PHP External API

I'm looking to build an API that users can call, so that they can integrate our app with their own processes. Most of the database and php models have already b开发者_Go百科een created.

I'm looking for a tutorial with examples on the best way to accomplish this. Must include all the security considerations as well.

I'd like to use an established framework to assist with this - so far CodeIgniter has caught my eye as being the easiest to get to grips with. I'm open to suggestions though.

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Here is a nice tutorial that explains you the basics to do it yourself: http://www.gen-x-design.com/archives/create-a-rest-api-with-php/

Or if you're more comfortable with a framework Recess is a nice one to consider: http://www.recessframework.org/