After registering your app (see Developer and Application Registration) with the API provider and obtaining an OAuth client ID and client secret, it’s time to start writing code! Let’s go through each step of the flow and show how the protocol works. We’ll use PHP as the example programming language and the Google Tasks API along with Google’s OAuth 2.0 authorization server.

Although we’ll write the PHP code using the raw OAuth protocol, many API providers distribute client libraries for accessing their services. These libraries abstract away some of the details of implementing OAuth 2.0 and make it easier for developers. You can find information on Google’s PHP library, which works with Google Tasks, Google+, and many other Google APIs, at code.google.com.