Amplify Hub not firing on `auth` events. when running from Custom Domain

Question

I have a custom domain purchased with Route 53.  My Amplify app has hosting configured to use it in production.
I can successfully login to my application from the backend https://prod.appID.amplifyapp.com/ domain. 
However, when I login attempt to login to https://myCustomDomain.org/ the Amplify Hub listener events never fire.

My app is configured like soo.

**App.tsx** snippet: 
```

Amplify.configure(updatedAwsConfig); //aws.exports is updated to correctly set oath.redirectSignIn and oauth.redirectSignOut (per AWS docs)
console.log(`Setting Updated Oauth: ${JSON.stringify(updatedAwsConfig.oauth)}`);

Hub.listen('auth', authEventsProcessor);

function App() 
{ 
    //main app page is defined here.
```

**authEventsProcessor** definition
```
export const authEventsProcessor = (data: any) : HubCallback | LegacyCallback => {
//any => {
   console.log(`Processing Auth Event:
${JSON.stringify(data)}`);
   //console.log(`Processing Auth Event(2):
 ${data}`);
   switch (data.payload.event) {
      case 'signIn':
      case 'cognitoHostedUI':
         console.log('signing in user');
         handleSignInEvent(data.payload.data);
         break;
      case 'signOut':
         handleSignOut();
         console.log('user signed out');
         break;
      /*
      case 'signUp':
         console.log('user signed up');
         break;
      case 'signIn_failure':
      case 'cognitoHostedUI_failure':
         console.log('user sign in failed');
         break;
      case 'configured':
         console.log('the Auth module is configured');
      */
   }
   return data;
};
```

**pakage.json** dependency snippet
```
    "@aws-amplify/core": "^5.8.6",
    "@aws-amplify/ui-react": "^5.3.2",
    "@aws-amplify/ui-react-storage": "^2.3.2",
    "aws-amplify": "^5.3.13",
    "react": "^18.2.0",
    "react-app-polyfill": "^3.0.0",
    "react-dom": "^18.2.0",
    "react-redux": "^8.0.4",
    "react-router-dom": "^6.4.1",
    "react-scripts": "5.0.1",
    "redux-saga": "^1.2.1",
    "tss-react": "^4.3.2",
    "typescript": "^4.8.4",
```

When I look in my Browser console I never see the 'Processing Auth Event:' line for my custom domain like I do for the amplifyApp.com domain.
What's going on? Is this a bug in Amplify?

Accepted Answer

The main reason for this might be due to the authentication events are not being triggered as expected.

Ensure that your custom domain is configured to allow cross-origin requests, and the CORS settings for the backend services (e.g., APIs) are correctly configured. Cross-origin issues can prevent events from being triggered.

How do I check that?

Make sure that the OAuth redirect URIs in your Amplify app are updated to include your custom domain (`https://myCustomDomain.org/`).

Make sure that you are using the latest versions of the AWS Amplify libraries (`@aws-amplify/core`, `@aws-amplify/ui-react`, etc.). Update your dependencies to the latest versions and check if the issue persists.

In case if you are still observing the same issue, then reach out to the AWS Premium Support for further troubleshooting of the same.

Amplify Hub not firing on `auth` events. when running from Custom Domain

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