Identity: One ID as Proxy for another ID
I should be able to give another account authorization to act on my account's behalf. Messaging, calling, contact management, payments, everything.
Options for full disclosure ("George skyping for Mary"), partial ("an authorized delegate skyping for May"), and no disclosure.
A lawyer should be able to log in as herself and act on behalf of a client's account.
A parent for a minor child.
An adult child for a parent with dementia.
One employee (signed in as themself) for a corporate account.
A friend for a friend on vacation.
A bot for a user.