w4c-workflows-api/Middleware/AuthMiddleware.cs

using w4c_workflows.Services;

namespace w4c_workflows.Middleware;

/// <summary>
/// Two auth surfaces for the control plane:
///   - /api/keys*  → the tenant's main JWT (shared Auth:JwtSigningKey). Lets a
///     logged-in tenant mint/rotate/revoke its operator keys.
///   - everything else → per-tenant operator key (Authorization: Bearer <key>).
///     Used by both the frontend and the per-tenant worker.
/// Resolved identity is exposed via HttpContext.Items: TenantId, Scopes,
/// AuthKind ("jwt" | "operator").
/// </summary>
public class AuthMiddleware
{
    private static readonly PathString[] PublicPaths =
    {
        new("/health"),
        new("/health/ready"),
        new("/openapi"),
        new("/scalar"), // interactive API explorer (Scalar) — no operator key needed
        new("/api/scalar"), // Scalar reference exposed under /api/scalar/<svc> — no operator key needed
        new("/h"), // webhook receiver (external callers have no operator key)
    };

    private readonly RequestDelegate _next;
    private readonly string _signingKey;
    private readonly ILogger<AuthMiddleware> _logger;

    public AuthMiddleware(RequestDelegate next, IConfiguration config, ILogger<AuthMiddleware> logger)
    {
        _next = next;
        _signingKey = config["Auth:JwtSigningKey"] ?? string.Empty;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var path = context.Request.Path;

        if (IsPublic(path))
        {
            await _next(context);
            return;
        }

        // /api/keys* — main JWT surface.
        if (path.StartsWithSegments("/api/keys"))
        {
            var principal = JwtValidator.Validate(context.Request.Headers.Authorization.ToString(), _signingKey);
            var tenantId = principal?.FindFirst("tenant_id")?.Value;
            if (principal == null || string.IsNullOrEmpty(tenantId))
            {
                await Unauthorized(context, "Valid main JWT required for key management");
                return;
            }

            context.Items["TenantId"] = tenantId;
            context.Items["AuthKind"] = "jwt";
            await _next(context);
            return;
        }

        // The rich HTML preview endpoint (/api/workflows/{id}/html) is reached
        // from an <iframe>, which cannot send the operator-key Authorization
        // header. It therefore accepts a short-lived signed token in ?token= —
        // minted by /html-token with the operator key. Without a token it falls
        // through to the normal operator-key check below (API use).
        if (IsHtmlRenderPath(path))
        {
            var token = context.Request.Query["token"].ToString();
            if (!string.IsNullOrEmpty(token))
            {
                var renderTokens = context.RequestServices.GetRequiredService<RenderTokenService>();
                if (renderTokens.TryVerify(token, out var tenantId, out var workflowId))
                {
                    context.Items["TenantId"] = tenantId;
                    context.Items["AuthKind"] = "render-token";
                    context.Items["RenderWorkflowId"] = workflowId;
                    await _next(context);
                    return;
                }
                // A token was supplied but is invalid/expired — fail rather than
                // silently falling through to the header check.
                await Unauthorized(context, "Invalid or expired render token");
                return;
            }
        }

        // Everything else — operator key surface.
        var services = context.RequestServices;
        var keys = services.GetRequiredService<ApiKeyService>();
        var op = await keys.VerifyAsync(context.Request.Headers.Authorization.ToString(), context.RequestAborted);
        if (op == null)
        {
            await Unauthorized(context, "Valid operator key required");
            return;
        }

        context.Items["TenantId"] = op.TenantId;
        context.Items["AuthKind"] = "operator";
        context.Items["Scopes"] = op.Scopes;
        context.Items["OperatorKeyId"] = op.KeyId;
        _logger.LogDebug("Operator-key auth for tenant {TenantId}", op.TenantId);

        await _next(context);
    }

    private static bool IsPublic(PathString path)
    {
        foreach (var publicPath in PublicPaths)
        {
            if (path.StartsWithSegments(publicPath))
                return true;
        }
        return false;
    }

    /// <summary>
    /// Matches the backend HTML render route: <c>/api/workflows/{guid}/html</c>.
    /// Exactly five segments ("" + api/workflows/{id}/html) with an html tail.
    /// </summary>
    private static bool IsHtmlRenderPath(PathString path)
    {
        var value = path.Value;
        if (string.IsNullOrEmpty(value)) return false;
        var segments = value.Split('/', StringSplitOptions.RemoveEmptyEntries);
        return segments.Length == 4
            && segments[0] == "api"
            && segments[1] == "workflows"
            && segments[3] == "html";
    }

    private static Task Unauthorized(HttpContext context, string message)
    {
        context.Response.StatusCode = StatusCodes.Status401Unauthorized;
        context.Response.ContentType = "application/json";
        return context.Response.WriteAsync($"{{\"error\":\"{message}\"}}");
    }
}