Several users have noticed that iCloud.com is once again employing two-factor authentication for users who have activated the security measure. The two-step process first popped up on the iCloud web portal back in June, but the feature was quickly pulled for unknown reasons.
For those unfamiliar with Apple's implementation of two-factor authentication, it requires users to verify their identity via text message or Find My iPhone push notification. It provides an extra layer of security in the event a user's device or Apple ID info becomes compromised.