Actually, you can’t do this.
These Internet services have been built with the same security goals
that iOS promotes throughout the platform. These goals include secure
handling of data, whether at rest on the device or in transit over
wireless networks; protection of users’ personal information; and
threat protection against malicious or unauthorized access to
information and services. Each service uses its own powerful security
architecture without compromising the overall ease of use of iOS.
From iOS Security (PDF), page 58.
You can obtain data which is “binded” with your app only, and if user allowed access.
solved How can I get all account info saved in iPhone?