services/acl/Acl.Api/Program.cs

@@ -33,6 +33,15 @@ builder.Services.AddSingleton(sp => sp.GetRequiredService<IConfiguration>()
 builder.Services.AddSingleton(sp => sp.GetRequiredService<IConfiguration>()
     .GetSection("Acl:OpenZaak").Get<OpenZaakOptions>()
     ?? throw new InvalidOperationException("Missing configuration section 'Acl:OpenZaak'"));
+// The default-fill values are held in a runtime-mutable store (S-15b, ADR-0026), seeded from the
+// configured Acl:Defaults. The beheer portal edits it; the worker reads it per zaak. The S-27
+// resolution keys stay on AclDefaults (static) — see DefaultFillSettings.
+builder.Services.AddSingleton<IDefaultFillStore>(sp =>
+{
+    var d = sp.GetRequiredService<AclDefaults>();
+    return new InMemoryDefaultFillStore(
+        new DefaultFillSettings(d.Bronorganisatie, d.VerantwoordelijkeOrganisatie, d.Vertrouwelijkheidaanduiding));
+});
 builder.Services.AddHttpClient<IZaakGateway, OpenZaakGateway>();
 // Singleton so the resolved zaaktype/informatieobjecttype URLs are cached across requests (S-27).
 builder.Services.AddSingleton<IZaaktypeCatalog, CachedZaaktypeCatalog>();
@@ -91,6 +100,22 @@ app.MapPost("/documenten", async (StoreDocumentRequest body, AclService acl, Can
 app.MapGet("/catalogi/zaaktypen", async (AclService acl, CancellationToken ct) =>
     Results.Ok(await acl.ListZaaktypenAsync(ct)));
 
+// Read the current default-fill settings (beheer config viewer, S-15b).
+app.MapGet("/default-fill", (AclService acl) => Results.Ok(acl.GetDefaultFill()));
+
+// Update the default-fill settings from the beheer portal (S-15b). Behind beheerder authorization at
+// the BFF; the ACL validates the values are present (the three ZGW-mandatory fields).
+app.MapPut("/default-fill", (DefaultFillSettings body, AclService acl) =>
+{
+    if (string.IsNullOrWhiteSpace(body.Bronorganisatie) ||
+        string.IsNullOrWhiteSpace(body.VerantwoordelijkeOrganisatie) ||
+        string.IsNullOrWhiteSpace(body.Vertrouwelijkheidaanduiding))
+        return Results.BadRequest(new { error = "bronorganisatie, verantwoordelijkeOrganisatie and vertrouwelijkheidaanduiding are all required." });
+
+    acl.UpdateDefaultFill(body);
+    return Results.NoContent();
+});
+
 app.Run();
 
 public sealed record OpenZaakRequest(string Bsn, string Reference);

services/acl/Acl.Application/AclService.cs

@@ -2,12 +2,15 @@ namespace Acl.Application;
 
 /// <summary>The ACL's single operation: open a zaak from a domain payload,
 /// default-filling the ZGW-mandatory fields (ADR-0003).</summary>
-public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, IZaaktypeCatalog catalog, IClock clock)
+public sealed class AclService(IZaakGateway gateway, IDefaultFillStore fill, IZaaktypeCatalog catalog, IClock clock)
 {
     public async Task<Uri> OpenZaakAsync(DomainRegistration registration, CancellationToken ct = default)
     {
         ArgumentNullException.ThrowIfNull(registration);
 
+        // Read the current default-fill per zaak (not at construction), so a beheerder edit (S-15b)
+        // takes effect on the next zaak without a restart.
+        var defaults = fill.Current;
         var request = new ZaakRequest(
             defaults.Bronorganisatie,
             defaults.VerantwoordelijkeOrganisatie,
@@ -47,6 +50,17 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, IZaak
     public Task<IReadOnlyList<ZaaktypeSummary>> ListZaaktypenAsync(CancellationToken ct = default) =>
         gateway.ListZaaktypenAsync(ct);
 
