Authentication

• How do I authenticate with the Calendar data API?
• Why do I receive a "401 Signature Invalid" response when using a signed AuthSub request?
• Why do I receive a "403 Forbidden" error saying the feed I'm trying to update is read-only?
• Why do I receive an "Error=BadAuthentication" response when authenticating via ClientLogin?
• How do I access calendars hosted by Google Apps?
• I'm using an AuthSub token and am getting the error "401 Token revoked" when trying to retrieve a calendar feed. Why?