Amazon Cognito User Pools service now supports case insensitivity for user aliases
Amazon Cognito User Pools now enables customers to configure case sensitivity settings for user aliases, including native username, email alias and preferred username alias. With this update, new user pools will be set to case insensitive by default and customers can change the configuration to case sensitive in the console before a user pool is created. Existing user pools will remain as case sensitive. When creating a user pool through Cognito APIs, the user pool will be case sensitive by default. We will change the default setting for the API in the future after a customer notification campaign.
Source:: Amazon AWS