如何将用户输入值用作AngularJS中其他字段验证的正则表达式的一部分

<div ng-app="myApp" ng-controller="myCtrl">
  <form name="myForm">
    <label for="password">密码：</label>
    <input type="password" id="password" name="password" ng-model="user.password" required>

    <label for="confirmPassword">确认密码：</label>
    <input type="password" id="confirmPassword" name="confirmPassword" ng-model="user.confirmPassword" ng-pattern="/^{{user.password}}[a-zA-Z0-9]*$/" required>

    <div ng-messages="myForm.confirmPassword.$error" role="alert">
      <div ng-message="pattern">密码不符合要求。</div>
    </div>

    <button type="submit" ng-disabled="myForm.$invalid">提交</button>
  </form>
</div>

<script>
  var app = angular.module('myApp', []);
  app.controller('myCtrl', function($scope) {
    $scope.user = {};
  });
</script>