feat: zitadel token auth middleware

server/utils/auth.ts

@@ -0,0 +1,59 @@
+import { createRemoteJWKSet, jwtVerify, type JWTPayload, type JWTVerifyGetKey } from "jose";
+
+type KeyInput = Parameters<typeof jwtVerify>[1];
+
+export interface VerifierConfig {
+  issuer: string;
+  /** Token is accepted if its `aud` includes at least one of these. */
+  audiences: string[];
+  /** Token `sub` must be one of these (the single owner). */
+  allowedSubs: string[];
+  /** Test seam: resolve the verification key directly instead of fetching JWKS. */
+  keyResolver?: (token: string) => Promise<KeyInput>;
+}
+
+/**
+ * Build a Zitadel access-token verifier. Verifies signature + issuer + expiry via JWKS,
+ * then enforces audience and owner-sub allowlists. Throws on any failure.
+ */
+export function makeVerifier(cfg: VerifierConfig) {
+  const jwks: JWTVerifyGetKey | null = cfg.keyResolver
+    ? null
+    : createRemoteJWKSet(new URL(`${cfg.issuer}/oauth/v2/keys`));
+
+  return async function verify(token: string): Promise<JWTPayload> {
+    const key: KeyInput = cfg.keyResolver ? await cfg.keyResolver(token) : (jwks as JWTVerifyGetKey);
+    const { payload } = await jwtVerify(token, key, { issuer: cfg.issuer });
+
+    const aud = Array.isArray(payload.aud) ? payload.aud : payload.aud ? [payload.aud] : [];
+    if (!cfg.audiences.some((a) => aud.includes(a))) {
+      throw new Error("token audience not accepted");
+    }
+    if (!cfg.allowedSubs.includes(String(payload.sub))) {
+      throw new Error("subject not allowed");
+    }
+    return payload;
+  };
+}
+
+function splitCsv(v: unknown): string[] {
+  return String(v ?? "")
+    .split(",")
+    .map((s) => s.trim())
+    .filter(Boolean);
+}
+
+let _cached: ReturnType<typeof makeVerifier> | null = null;
+
+/** Process-wide verifier built from runtime config (Nitro server context). */
+export function getVerifier() {
+  if (!_cached) {
+    const c = useRuntimeConfig();
+    _cached = makeVerifier({
+      issuer: c.zitadelIssuer,
+      audiences: splitCsv(c.zitadelAudience),
+      allowedSubs: splitCsv(c.allowedUserIds),
+    });
+  }
+  return _cached;
+}