Using AngularJS ngModel and Form Validation to $watch two elements and test if they are equal whenever either input changes

What I am trying to do is create a directive which compares two password inputs and triggers invalid if either changes. I have found a few examples and have tried a few and have combined a few in my own attempts. However, I have only been able to toggle the validity with $setValidity when the confirm password field changes. When you change the password field it doesn't trigger the invalidity of the comparison.

Here's my directive:

app.directive("passwordVerify", function() {
    retu {
        require: "ngModel",
        scope: {
            passwordVerify: '=',
        },
        link: function(scope, element, attrs, ctrl) {
            scope.$watch(function() {
                var combined;

                if (scope.passwordVerify || ctrl.$viewValue) {
                    combined = scope.passwordVerify + '_' + scope.$view; 
                }                    
                retu combined;
            }, function(value) {
                if (value) {
                    ctrl.$parsers.unshift(function(viewValue) {
                        var origin = scope.passwordVerify;
                        if (origin !== viewValue) {
                            ctrl.$setValidity("pwd", false);
                            retu undefined;
                        } else {
                            ctrl.$setValidity("pwd", true);
                            retu viewValue;
                        }
                    });
                }
            });
        }
    };
});

Here's the directive in action:

<input id="user_password" type="password" name='user_password' placeholder="password" value='' required ng-model="user.user_password">
<p class="help-text">Required</p>
<div class="help-block" ng-messages="add_user_form.user_password.$error" ng-show="add_user_form.user_password.$touched">
<div ng-messages-include="/app/views/messages.html" ></div>

<input id="confirm_password" ng-model="user.confirm_password" name="confirm_password" type="password" placeholder="confirm password" name="user_confirm_password" required password-verify="user.user_password">
<p class="help-text">Enter matching password</p>
<div class="help-block" ng-messages="add_user_form.confirm_password.$error" ng-show="add_user_form.confirm_password.$touched">
<div ng-messages-include="/app/views/messages.html" ></div>

With this code I can verify that the passwords match when I change the value of the confirm password field, however when you change the value of the password field it doesn't revalidate the input. I'm pretty sure there is a successful way to add $watch to two elements or to use $watchgroup to do this. I just can't figure it out. I know there are a lot of questions on this topic but all I've tried have only gotten me to this point.

I'm using Angular 1.5.7 btw...