[lib] add method to parse one-time keys

Summary:
Add method which parses keys to store entire object.
Some context in ENG-6099.

Test Plan: Make sure keys output is correct, and it's possible to create session (later in the stack).

Reviewers: marcin, varun, michal

Reviewed By: marcin, varun

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10368