Supabase static keys - simplified config (#140)

* Add simplified Supabase static key config.

* Use a separate config field for Supabase JWT keys.

* Add changeset.

---------

Co-authored-by: stevensJourney <[email protected]>

Author: rkistner

.changeset/green-forks-approve.md

@@ -0,0 +1,7 @@
+---
+'@powersync/service-core': minor
+'@powersync/service-types': minor
+'@powersync/service-image': minor
+---
+
+Add "supabase_jwt_secret" config option to simplify static Supabase auth.

modules/module-postgres/src/auth/SupabaseKeyCollector.ts

@@ -10,6 +10,8 @@ import * as pgwire_utils from '../utils/pgwire_utils.js';
  *
  * Unfortunately, despite the JWTs containing a kid, we have no way to lookup that kid
  * before receiving a valid token.
+ *
+ * @deprecated Supabase is removing support for "app.settings.jwt_secret".
  */
 export class SupabaseKeyCollector implements auth.KeyCollector {
   private pool: pgwire.PgClient;

packages/service-core/src/auth/StaticSupabaseKeyCollector.ts

@@ -0,0 +1,31 @@
+import * as jose from 'jose';
+import { KeySpec, KeyOptions } from './KeySpec.js';
+import { KeyCollector, KeyResult } from './KeyCollector.js';
+
+const SUPABASE_KEY_OPTIONS: KeyOptions = {
+  requiresAudience: ['authenticated'],
+  maxLifetimeSeconds: 86400 * 7 + 1200 // 1 week + 20 minutes margin
+};
+
+/**
+ * Set of static keys for Supabase.
+ *
+ * Same as StaticKeyCollector, but with some configuration tweaks for Supabase.
+ *
+ * Similar to SupabaseKeyCollector, but using hardcoded keys instead of fetching
+ * from the database.
+ *
+ * A key can be added both with and without a kid, in case wildcard matching is desired.
+ */
+export class StaticSupabaseKeyCollector implements KeyCollector {
+  static async importKeys(keys: jose.JWK[]) {
+    const parsedKeys = await Promise.all(keys.map((key) => KeySpec.importKey(key, SUPABASE_KEY_OPTIONS)));
+    return new StaticSupabaseKeyCollector(parsedKeys);
+  }
+
+  constructor(private keys: KeySpec[]) {}
+
+  async getKeys(): Promise<KeyResult> {
+    return { keys: this.keys, errors: [] };
+  }
+}

packages/service-core/src/auth/auth-index.ts

@@ -7,3 +7,4 @@ export * from './KeyStore.js';
 export * from './LeakyBucket.js';
 export * from './RemoteJWKSCollector.js';
 export * from './StaticKeyCollector.js';
+export * from './StaticSupabaseKeyCollector.js';

packages/service-core/src/util/config/compound-config-collector.ts

@@ -65,9 +65,27 @@ export class CompoundConfigCollector {
 
     const inputKeys = baseConfig.client_auth?.jwks?.keys ?? [];
     const staticCollector = await auth.StaticKeyCollector.importKeys(inputKeys);
-
     collectors.add(staticCollector);
 
+    if (baseConfig.client_auth?.supabase && baseConfig.client_auth?.supabase_jwt_secret != null) {
+      // This replaces the old SupabaseKeyCollector, with a statically-configured key.
+      // You can get the same effect with manual HS256 key configuration, but this
+      // makes the config simpler.
+      // We also a custom audience ("authenticated"), increased max lifetime (1 week),
+      // and auto base64-url-encode the key.
+      collectors.add(
+        await auth.StaticSupabaseKeyCollector.importKeys([
+          {
+            kty: 'oct',
+            alg: 'HS256',
+            // In this case, the key is not base64-encoded yet.
+            k: Buffer.from(baseConfig.client_auth.supabase_jwt_secret, 'utf8').toString('base64url'),
+            kid: undefined // Wildcard kid - any kid can match
+          }
+        ])
+      );
+    }
+
     let jwks_uris = baseConfig.client_auth?.jwks_uri ?? [];
     if (typeof jwks_uris == 'string') {
       jwks_uris = [jwks_uris];

packages/types/src/config/PowerSyncConfig.ts

@@ -115,6 +115,7 @@ export const powerSyncConfig = t.object({
       block_local_jwks: t.boolean.optional(),
       jwks: strictJwks.optional(),
       supabase: t.boolean.optional(),
+      supabase_jwt_secret: t.string.optional(),
       audience: t.array(t.string).optional()
     })
     .optional(),