How does Sunrise for iOS use iCloud credentials to access our calendar?

Question

Sunrise on iOS is calendar that, with version 2, added support for iCloud calendars. From this page, the team at Sunrise say this:

When you type in your i

Answer 1

They moved the portion of the code that did the authentication to the client. So if you know how to authenticate with iCloud on your server, you know how to do it on the client. On the client, an authorization request is made and if that succeeds, the authorization token is then sent to the server. This token is valid for a certain amount of time (or indefinitely). The server uses the token when sending requests to Apple.

If I recall correctly, Apple uses Kerberos for iCloud. So after authentication, the server creates a ticket, which then any client can use for requests. The ticket is what is sent to the server.