Create a web service API

We manage a database containing customers' financial data. We want to build an API which will allow third-party developers to access the information in the database on behalf of individual customers. 3rd party developers will be issued with a token and a token secret. Customer registration is handled using the OAuth protocol. Once a customer is registered, the developers can then extract the customer's information held in our database for use in their own applications. We need a skilled PHP developer to design, implement and fully test this API. This is an urgent project, and we are looking to award it quickly. In your response, please explain your understanding of the OAuth protocol.