AngularJS: How to send auth token with $resource requests?

Question

I want to send an auth token when requesting a resource from my API.

I did implement a service using $resource:

factory('Todo', ['$resource', function($resource) {
 return $resource('http://localhost:port/todos.json', {port:":3001"} , {
   query: {method: 'GET', isArray: true}
 });
}])

And I have a service that stores the auth token:

factory('TokenHandler', function() {
  var tokenHandler = {};
  var token = "none";

  tokenHandler.set = function( newToken ) {
    token = newToken;
  };
  tokenHandler.get = function() {
    return token;
  };

  return tokenHandler;
});

I would like to send the token from tokenHandler.get with every request send via the Todo service. I was able to send it by putting it into the call of a specific action. For example this works:

Todo.query( {access_token : tokenHandler.get()} );

But I would prefer to define the access_token as a parameter in the Todo service, as it has to be sent with every call. And to improve DRY. But everything in the factory is executed only once, so the access_token would have to be available before defining the factory and it cant change afterwards.

Is there a way to put a dynamically updated request parameter in the service?

Answer 1

Thanks to Andy Joslin. I picked his idea of wrapping the resource actions. The service for the resource looks like this now:

.factory('Todo', ['$resource', 'TokenHandler', function($resource, tokenHandler) {
  var resource = $resource('http://localhost:port/todos/:id', {
    port:":3001",
    id:'@id'
    }, {
      update: {method: 'PUT'}
    });

  resource = tokenHandler.wrapActions( resource, ["query", "update"] );

  return resource;
}])

As you can see the resource is defined the usual way in the first place. In my example this includes a custom action called update. Afterwards the resource is overwritten by the return of the tokenHandler.wrapAction() method which takes the resource and an array of actions as parameters.

As you would expect the latter method actually wraps the actions to include the auth token in every request and returns a modified resource. So let's have a look at the code for that:

.factory('TokenHandler', function() {
  var tokenHandler = {};
  var token = "none";

  tokenHandler.set = function( newToken ) {
    token = newToken;
  };

  tokenHandler.get = function() {
    return token;
  };

  // wrap given actions of a resource to send auth token with every
  // request
  tokenHandler.wrapActions = function( resource, actions ) {
    // copy original resource
    var wrappedResource = resource;
    for (var i=0; i < actions.length; i++) {
      tokenWrapper( wrappedResource, actions[i] );
    };
    // return modified copy of resource
    return wrappedResource;
  };

  // wraps resource action to send request with auth token
  var tokenWrapper = function( resource, action ) {
    // copy original action
    resource['_' + action]  = resource[action];
    // create new action wrapping the original and sending token
    resource[action] = function( data, success, error){
      return resource['_' + action](
        angular.extend({}, data || {}, {access_token: tokenHandler.get()}),
        success,
        error
      );
    };
  };

  return tokenHandler;
});

As you can see the wrapActions() method creates a copy of the resource from it's parameters and loops through the actions array to call another function tokenWrapper() for every action. In the end it returns the modified copy of the resource.

The tokenWrappermethod first of all creates a copy of preexisting resource action. This copy has a trailing underscore. So query()becomes _query(). Afterwards a new method overwrites the original query() method. This new method wraps _query(), as suggested by Andy Joslin, to provide the auth token with every request send through that action.

The good thing with this approach is, that we still can use the predefined actions which come with every angularjs resource (get, query, save, etc.), without having to redefine them. And in the rest of the code (within controllers for example) we can use the default action name.