Build a PHP-based Coinbase API

I'm looking to develop a PHP application that integrates with the Coinbase API. The app needs to have the following functionalities:

- User Authentication: Implement OAuth for secure logins.
- User Info Retrieval: Fetch and display user information.
- Cryptocurrency Overview: Enable users to view all available coins.
- Transaction Capability: Allow users to withdraw coins.
- Database Utilization: Use SQL to store user info, transaction logs, and coin data.

The application should be capable of fetching real-time data for coin prices.

Ideal skills and experience for the job:
- Extensive knowledge of PHP and SQL.
- Proven experience with the Coinbase API.
- Familiarity with implementing OAuth for user authentication.
- Ability to develop applications that fetch real-time data.
- Experience in setting up databases to store various types of information.