to provide access from one account to the data of another
<p>I'm going to develop a multiuser system, where people can register an account, log in, store and manage the data of the account. For example, email address idetifiers a user.
Could you tell, please, how to provide the user of one account  access to the data of another account. For example, by providing a link in the account that gives access to another account.
It looks like Google Analytics uses a mechanism similar to this one to give access of one user access to the account of another user.
Thanky you very much, Oleg.</p>
