config-loader: reject configs with keys adjacent to secret keys

packages/config-loader/src/lib/reader.test.ts

@@ -106,6 +106,24 @@ describe('readConfigFile', () => {
     });
   });
 
+  it('should not allow keys adjacent to secrets', async () => {
+    const readFile = memoryFiles({
+      './app-config.yaml': 'app: { extraKey: 3, $file: "./my-secret" }',
+    });
+    const readSecret = jest.fn().mockResolvedValue('secret');
+
+    const config = readConfigFile('./app-config.yaml', {
+      ...mockContext,
+      readFile,
+      readSecret: readSecret as ReadSecretFunc,
+    });
+
+    await expect(config).rejects.toThrow(
+      "Secret key '$file' has adjacent keys at .app",
+    );
+    expect(readSecret).not.toHaveBeenCalled();
+  });
+
   it('should read deprecated secrets', async () => {
     const readFile = memoryFiles({
       './app-config.yaml': 'app: { $secret: { file: "./my-secret" } }',

packages/config-loader/src/lib/reader.ts

@@ -74,8 +74,15 @@ export async function readConfigFile(
       }
     }
 
+    // Check if there's any key that starts with a '$', in that case we treat
+    // this entire object as a secret.
     const [secretKey] = Object.keys(obj).filter(key => key.startsWith('$'));
     if (secretKey) {
+      if (Object.keys(obj).length !== 1) {
+        throw new Error(
+          `Secret key '${secretKey}' has adjacent keys at ${path}`,
+        );
+      }
       try {
         return await ctx.readSecret(path, {
           [secretKey.slice(1)]: obj[secretKey],