I have a web app that has a REST API interface: http://api.example.com/core that uses API Keys and domain specific keys (key has to be used on the specified domain).

I then will have several client sites with ajax forms where we will require users to sign in before being able to submit the form. This form will add data to a table, and submit an email to several recipients along with checking credentials.

This form will use an ajax submit to our REST API.

All Communication to/from the API is over SSL

Ideal Flow: Visitor Fills Form Out -> Enters User/pass -> Submits Form -> ajax request to REST API -> API Verifies credentials -> does CRUD -> sends emails -> returns 200/403 -> perform DOM manipulation based on return code in ajax call

Are there any libraries in PHP that currently do something to this similarly? Would OAuth be a good use for this scenario?

Languages used are: js/html/css/php/MySQL