+    /// <summary>The current default-fill settings, for the beheer config viewer (S-15b).</summary>
+    public DefaultFillSettings GetDefaultFill() => fill.Current;
+
+    /// <summary>Replace the default-fill settings from the beheer portal (S-15b). Takes effect on the
+    /// next zaak (the fill is read per zaak, not cached).</summary>
+    public void UpdateDefaultFill(DefaultFillSettings settings)
+    {
+        ArgumentNullException.ThrowIfNull(settings);
+        fill.Update(settings);
+    }
+
     /// <summary>The zaak's reference (its ZGW identificatie), for the read projection (#78).</summary>
     public Task<string> GetZaakReferenceAsync(Uri zaakUrl, CancellationToken ct = default)
     {
@@ -68,6 +82,7 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, IZaak
         ArgumentException.ThrowIfNullOrWhiteSpace(fileName);
         ArgumentException.ThrowIfNullOrWhiteSpace(contentType);
 
+        var defaults = fill.Current;
         var request = new DocumentRequest(
             defaults.Bronorganisatie,
             await catalog.GetInformatieobjecttypeUrlAsync(ct),

services/acl/Acl.Tests/AclServiceTests.cs

@@ -84,8 +84,11 @@ public class AclServiceTests
         InformatieobjecttypeOmschrijving = "Diploma",
     };
 
+    private static InMemoryDefaultFillStore FillFrom(AclDefaults d) =>
+        new(new DefaultFillSettings(d.Bronorganisatie, d.VerantwoordelijkeOrganisatie, d.Vertrouwelijkheidaanduiding));
+
     private static AclService ServiceWith(FakeGateway gateway, AclDefaults defaults, DateOnly today) =>
-        new(gateway, defaults, new CachedZaaktypeCatalog(gateway, defaults), new FixedClock(today));
+        new(gateway, FillFrom(defaults), new CachedZaaktypeCatalog(gateway, defaults), new FixedClock(today));
 
     private sealed class FixedClock(DateOnly today) : IClock
     {
@@ -113,6 +116,22 @@ public class AclServiceTests
         Assert.Equal("reg-77", req.Identificatie);
     }
 
+    [Fact]
+    public async Task Opening_a_zaak_reflects_a_default_fill_update(/* S-15b */)
+    {
+        var gateway = new FakeGateway();
+        var service = ServiceWith(gateway, Defaults(), new DateOnly(2026, 6, 4));
+
+        // A beheerder edits the default-fill; the very next zaak must use the new values (read per zaak).
+        service.UpdateDefaultFill(new DefaultFillSettings("999999999", "888888888", "vertrouwelijk"));
+        await service.OpenZaakAsync(new DomainRegistration("123456782", "reg-1"));
+
+        var req = gateway.Captured!;
+        Assert.Equal("999999999", req.Bronorganisatie);
+        Assert.Equal("888888888", req.VerantwoordelijkeOrganisatie);
+        Assert.Equal("vertrouwelijk", req.Vertrouwelijkheidaanduiding);
+    }
+
     [Fact]
     public async Task Rejects_a_null_registration_without_calling_the_gateway()
     {

tests/acceptance/Steps/EenZaakOpenenSteps.cs

@@ -44,7 +44,9 @@ public sealed class EenZaakOpenenSteps
     [When("the domain asks the ACL to open a zaak")]
     public async Task WhenTheDomainAsksTheAclToOpenAZaak()
     {
-        var service = new AclService(_gateway, _defaults!, new CachedZaaktypeCatalog(_gateway, _defaults!), new FixedClock(_today));
+        var fill = new InMemoryDefaultFillStore(new DefaultFillSettings(
+            _defaults!.Bronorganisatie, _defaults.VerantwoordelijkeOrganisatie, _defaults.Vertrouwelijkheidaanduiding));
+        var service = new AclService(_gateway, fill, new CachedZaaktypeCatalog(_gateway, _defaults!), new FixedClock(_today));
         _returnedUrl = await service.OpenZaakAsync(_registration!);
     }