Displaying error message in Cognito managed login sign-in page

Unfortunately, it is not currently possible to customize or display custom error messages within the Managed Login UI of Amazon Cognito, including displaying the errorMessage parameter from the URL.

The Managed Login UI provides a standardized authentication experience with limited customization options. While it offers features like multi-provider authentication and a ready-to-use interface, it does not allow for the level of customization that would enable displaying custom error messages or modifying the existing error handling behavior.

When errors occur during the authentication process, such as entering an email associated with an unregistered identifier, Amazon Cognito typically redirects users back to the login page with error information in the URL parameters. However, the Managed Login UI does not automatically display these custom error messages within its interface.

This limitation is consistent across various error scenarios in Cognito's Managed Login. For instance, even in cases where an invalid client ID is provided, the system redirects to a generic error page without the ability to customize the displayed message.

If displaying custom error messages or having more control over the error handling process is crucial for your application, you might need to consider alternative approaches. These could include implementing a custom authentication UI or using the Amazon Cognito API directly to handle authentication flows and error messaging in a way that better suits your specific requirements.

It's worth noting that while this limitation exists in the current implementation of Managed Login, Amazon Web Services regularly updates and improves its services. Therefore, it's advisable to keep an eye on AWS documentation and announcements for any future enhancements that might address this need.
Sources
Updating a Cognito Login Error Message | AWS re:Post
User pool managed login - Amazon Cognito
Common Amazon Cognito terms and concepts - Amazon Cognito