AngularJS Storing userID in post operation - angularjs

Question

Edit (to make it more clear) I currently have a post methode where I post a birdname and location to my mongodb. But inside this post methode I also want to add the userID of the person that is logged in and posting the capture.
This way I can link the capture posted by him/her to their account.
Edit 2: The id of the capture is set through mongodb. My intent is to add the userID (of the user that is logged in and doing the post opperation) to be added into it all.
I'm working with AngularJS and Mongodb and as Authentication system I have integrated Auth0.
The code I currently have is posted below:
// Api.js ($resource for where to store the capture):
/* global app */
app.factory('Api', ['$resource', function($resource){
return {
Capture: $resource('/api/captures/:id', {id: '#id'})
}
}])
// CaptureCtrl.js - I can retrieve the user's id as shown below (inside the console.log):
/* global app */
app.controller('captureCtrl',[ '$scope', 'Api', 'auth', function($scope, Api, auth){
$scope.form = {};
$scope.auth = auth;
console.log($scope.auth.profile.user_id);
$scope.addToDatabase = function() {
console.log('button clicked');
Api.Capture.save({}, $scope.form, function(){
$scope.form = {};
})
}
}]);
// Capture.html - I don't want to add a extra input seeing it should be done behind the scene (obviously):
<form class="well" name="addCapture">
<div class="form-group">
<label for="birdname">Birdname</label>
<input type="text" class="form-control" id="birdname" ng-model="form.birdname" required>
</div>
<div class="form-group move-down">
<label for="place">Picture taken in:</label>
<input type="text" class="form-control" id="place" ng-model="form.place" ng-autocomplete required>
</div>
<div class="form-group">
<button type="submit" class="btn margin-left btn-success" ng-click="addToDatabase()" ng-disabled="addCapture.$invalid">Add Customer</button>
</div>
</form>
How would I add this into the code?
I've tried a couple of options but I keep getting errors.