Tag Archives: json

Web API security basics

When I proposed the lead developer of an open source web application to enable JSONP for the API, the developer replied:

The whole thing sounds easy enough to implement, but I have some doubts that it will open the project to XSS attack of some sort. Don’t really know why, though. :-)

We mailed a bit more about the risks of cross site scripting and then he wrote the following:

Sadly we can have malicious JS problems since cleaning up of incoming data is optional.

For an unrelated project I asked about authentication for a write-operation in the API and the reply was:

Authentication is not in the API yet. Currently you must include a session cookie along with API requests to perform a write, but the cookie itself is the one you get from logging in [in the web front end] as you would normally.

Which sounds a lot like “we support cross site request forgery out of the box” …

As with normal web applications, web API-security is an important (but complex) issue, which is not always easy to grasp. Based on a basic understanding of things, the following guidelines can go a long way into securing things both on the API-side and the client:

  1. Know who you’re dealing with; disable API-access for your users by default (allowing them to opt-in), provide bullet-proof authentication and session management in the API and throw in a synchronizer token to prevent cross site request forgery
  2. Never trust input from users or external systems; decide what to trust and filter out everything that’s not in that white-list (SQL-code, server-side code, javascript, and even html and css)

If you apply these basic principles to JSONP (make sure to filter the callback-parameter and set the correct content-type in your response) you’ll have a whole lot less to worry about!

More info:

No more jsonp for Google geocoding webservice?

I needed to do some reverse geocoding in a javascript webapp. The Google Maps API worked flawlessly, but it seemed overkill to load all that javascript just to do one lousy reverse geocoding lookup (esp. on a mobile device, my target platform).  I searched some more and found the Google geocoding webservice, which is invoked with a simple HTTP GET request and returns the response in JSON. Version 2 of this service works great, as you can specify a callback-function to do jsonp (a simple method to allow for cross domain ajax requests),

This example request for v2, http://maps.google.com/maps/geo?q=51,4&sensor=false&output=json&callback=parseme, results in a response containing a call to your own “parseme”-function, with the json-object as the payload;

parseme && parseme( {
"name": "51,4",
"Status": {
"code": 200,
"request": "geocode"
},
"Placemark": [ {
"id": "p1",
"address": "Brukkelen 191, 9200 Dendermonde, Belgium",
...
]})

But a month ago Google announced a new version of their geocoding webservice and the documentation for V2 mentioned that it was deprecated in favor of the Geocoding V3 Web Service. so I switched to the new API, only to discover that callbacks aren’t supported any more.

An example request for v3 http://maps.google.com/maps/api/geocode/json?latlng=51,4&sensor=false&callback=parseme results in nothing but the javascript-object:

{
"status": "OK",
"results": [ {
"types": [ "street_address" ],
"formatted_address": "Brukkelen 191, 9200 Dendermonde, Belgium",
...
]})

And that, my dear fellow travellers, sucks big time. JSON without the P means we’re back to useless proxy-scripts on our servers. So until Google lets Jason pee (sorry folks, I just had to write this) in the V3 geocoding webservice, I’ll continue using the deprecated V2 with sweet -but undocumented- callback!

Switching from Google Reader to Tiny Tiny RSS

Given the concerns about the enormous amount of data Google continuously collects about its users and because of the fact that their CEO seems to have a poor understanding of privacy (Schmidt stated “If you have something that you don’t want anyone to know, maybe you shouldn’t be doing it in the first place”) and despite Google’s Jonathan Rosenberg recent manifesto on openness I decided to move some of my online activities away from the all-seeing eye of  Google. After switching to scroogle.org for normal search, I now found an alternative for Google Reader as well in Tiny Tiny RSS.

Tiny Tiny RSS (or “tt-rss” for short) is an open source web application written in PHP with a PostgreSQL or MySQL database. The webapp is AJAX-based, multi-user and is offline-enabled using Google Gears (you can check out a demo here). There’s also a mobile version, a (deprecated) XML-RPC API and a brand new experimental JSON-API, which I’m playing around with, using XUI to write a minimal mobile version of my own.

For those who are not able to install and configure tt-rss or who don’t want to burden their server with it, developer Andrew Dolgov put up a hosted version (thanks Andrew!) where currently 8 more users can register.

After having switched about a week ago, I find I barely miss Google Reader, although tt-rss still feels a little rough around the edges at times. The only real limitation is that shared items (‘published’ in tt-rss) off course aren’t automagically shared with your Google friends. I now automatically import my tt-rss published articles and manually share those every few days in Reader. Because I wouldn’t want to disappoint my Google friends, now would I?