[iso-core] cleanup auth helpers connect fn
[iso-core] cleanup auth helpers connect fn

Summary:
No logical change. Just code re-org and comments to make it much clearer
what's going on

Test Plan: manual

Reviewers: spang, halla, juan

Reviewed By: juan

Differential Revision: https://phab.nylas.com/D4460

nylas-mail-lives/nylas-mail,simonft/nylas-mail,nylas/nylas-mail,simonft/nylas-mail,simonft/nylas-mail,nirmit/nylas-mail,nylas/nylas-mail,nylas/nylas-mail,nirmit/nylas-mail,simonft/nylas-mail,nylas-mail-lives/nylas-mail,nirmit/nylas-mail,nylas-mail-lives/nylas-mail,nylas-mail-lives/nylas-mail,nirmit/nylas-mail,nylas/nylas-mail,nylas/nylas-mail,nirmit/nylas-mail,simonft/nylas-mail,nylas-mail-lives/nylas-mail