Based on a Twitter conversation with @marcysutton: https://twitter.com/dpogue/status/569999089967849472

If I have <input type="text" ng-model="username" name="username" required> and I'm using ngAria then it should have the aria-required attribute added to it.

This currently only happens when the field doesn't have content (i.e., when username.$error.required is true):
https://github.com/angular/angular.js/blob/master/src/ngAria/aria.js#L292-L298