cognito custom domain not working

Hello,

Thank you for posting on AWS re:Post!

I see that you have added custom domain to user pool and added A record to Route53 hosted zone but when you use hosted UI you are getting sign in page but after that you are getting Invalid_Request error.

Firstly, as per the information provided, you have added A record to the route 53 hosted zone and created the alias for the custom domain. It appears that you have followed the required steps for adding custom domain to user pool as mentioned in the below AWS reference document.

https://docs.aws.amazon.com/cognito/latest/developerguide/cognito-user-pools-add-custom-domain.html

Secondly, I would like to provide information that generally "invalid_request" would be returned from the user pool's Authorization endpoint. Since you have mentioned that when you use the "View Hosted UI" button it takes you to Cognito sign in page and from there it redirects to https://xxx.herokuapp.com/login?error so I assume that this error might be returned from the authorization end point. Here is the AWS reference document which has listed few reasons for invalid_request error. I would highly recommend checking below reference document.

https://docs.aws.amazon.com/cognito/latest/developerguide/authorization-endpoint.html

Additionally, I would recommend capturing the network trace (HAR) in your browser developer tool that will provide you more insight and possible reason for the error.

Thank you!