blog-zig-mongo/extras/auth-clerk

Auth via Clerk

clerk.zig replaces the local email+password auth with Clerk: the app stops issuing tokens and instead verifies Clerk session JWTs (RS256) against your instance's JWKS — signature, exp and nbf — using only the standard library.

Setup

1. Copy clerk.zig into src/ and delete src/jwt.zig.

2. src/auth.zig shrinks to requireAuth (drop register, login, normalizeEmail and the argon2/jwt imports):

   pub fn requireAuth(app: *App, arena: Allocator, req: *http.Server.Request) ![]const u8 {
       const token = web.bearerToken(req) orelse return error.Unauthorized;
       return app.verifier.verify(arena, token) catch error.Unauthorized;
   }
   

3. In src/main.zig, remove the /auth/register and /auth/login routes, add const clerk = @import("clerk.zig");, replace the auth_secret field of App with verifier: *clerk.Verifier, and replace the AUTH_SECRET lookup in main with:

   const jwks_url = env.get("CLERK_JWKS_URL") orelse
       std.process.fatal("CLERK_JWKS_URL is required", .{});
   var verifier = clerk.Verifier.init(gpa, io, jwks_url);
   defer verifier.deinit();
   

   and set .verifier = &verifier where app is built.

4. Clerk user ids are strings (user_...), not ObjectIds, and Clerk is the user store now. In src/db.zig, store author_id as a string: in createPost drop the author ObjectId and append it with appendStr(doc, "author_id", author_id), and read it with getStr(arena, doc, "author_id") in parsePost. Delete User, createUser, getUserByEmail and the users index in ensureIndexes. src/posts.zig already treats user ids as strings.

5. Set CLERK_JWKS_URL=https://<your-instance>.clerk.accounts.dev/.well-known/jwks.json (Clerk dashboard → API keys) instead of AUTH_SECRET.

Clients send the Clerk session token as Authorization: Bearer <token> (await session.getToken() in Clerk's frontend SDKs).

Notes

• The JWKS is fetched over HTTPS with std.http.Client, which needs the system CA bundle — the runtime image installs ca-certificates.
• Keys are cached in memory. A token with an unknown kid triggers a refetch (at most once a minute), so key rotations need no restart.
• Clerk also puts the requesting origin in the azp claim; if browsers from other sites could hold your users' tokens, parse azp in verify and compare it with your frontend's origin.