register-referentie/services/bff/Bff.Api/Program.cs

using System.Security.Claims;
using System.Text.Json;
using System.Text.Json.Serialization;
using Bff.Api;
using Microsoft.AspNetCore.Authentication.JwtBearer;

var builder = WebApplication.CreateBuilder(args);

var keycloakAuthority = builder.Configuration["Keycloak:Authority"]
    ?? throw new InvalidOperationException("Missing configuration 'Keycloak:Authority'");
// Behandelaars authenticate against a *different* Keycloak realm (medewerker) than citizens (digid),
// so the BFF validates a second issuer for the behandel endpoints (ADR-0013).
var medewerkerAuthority = builder.Configuration["Keycloak:MedewerkerAuthority"]
    ?? throw new InvalidOperationException("Missing configuration 'Keycloak:MedewerkerAuthority'");
var domainBaseUrl = builder.Configuration["Downstream:Domain:BaseUrl"]
    ?? throw new InvalidOperationException("Missing configuration 'Downstream:Domain:BaseUrl'");
var projectionBaseUrl = builder.Configuration["Downstream:Projection:BaseUrl"]
    ?? throw new InvalidOperationException("Missing configuration 'Downstream:Projection:BaseUrl'");

// Validate Keycloak-issued tokens (ADR-0010). Audience validation is off for the walking skeleton —
// Keycloak's audience mapping is a later hardening; signature/issuer/expiry are validated.
builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.Authority = keycloakAuthority;
        options.RequireHttpsMetadata = false;
        options.TokenValidationParameters.ValidateAudience = false;
    })
    // The medewerker realm — behandel endpoints only. On validation we lift Keycloak's realm roles
    // (the nested realm_access.roles claim) into role claims so authorization policies can require them.
    .AddJwtBearer(BehandelAuth.Scheme, options =>
    {
        options.Authority = medewerkerAuthority;
        options.RequireHttpsMetadata = false;
        options.TokenValidationParameters.ValidateAudience = false;
        options.Events = new JwtBearerEvents
        {
            OnTokenValidated = context =>
            {
                BehandelAuth.AddRealmRoles(context.Principal);
                return Task.CompletedTask;
            },
        };
    });
builder.Services.AddAuthorization(options =>
    options.AddPolicy(BehandelAuth.Policy, policy => policy
        .AddAuthenticationSchemes(BehandelAuth.Scheme)
        .RequireAuthenticatedUser()
        .RequireRole(BehandelAuth.BehandelaarRole)));

// The BFF is the portals' only backend; it fans out to the domain and projection (§8.3).
builder.Services.AddHttpClient<IDomainClient, DomainClient>(c => c.BaseAddress = new Uri(domainBaseUrl));
builder.Services.AddHttpClient<IProjectionClient, ProjectionClient>(c => c.BaseAddress = new Uri(projectionBaseUrl));

builder.Services.AddHealthChecks();
// Clear the auto-populated `servers` block so the committed spec is stable regardless of the host
// the doc was generated from (the client sets its own base URL). Keeps the drift guard deterministic.
builder.Services.AddOpenApi(options =>
    options.AddDocumentTransformer((document, _, _) =>
    {
        document.Servers?.Clear();
        return Task.CompletedTask;
    }));

var app = builder.Build();

app.UseAuthentication();
app.UseAuthorization();

app.MapHealthChecks("/health");
app.MapOpenApi();

// Self-service submit: requires a valid digid token; the bsn comes from the token, not the body,
// and is forwarded to the domain (ADR-0010). Returns 202 — the zaak is opened asynchronously (S-05).
app.MapPost("/self-service/registrations", async (ClaimsPrincipal user, IDomainClient domain, CancellationToken ct) =>
{
    var bsn = user.FindFirstValue("bsn");
    if (string.IsNullOrWhiteSpace(bsn))
        return Results.BadRequest("The token carries no bsn claim.");

    var accepted = await domain.SubmitRegistrationAsync(bsn, ct);
    return Results.Accepted($"/self-service/registrations/{accepted.RegistrationId}", accepted);
})
    .RequireAuthorization()
    .Produces<SubmitAccepted>(StatusCodes.Status202Accepted)
    .Produces(StatusCodes.Status400BadRequest)
    .Produces(StatusCodes.Status401Unauthorized);

// Openbaar register: an anonymous public lookup that exposes only public-safe fields (S-09).
app.MapGet("/openbaar/register", async (string? q, IProjectionClient projection, CancellationToken ct) =>
{
    var entries = await projection.GetRegisterAsync(ct);
    return Results.Ok(OpenbaarProjection.PublicView(entries, q));
})
    .Produces<IReadOnlyList<OpenbaarEntry>>(StatusCodes.Status200OK);

// Behandelaar's werkbak: registrations awaiting beoordeling. Reached only with a medewerker-realm
// token carrying the behandelaar role; the BFF proxies the domain's werkbak (staff view, ADR-0013).
app.MapGet("/behandel/werkbak", async (IDomainClient domain, CancellationToken ct) =>
    Results.Ok(await domain.GetWerkbakAsync(ct)))
    .RequireAuthorization(BehandelAuth.Policy)
    .Produces<IReadOnlyList<WerkbakItem>>(StatusCodes.Status200OK)
    .Produces(StatusCodes.Status401Unauthorized)
    .Produces(StatusCodes.Status403Forbidden);

app.Run();

// Behandel (medewerker-realm) authentication + authorization wiring (ADR-0013).
internal static class BehandelAuth
{
    public const string Scheme = "medewerker";
    public const string Policy = "behandelaar";
    public const string BehandelaarRole = "behandelaar";

    /// <summary>Lift Keycloak's realm roles (the nested <c>realm_access.roles</c> claim) onto the
    /// principal as role claims, so <c>RequireRole</c> can authorize on them.</summary>
    public static void AddRealmRoles(ClaimsPrincipal? principal)
    {
        if (principal?.Identity is not ClaimsIdentity identity)
            return;

        var realmAccess = principal.FindFirst("realm_access")?.Value;
        if (string.IsNullOrWhiteSpace(realmAccess))
            return;

        // A malformed realm_access claim must not fail authentication (a throw here becomes a 401);
        // it simply yields no roles, so the authorization policy answers 403.
        string[] roles;
        try
        {
            roles = JsonSerializer.Deserialize<RealmAccess>(realmAccess)?.Roles ?? [];
        }
        catch (JsonException)
        {
            return;
        }

        foreach (var role in roles)
            identity.AddClaim(new Claim(identity.RoleClaimType, role));
    }

    private sealed record RealmAccess([property: JsonPropertyName("roles")] string[] Roles);
}

// Exposed so the test host (WebApplicationFactory<Program>) can boot the app.
public partial class Program;