak's `realm_access.roles` onto the principal, and a `behandelaar` policy (medewerker scheme + `behandelaar` role) gates `/behandel/*`. Self-service keeps the digid scheme.
- **Werkbak = Flowable tasks.** The domain `Werkbak` query reads the open `Beoordelen` tasks (§8.2, S-12b's `IUserTaskClient`) and enriches each with its aggregate's bsn + status; `GET /behandel/werkbak` (domain) is proxied by the BFF `GET /behandel/werkbak` behind the behandelaar policy. The read projection stays the anonymous openbaar model (no premature `IN_BEHANDELING`/personal-data plumbing — deferred in ADR-0008).

Behavior: `/behandel/werkbak` is **401** without a token, **403** for a medewerker lacking the role, **200 + werkbak** for a behandelaar.

**S-12c-2** (next): `POST /behandel/registrations/{id}/decide` → domain decision + complete the Flowable task.

## Definition of Done

- [x] Linked issue: #13 (umbrella, `refs`); closes the adr-proposal #84
- [x] Tests first; red → green per layer
- [x] Unit + acceptance green (`make unit`): domain 78, bff 23, acceptance 9 (+ acl/event-subscriber unaffected)
- [x] api-client `test` green; openapi.json regenerated (drift guard passes)
- [x] Mutation ≥ break(90): **domain 100%, bff 100%**
- [x] ADR-0013 added; `Keycloak__MedewerkerAuthority` wired into compose
- [ ] CI green (pending)

Part of #13. closes #84

Reviewed-on: #85

services/bff/Bff.Tests/BffFactory.cs

@@ -5,6 +5,7 @@ using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc.Testing;
 using Microsoft.AspNetCore.TestHost;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.IdentityModel.Protocols;
 using Microsoft.IdentityModel.Protocols.OpenIdConnect;
 using Microsoft.IdentityModel.Tokens;
 
@@ -23,9 +24,34 @@ internal sealed class BffFactory : WebApplicationFactory<Program>
     public FakeDomainClient Domain { get; } = new();
     public FakeProjectionClient Projection { get; } = new();
 
+    private static void ValidateWithTestKey(IServiceCollection services, string scheme) =>
+        services.Configure<JwtBearerOptions>(scheme, options =>
+        {
+            // Validate locally against the test key and NEVER reach out for OIDC metadata. A static
+            // configuration manager guarantees this regardless of Configure/PostConfigure ordering —
+            // clearing Authority alone left the medewerker scheme fetching metadata under CI timing
+            // (2s hang → 401), because JwtBearer's PostConfigure could still build a ConfigurationManager.
+            options.Authority = null;
+            options.MetadataAddress = null!;
+            options.RequireHttpsMetadata = false;
+            options.Configuration = new OpenIdConnectConfiguration();
+            options.ConfigurationManager =
+                new StaticConfigurationManager<OpenIdConnectConfiguration>(new OpenIdConnectConfiguration());
+            options.TokenValidationParameters = new TokenValidationParameters
+            {
+                ValidateIssuer = false,
+                ValidateAudience = false,
+                ValidateLifetime = true,
+                ValidateIssuerSigningKey = true,
+                IssuerSigningKey = TestSigningKey,
+                ClockSkew = TimeSpan.Zero,
+            };
+        });
+
     protected override void ConfigureWebHost(IWebHostBuilder builder)
     {
         builder.UseSetting("Keycloak:Authority", "https://keycloak.invalid/realms/digid");
+        builder.UseSetting("Keycloak:MedewerkerAuthority", "https://keycloak.invalid/realms/medewerker");
         builder.UseSetting("Downstream:Domain:BaseUrl", "http://domain.invalid/");
         builder.UseSetting("Downstream:Projection:BaseUrl", "http://projection.invalid/");
 
@@ -34,23 +60,11 @@ internal sealed class BffFactory : WebApplicationFactory<Program>
             services.AddSingleton<IDomainClient>(Domain);
             services.AddSingleton<IProjectionClient>(Projection);
 
-            services.Configure<JwtBearerOptions>(JwtBearerDefaults.AuthenticationScheme, options =>
-            {
-                // Validate locally against the test key; never reach out for OIDC metadata.
-                options.Authority = null;
-                options.MetadataAddress = null!;
-                options.RequireHttpsMetadata = false;
-                options.Configuration = new OpenIdConnectConfiguration();
-                options.TokenValidationParameters = new TokenValidationParameters
-                {
-                    ValidateIssuer = false,
-                    ValidateAudience = false,
-                    ValidateLifetime = true,
-                    ValidateIssuerSigningKey = true,
-                    IssuerSigningKey = TestSigningKey,
-                    ClockSkew = TimeSpan.Zero,
-                };
-            });
+            // Both realms validate locally against the test key (no live Keycloak). The medewerker
+            // scheme keeps its OnTokenValidated role-lifting from Program.cs — only the validation
+            // parameters are swapped here.
+            ValidateWithTestKey(services, JwtBearerDefaults.AuthenticationScheme);
+            ValidateWithTestKey(services, "medewerker");
         });
     }
 }
@@ -60,12 +74,16 @@ internal sealed class FakeDomainClient : IDomainClient
 {
     public string? SubmittedBsn { get; private set; }
     public SubmitAccepted Result { get; set; } = new("reg-123", "Ingediend");
+    public List<WerkbakItem> Werkbak { get; } = [];
 
     public Task<SubmitAccepted> SubmitRegistrationAsync(string bsn, CancellationToken ct = default)
     {
         SubmittedBsn = bsn;
         return Task.FromResult(Result);
     }
+
+    public Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default)
+        => Task.FromResult<IReadOnlyList<WerkbakItem>>(Werkbak);
 }
 
 /// <summary>Serves a configurable set of projection rows.</summary>