services/acl/Acl.Api/Program.cs

@@ -24,8 +24,18 @@ app.MapPost("/zaken", async (OpenZaakRequest body, AclService acl, CancellationT
     return Results.Ok(new { zaakUrl = zaakUrl.ToString() });
 });
 
+// Approve a zaak: set it to its zaaktype's eindstatus (S-09b). The domain hands over only the zaak
+// URL; the ACL owns the ZGW statustype resolution (§8.1).
+app.MapPost("/statussen", async (SetStatusRequest body, AclService acl, CancellationToken ct) =>
+{
+    await acl.ApproveZaakAsync(new Uri(body.ZaakUrl), ct);
+    return Results.NoContent();
+});
+
 app.Run();
 
 public sealed record OpenZaakRequest(string Bsn);
 
+public sealed record SetStatusRequest(string ZaakUrl);
+
 public partial class Program;

services/acl/Acl.Application/AclService.cs

@@ -17,4 +17,15 @@ public sealed class AclService(IZaakGateway gateway, AclDefaults defaults, ICloc
 
         return gateway.OpenZaakAsync(request, ct);
     }
+
+    /// <summary>
+    /// Approve a zaak: set it to the eindstatus of the configured BIG zaaktype (ADR-0003 default). The
+    /// domain hands over only the zaak URL; the ACL owns which statustype means "approved" (§8.1).
+    /// </summary>
+    public Task ApproveZaakAsync(Uri zaakUrl, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+
+        return gateway.SetZaakToEindstatusAsync(zaakUrl, defaults.ZaaktypeUrl, clock.Today, ct);
+    }
 }

services/acl/Acl.Application/IZaakGateway.cs

@@ -5,4 +5,11 @@ namespace Acl.Application;
 public interface IZaakGateway
 {
     Task<Uri> OpenZaakAsync(ZaakRequest request, CancellationToken ct = default);
+
+    /// <summary>
+    /// Set the given zaak to the <em>eindstatus</em> (final statustype) of the supplied zaaktype —
+    /// the ZGW translation of "approve". The gateway resolves which statustype is the eindstatus from
+    /// the catalogus and POSTs a status against the zaak, dated <paramref name="datumStatusGezet"/>.
+    /// </summary>
+    Task SetZaakToEindstatusAsync(Uri zaakUrl, Uri zaaktypeUrl, DateOnly datumStatusGezet, CancellationToken ct = default);
 }

services/acl/Acl.Infrastructure/OpenZaakGateway.cs

@@ -41,6 +41,56 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
         return new Uri(created.Url);
     }
 
+    public async Task SetZaakToEindstatusAsync(Uri zaakUrl, Uri zaaktypeUrl, DateOnly datumStatusGezet, CancellationToken ct = default)
+    {
+        ArgumentNullException.ThrowIfNull(zaakUrl);
+        ArgumentNullException.ThrowIfNull(zaaktypeUrl);
+
+        var eindstatus = await ResolveEindstatusAsync(zaaktypeUrl, ct);
+
+        using var message = new HttpRequestMessage(
+            HttpMethod.Post, new Uri(options.BaseUrl, "/zaken/api/v1/statussen"))
+        {
+            Content = JsonContent.Create(new StatusDto(
+                zaakUrl.ToString(),
+                eindstatus.ToString(),
+                // datumStatusGezet is a ZGW date-time; set it at the start of the given day (UTC).
+                datumStatusGezet.ToDateTime(TimeOnly.MinValue, DateTimeKind.Utc).ToString("yyyy-MM-ddTHH:mm:ssZ"))),
+        };
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+        // The status resource carries no geometry, so no CRS headers. As with zaak-create, buffer the
+        // body so uwsgi gets a Content-Length instead of a chunked body.
+        await message.Content.LoadIntoBufferAsync(ct);
+
+        using var response = await http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+    }
+
+    /// <summary>Resolve the zaaktype's eindstatus (the terminal statustype) from the catalogus.</summary>
+    private async Task<Uri> ResolveEindstatusAsync(Uri zaaktypeUrl, CancellationToken ct)
+    {
+        var query = new Uri(options.BaseUrl,
+            "/catalogi/api/v1/statustypen?status=alles&zaaktype=" + Uri.EscapeDataString(zaaktypeUrl.ToString()));
+        using var message = new HttpRequestMessage(HttpMethod.Get, query);
+        message.Headers.Authorization =
+            new AuthenticationHeaderValue("Bearer", ZgwToken.Mint(options.ClientId, options.Secret));
+
+        using var response = await http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+
+        var page = await response.Content.ReadFromJsonAsync<StatustypePage>(ct)
+            ?? throw new InvalidOperationException("OpenZaak returned an empty statustypen response");
+        var results = page.Results ?? [];
+
+        // OpenZaak flags the terminal statustype (highest volgnummer) as isEindstatus; fall back to the
+        // highest volgnummer if the flag is absent.
+        var eindstatus = results.FirstOrDefault(s => s.IsEindstatus)
+            ?? results.OrderByDescending(s => s.Volgnummer).FirstOrDefault()
+            ?? throw new InvalidOperationException($"No statustypen found for zaaktype {zaaktypeUrl}");
+        return new Uri(eindstatus.Url);
+    }
+
     private sealed record ZaakDto(
         [property: JsonPropertyName("bronorganisatie")] string Bronorganisatie,
         [property: JsonPropertyName("zaaktype")] string Zaaktype,
@@ -50,4 +100,17 @@ public sealed class OpenZaakGateway(HttpClient http, OpenZaakOptions options) :
 
