The blog is from a hacker who hit on Microsoft and Google for several years. This post is about Google, GSuite, a Microsoft 365 similar product.
In GSuite, there are Super Admins. These users can create groups, manage users, change passwords of users and manage everything else. The author thought "Could I add myself to a GSuite organization and make yourself a super admin?"
The author was looking on domains.google.com. This is a registrar hosted and run by Google. On the registrar, there is a feature that lets a user create a GSuite subscription and manage it from there.
A lot of vulnerabilities in large organizations come when mixing and matching services together. Why does Google Domains have the ability to manage a subscription and add users? I have no idea, but it is there!
If the functionality is existent in this area of the code, it needs to be just as secure as the main location. The author found a trivial IDOR vulnerability on the Google Domains functionality for adding super admins. By setting the ID and name to be another organization, you could create a Super Admin in the other users account.
The outcome of this was the ability to become a Super Admin in any GSuite organization. This is the prized jewel of Google hacking! Finding bugs in large organizations often comes from findings more lax places that implement the original functionality improper.