[lib] update currentAsOf for SIWE auth

Summary:
Updating this to have correct type.

This partially caused ENG-5883.
We were returning 0 as the default value for currentAsOf in here: link.
This later caused a condition from D9965 truthy right after login.

Test Plan:

1. Log currentAsOf
2. Log in using SIWE
3. Make sure it has correct type and value (previously it was number, not object).

Reviewers: inka, tomek, michal, ashoat

Reviewed By: ashoat

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D10058