Access to iCloud calendar for users without saving password

I would like to create a web application that will have access to the Apple Calendar user for a personal project. But I really don't want to store the user's password.

With google it was very easy using OpenAuth.

I know this is possible as SunRise does it - http://techcrunch.com/2014/01/31/sunrise-calendar-stops-sending-icloud-credentials-to-their-servers/

I've searched Apple's documentation and the closest thing I've found is CloudKit. But it looks like it only provides access to your app data in all locations. No mention of iCloud services.

Am I going in the right direction or is there a more direct way to do this? Or the shine of SunRise :)