In this recipe, we created an Amazon Cognito user pool retaining most of the defaults, but changing the user attributes' configuration. We created a few alias attributes. 

By default, we can sign in using a username. We can add additional attributes as alias attributes and then use these to sign in. Allowed values for alias attributes are email, phone, or preferred username. We can also use one or both of email or phone number as the username and then use these to sign in instead of username, as shown in the following screenshot:

We can only specify either the alias attributes or username attributes, but not both. Within the console, this is enforced by using radio buttons. When we are using APIs (using the AWS CLI or AWS SDK), we need to make sure we specify only one of them.