rm "username" from being parsed in amplify_outputs.json auth.username_attributes

[josefaidt]

Description of changes

modifies parseAmplifyOutputs to look for an empty array in auth.username_attributes instead of ["username"] to determine whether logging in with username is enabled

this is related to a similar change in the backend repo to remove username from the list of username_attributes in the outputs schema aws-amplify/amplify-backend#1636

valid username_attributes properties include email and phone_number https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_cognito.CfnUserPool.html#usernameattributes

these values come from the L1 CfnUserPool property, therefore will not include username but the absence of attributes that can be used in place of the username
https://github.com/aws-amplify/amplify-backend/blob/main/packages/auth-construct/src/construct.ts?rgh-link-date=2024-06-19T22%3A39%3A40Z#L952

Issue #, if available

Description of how you validated changes

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[israx]

if the backend is changing, then this fix makes sense. But I wonder if we should also support previous versions to avoid any breaking change.

Suggested change

	username: username_attributes.length === 0,
	username: username_attributes.length === 0 || username_attributes.includes('username') ,

[josefaidt]

this was written with the outputs schema that had a reference to "username" for this value, however "username" would not be emitted from the construct. for this field, the absence of username attributes indicates "username"