Intercept HTTP Request that needs authorization Header with AngularJS ngResource - api

Question

Hello I'm doing a REST API client with AngularJS using ngResource plugin and my implementation of HMAC authentication.
I wrote an HttpIntercept Service that intercepts the http requests and calculate and attach the Authorization Header with HMAC sign. But with this implementation it calculates and attaches the sign to all requests, that's bad.
.factory('authInterceptor', function($q) {
return {
request: function(request) {
#sign calculation...
request.headers['Authorization'] = sign;
}
return request || $q.when(request);
}
};
})
.controller('HomeCtrl', function ($scope,$resource) {
var Articles = $resource('/api/articles');
$scope.articles = Articles.query();
})
Do you have a suggestion to intercept only requests that needs authentication or all requests that came from ngResource plugin?
I thought to three workrounds:
1. an array list of the private requests
2. different subdomain for public and private APIs
3. attach supply http Header to the requests that need authentication

Answer 1

See $http and overriding transformations and also $resource
Each $resource action takes an $http.config like object which has transformRequest:
var Articles = $resource(
'/api/articles',
{
},
{
'query': {
method: 'GET',
isArray: true,
transformRequest: function (config) {
config.headers['Authentication']: 'sign';
return config;
}
}
});