fix(github): check the private key before generating app tokens

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

bootstrap/helpers/github.php

@@ -166,11 +166,20 @@ function assertGithubClockInSync(string $apiUrl): void
     }
 }
 
+function githubAppPrivateKey(GithubApp $source): ?PrivateKey
+{
+    $privateKey = $source->privateKey;
+
+    return $privateKey?->team_id === $source->team_id ? $privateKey : null;
+}
+
 function generateGithubToken(GithubApp $source, string $type)
 {
+    $privateKey = githubAppPrivateKey($source) ?? throw new RuntimeException('Private key not found for this GitHub App.');
+
     assertGithubClockInSync($source->api_url);
 
-    $signingKey = InMemory::plainText($source->privateKey->private_key);
+    $signingKey = InMemory::plainText($privateKey->private_key);
     $algorithm = new Sha256;
     $tokenBuilder = (new Builder(new JoseEncoder, ChainedFormatter::default()));
     $now = CarbonImmutable::now()->setTimezone('UTC');
@@ -279,7 +288,7 @@ function syncGithubAppName(GithubApp $source, bool $throw = false): ?string
             return null;
         }
 
-        $privateKey = $source->privateKey ?: PrivateKey::find($source->private_key_id);
+        $privateKey = githubAppPrivateKey($source);
 
         if (! $privateKey) {
             return null;

tests/Feature/Application/GithubSourceChangeTest.php

@@ -278,6 +278,37 @@ describe('GitHub Source Change Component', function () {
         expect($githubApp->refresh()->private_key_id)->toBe($ownKey->id);
     })->with(['submit', 'instantSave']);
 
+    test('github app tokens only use a key from the source team', function () {
+        Http::fake();
+
+        $otherTeam = Team::factory()->create();
+        $foreignKey = PrivateKey::create([
+            'name' => 'other-team-key',
+            'private_key' => validPrivateKey(),
+            'team_id' => $otherTeam->id,
+        ]);
+
+        $githubApp = GithubApp::create([
+            'name' => 'Test GitHub App',
+            'api_url' => 'https://api.github.com',
+            'html_url' => 'https://github.com',
+            'custom_user' => 'git',
+            'custom_port' => 22,
+            'app_id' => 12345,
+            'installation_id' => 67890,
+            'team_id' => $this->team->id,
+            'is_system_wide' => false,
+        ]);
+        GithubApp::query()->whereKey($githubApp->id)->update(['private_key_id' => $foreignKey->id]);
+        $githubApp->refresh();
+
+        expect(fn () => generateGithubJwt($githubApp))->toThrow(RuntimeException::class)
+            ->and(syncGithubAppName($githubApp))->toBeNull()
+            ->and($foreignKey->refresh()->name)->toBe('other-team-key');
+
+        Http::assertNothingSent();
+    });
+
     test('ghe.com installation path encodes the organization segment', function () {
         $githubApp = new GithubApp;
         $githubApp->forceFill([