Prevent $http service execution using Interceptor - angularjs

Question

I am building an authentication solution with Angular. I am using Interceptors to validate Request and if there is not valid token prevent from further processing and redirect. Here is my simplified Interceptor:
prism.service('APIInterceptor', function($rootScope) {
var service = this;
service.request = function(config) {
.....
return config;
};
})
Just for the sake of POC that I am working on what would the correct way of stopping this request from any further processing be?
Thanks

Answer 1

From the Angular Docs on Interceptors for the request method:
request: interceptors get called with a http config object. The function is free to modify the config object or create a new one. The function needs to return the config object directly, or a promise containing the config or a new config object.
The rest of the documentation can be found here. From this you can see that the method can also return a promise (which is actually pretty awesome) so you could always reject it.
Try something like this:
prism.service('APIInterceptor', function($q, $rootScope) {
this.request = function(config) {
if( /*config is not valid*/ ) {
return $q.reject({message: 'ERROR, ERROR... INTRUDER ALERT!', status: 401, config: config});
} else {
return config;
}
};
});
And see how it might be handled (I have no idea what your application will do). Let me know if it works out for you!
EDIT: My answer has been accepted, but is incomplete and it will haunt me forever if I don't complete it. So, after writing some test code of my own I've realized that you can do 1 of 2 things in this situation. The first is to handle the unauthorized request in the interceptor:
...
this.request = function(config) {
if(/* config is not authorized */) {
// Do something here like redirect/issue another request... whatever
return $q.reject({/*whatever the hell you want*/});
} else ...
};
...
This obviously works best if you want to handle all unauthorized requests the same. If you don't, however, the second option is to defer to the service that issued the request. For example, if you're using $http you can do this:
$http.get('/words/words/words/').then(function(){
// This is where you handle a successful request.
}, function(error) {
// Handle your error here. Please take note that this error message is
// whatever you sent back in the `reject` previously
});
Hopefully that clears a few things up.