Planning Center has an API that allows you to access most of the information in your account, across multiple apps. Documentation on the available API endpoints is available here.
If your app only needs access to your own data, this is the easiest method for authentication. This is typically how apps that sync data to your ChMS work.
You can get 'Personal Access Tokens' here. You can then use HTTP basic auth to access the API.
curl -u application_id:secret https://api.planningcenteronline.com/services/v2/If you are building an application that will need to log in on behalf of other PCO users, you will use OAuth 2 to authenticate users in your application.
You can register your application and get your Client ID and Secret here.
We have a Ruby example for authenticating with OAuth 2.
All data is returned according to the JSONAPI 1.0 spec.
If you're creating a Ruby application we have the pco_api gem to get you started.
If you have any questions or feature requests, post an issue. We'll take a look and get back to you asap.