I agree, according to the article, the front end of "email authorization" takes the most time to do. For an MVP a login system really just has to work, and then you can personalize it more as you go. Most of the time for an MVP should be dedicated to the main features of app. (In this case uploading pictures, news feed, etc).
For my app we used Auth0 to quickly get login working before we had to present it. It took about total 5 hours to set up and test. Since then we have built our own login system and made sleek looking create/login screens; which in total took about ~15 hours.
I have played my fair share of MMOs, and the game I spent the most time exploring the world was LOTRO. (lord of the rings online) It has been 5 or so years since I played, so not sure if it is still the same, but back then they had some deeds system where each region had challenges to kill a certain amount of creatures or explore different locations and would reward you with permanent stat boosts. I remember our guild would have nights where we would group up and tackle these challenges together, those are some of my favourite memories in gaming. Sigh, growing up sucks.
For my app we used Auth0 to quickly get login working before we had to present it. It took about total 5 hours to set up and test. Since then we have built our own login system and made sleek looking create/login screens; which in total took about ~15 hours.