Moritz Tolxdorff shared this feature on his Google+ profile
It is not clear when this feature was rolled out but it is a very significant update.
Google+ Page owners can now set a unique username and password for their pages.
This would allow them to directly login to the page skipping their own personal account in the process.
With this, they also get access to third party apps on Google+ services like Hangouts. This comes very handy for Page owners as they can now link YouTube accounts to specific Google+ Page for Hangouts on Air.
Google spoke about this feature:
By setting up a username and password for your Google+ page, you’re able to take advantage of numerous third party tools that link to your Google account. You’ll also be able to sign in directly to your page instead of going through another account that owns or manages the page. You’ll also be able to use other Google services when logged in as your page, such as YouTube and Gmail.