Can someone please explain how secure it is to use the Microsoft account /Nintex Live authentication method to login to an intranet (secure internal portal) for Nintex Mobile app?

My client have some concerns on how secure it is and is questioning that this might potentially open up a security breach if we use Nintex Mobile using a regular microsoft account to authenticate.

Prompt responses are appreciated!

Thanks!

PS: I've also asked my question in response to this blog post.