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CORS Policy

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CORS Policy

This document describes the Cross-Origin Resource Sharing (CORS) policy enforced by the Bloqr Cloudflare Worker. It covers allowed origins, the preflight flow, no-origin requests, error responses, and Zero Trust integration.

Overview

All HTTP responses from the Worker include CORS headers computed at request time. The policy is strict by default:

  • Only origins listed in CORS_ALLOWED_ORIGINS (a Worker environment binding) receive a permissive Access-Control-Allow-Origin header.
  • Requests from unlisted origins are actively rejected with a 403 ProblemDetails (corsRejection) — the Worker does not silently omit the header.
  • Requests with no Origin header (direct server-to-server, CLI, or Postman) are allowed through unconditionally.
  • Preflight OPTIONS requests return the full policy headers and 204 No Content.

CORS Request Decision Flow

flowchart TD
    A[Incoming Request] --> B{Origin header present?}
    B -- No --> C[Allow: direct / server-to-server]
    B -- Yes --> D{Origin in\nCORS_ALLOWED_ORIGINS?}
    D -- Yes --> E[Set Access-Control-Allow-Origin\n= request Origin]
    D -- No --> F[Return 403 ProblemDetails\ncorsRejection]
    E --> G{Method = OPTIONS?}
    G -- Yes --> I[Return 204 with\npreflight headers]
    G -- No --> J[Continue to route handler\nwith CORS headers set]

Environment Binding

The allowed-origins list is configured via the CORS_ALLOWED_ORIGINS Worker binding (a comma-delimited string):

wrangler.toml
[vars]
CORS_ALLOWED_ORIGINS = "https://app.bloqr.app,https://admin.bloqr.app"

For local development, override via .dev.vars:

.dev.vars
CORS_ALLOWED_ORIGINS = "http://localhost:4200,http://localhost:4201"

Middleware Implementation

CORS is implemented in two steps inside worker/hono-app.ts:

Step 4 — Hono cors() middleware computes and attaches CORS response headers. For public endpoints (health, metrics, docs) it returns '*'; for all other endpoints it echoes the request Origin only when it matches the allowlist.

Step 4a — Origin enforcement middleware rejects disallowed origins with a 403 ProblemDetails response. Requests without an Origin header pass through unconditionally; public-endpoint requests also pass through.

// worker/hono-app.ts — Step 4: Hono cors() middleware
app.use(
    '*',
    cors({
        origin: (origin, c) => {
            const pathname = new URL(c.req.url).pathname;
            if (isPublicEndpoint(pathname)) return '*';
            return matchOrigin(origin, c.env as Env) ?? undefined;
        },
        allowMethods: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE', 'OPTIONS'],
        allowHeaders: [
            'Content-Type',
            'Authorization',
            'X-Turnstile-Token',
            'X-Payg-Session',
            'X-Payment-Response',
            'X-Stripe-Customer-Id',
        ],
        exposeHeaders: ['X-Payg-Session-Remaining', 'X-Payment-Required', 'X-Request-Id'],
        maxAge: 86400,
        credentials: true,
    }),
);


// worker/hono-app.ts — Step 4a: explicit origin enforcement
app.use('*', async (c, next) => {
    const origin = c.req.header('Origin');


    // No Origin header → non-browser client → allow through unconditionally.
    if (!origin) {
        await next();
        return;
    }


    const pathname = c.req.path;


    // Public endpoints allow any origin (wildcard * returned by step 4).
    if (isPublicEndpoint(pathname)) {
        await next();
        return;
    }


    const allowed = matchOrigin(origin, c.env as Env);
    if (!allowed) {
        analytics?.trackSecurityEvent({ eventType: 'cors_rejection', ... });
        return ProblemResponse.corsRejection(pathname, `Origin '${origin}' is not permitted.`);
    }


    await next();
});

The matchOrigin helper (in worker/utils/cors.ts) checks the request Origin against the comma-delimited CORS_ALLOWED_ORIGINS Worker binding.

Preflight OPTIONS Response Headers

A complete preflight response for an allowed origin:

HTTP/1.1 204 No Content
Access-Control-Allow-Origin: https://app.bloqr.app
Access-Control-Allow-Methods: GET, POST, PUT, PATCH, DELETE, OPTIONS
Access-Control-Allow-Headers: Content-Type, Authorization, X-Turnstile-Token, X-Payg-Session, X-Payment-Response, X-Stripe-Customer-Id
Access-Control-Expose-Headers: X-Payg-Session-Remaining, X-Payment-Required, X-Request-Id
Access-Control-Allow-Credentials: true
Access-Control-Max-Age: 86400
Vary: Origin

X-Turnstile-Token is retained in Access-Control-Allow-Headers for backward compatibility with older callers. The Angular frontend now injects the Turnstile token into the JSON request body (turnstileToken field) rather than as a header — see Turnstile Middleware for the current implementation.

No-Origin Requests

Requests without an Origin header — typically from:

  • cURL / Postman / Newman (API testing)
  • Server-to-server calls (CI pipeline, Worker-to-Worker)
  • Cloudflare Cron Triggers

…are allowed through without any CORS header manipulation. The route handler processes them normally. No CORS headers are added to the response for these requests; this is intentional and correct.

Security note (ZTA): Absence of an Origin header does not bypass authentication. All endpoints that require a session still invoke auth.api.getSession(). CORS is a browser enforcement mechanism — it does not substitute for server-side access control.

Error Responses

When a request arrives from a disallowed origin (i.e., the Origin header is present but not in CORS_ALLOWED_ORIGINS), the Worker returns a 403 Forbidden response with a ProblemDetails JSON body (ProblemResponse.corsRejection). The request is terminated — it does not proceed to the route handler.

For preflight (OPTIONS) requests from disallowed origins, the Worker likewise returns a 403 with no Access-Control-Allow-Origin header. The browser will not proceed with the actual request.

Adding a New Allowed Origin

  1. Update CORS_ALLOWED_ORIGINS in wrangler.toml (for production) or .dev.vars (for local dev).
  2. If the origin is on a new subdomain of bloqr.app, ensure the better-auth trustedOrigins binding (TRUSTED_ORIGINS) also includes it — see Better Auth Security Audit, AUDIT-11.
  3. If the origin requires cookie sharing, verify the session cookie Domain attribute is set to .bloqr.app.

Zero Trust Integration

ZTA PrincipleCORS Implementation
Verify explicitlyEvery request from a browser origin is checked against the explicit allow-list
Least privilegeAccess-Control-Allow-Origin is echoed only for approved origins
Never trust, always verifyCredentials (Authorization, session cookie) are still validated server-side regardless of CORS outcome
Short-lived accessAccess-Control-Max-Age: 86400 caps preflight caching at 24 hours