     private sealed record ZaakCreatedDto(
         [property: JsonPropertyName("url")] string Url);
+
+    private sealed record StatusDto(
+        [property: JsonPropertyName("zaak")] string Zaak,
+        [property: JsonPropertyName("statustype")] string Statustype,
+        [property: JsonPropertyName("datumStatusGezet")] string DatumStatusGezet);
+
+    private sealed record StatustypePage(
+        [property: JsonPropertyName("results")] IReadOnlyList<StatustypeDto>? Results);
+
+    private sealed record StatustypeDto(
+        [property: JsonPropertyName("url")] string Url,
+        [property: JsonPropertyName("volgnummer")] int Volgnummer,
+        [property: JsonPropertyName("isEindstatus")] bool IsEindstatus);
 }

services/acl/Acl.IntegrationTests/OpenZaakFixture.cs

@@ -65,6 +65,43 @@ public sealed class OpenZaakFixture : IDisposable
         return JsonDocument.Parse(json).RootElement.Clone();
     }
 
+    /// <summary>GETs a non-geo ZGW resource (e.g. a status) by URL — no CRS headers.</summary>
+    public async Task<JsonElement> GetJsonAsync(Uri url, CancellationToken ct = default)
+    {
+        using var message = new HttpRequestMessage(HttpMethod.Get, url);
+        message.Headers.Authorization = new AuthenticationHeaderValue("Bearer", MintToken());
+
+        using var response = await Http.SendAsync(message, ct);
+        response.EnsureSuccessStatusCode();
+        var json = await response.Content.ReadAsStringAsync(ct);
+        return JsonDocument.Parse(json).RootElement.Clone();
+    }
+
+    /// <summary>The zaaktype's eindstatus (terminal statustype) URL — the one an approval sets.</summary>
+    public async Task<Uri> FindEindstatustypeAsync(Uri zaaktypeUrl, CancellationToken ct = default)
+    {
+        var query = new Uri(BaseUrl,
+            "/catalogi/api/v1/statustypen?status=alles&zaaktype=" + Uri.EscapeDataString(zaaktypeUrl.ToString()));
+        var page = await GetJsonAsync(query, ct);
+        var results = page.GetProperty("results");
+
+        Uri? fallback = null;
+        var highest = int.MinValue;
+        foreach (var st in results.EnumerateArray())
+        {
+            if (st.TryGetProperty("isEindstatus", out var eind) && eind.GetBoolean())
+                return new Uri(st.GetProperty("url").GetString()!);
+            var volgnummer = st.GetProperty("volgnummer").GetInt32();
+            if (volgnummer > highest)
+            {
+                highest = volgnummer;
+                fallback = new Uri(st.GetProperty("url").GetString()!);
+            }
+        }
+
+        return fallback ?? throw new InvalidOperationException($"No statustypen for zaaktype {zaaktypeUrl}");
+    }
+
     // A ZGW (vng-api-common) HS256 JWT, mirroring the seed's client. Minted here
     // rather than reusing Acl.Infrastructure's internal minter to keep that internal.
     private string MintToken()

services/acl/Acl.IntegrationTests/OpenZaakGatewayIntegrationTests.cs

@@ -42,4 +42,32 @@ public sealed class OpenZaakGatewayIntegrationTests(OpenZaakFixture stack)
         Assert.Equal("517439943", zaak.GetProperty("bronorganisatie").GetString());
         Assert.Equal("openbaar", zaak.GetProperty("vertrouwelijkheidaanduiding").GetString());
     }
+
+    [Fact]
+    public async Task Setting_a_zaak_to_its_eindstatus_records_the_terminal_statustype()
+    {
+        var zaaktype = await stack.FindPublishedBigZaaktypeAsync();
+        Assert.True(zaaktype is not null,
+            "No published BIG-REGISTRATIE zaaktype found in OpenZaak — bring the stack up and " +
+            "seed it with OZ_PUBLISH=1 (`make integration` does this).");
+
+        var gateway = new OpenZaakGateway(stack.Http, stack.Options);
+        var zaakUrl = await gateway.OpenZaakAsync(new ZaakRequest(
+            Bronorganisatie: "517439943",
+            VerantwoordelijkeOrganisatie: "517439943",
+            Vertrouwelijkheidaanduiding: "openbaar",
+            Zaaktype: zaaktype!,
+            Startdatum: DateOnly.FromDateTime(DateTime.UtcNow)));
+
+        await gateway.SetZaakToEindstatusAsync(zaakUrl, zaaktype!, DateOnly.FromDateTime(DateTime.UtcNow));
+
+        // The zaak now carries a current status, and it is the zaaktype's eindstatus.
+        var zaak = await stack.GetZaakAsync(zaakUrl);
+        var statusUrl = zaak.GetProperty("status").GetString();
+        Assert.False(string.IsNullOrEmpty(statusUrl), "the approved zaak has no current status");
+
+        var status = await stack.GetJsonAsync(new Uri(statusUrl!));
+        var eindstatustype = await stack.FindEindstatustypeAsync(zaaktype!);
+        Assert.Equal(eindstatustype.ToString(), status.GetProperty("statustype").GetString());
+    }
 }