The typical netizen appreciates being able to log in on various platforms, it's typically the first thing you have to do on a platform so it's understandable that users will find this a very important feature so much so that one might think it's quite a feat (sometimes it is). But what if I tell you that most of the code that goes into creating the core operation of the login and authentication page isn't exactly written by developers anymore? What if I tell you that by clicking on a checkbox, all the code for login and authentication is generated.
I once wrote on scaffolding which explains in some detail how developers are able to speed up development by making use of autogenerated template code in the process of building software solutions. Scaffolding, however, is one of the finer features that is possible based on frameworks. Programming languages are organized and developed into high-level programming constructs that we call frameworks and these frameworks have common use-cases which is what is being scaffolded.
A RELATABLE EXPLANATION
The advantage of frameworks in user login and authentication is obvious in the sense that it speeds up production. This isn't to say that scaffolded login pages are the best way to build login pages, under average circumstances, it should suffice and it's convenient. As with all things in software engineering, it depends on the situation. In average cases where the software solution is assessed to be one that doesn't require enterprise-level architecture, the scaffolding of login and authentication will suffice.
THE MECHANICS OF USER LOGIN AND SIGNUP VIA SOCIAL MEDIA
If you're wondering what this scaffolded login and authentication page looks like I'll describe them. They typically have the "login with Google/Facebook/Microsoft/Twitter" feature in them. Developers who enable you to be able to use those features must be registered. As developers, we register our profession and intention on the developer pages of these social media giants who then give us some unique codes that when inputted in the backend, enables users to be able to register and log into new/existing platforms at the click of a button.
The process of registering as a developer is somewhat simple and in some cases is automatic, however, there are serious consequences to it. Developers will be held accountable for whatever it is they build as it can be tied to them through the login and authentication code. If you're new on a platform and you choose to signup using your social media account, the platform you're on checks if you're a registered user, when it confirms that you're not, it initiates a digital handshake with the social media platform you chose.
The social media platform will then provide some of your details (eg name, email, etc) after getting your permission, to the new platform. The new platform will use these details to create an account for you automatically and you get signed in. This is how you signup via the social media feature 😉. Login involves less back and forth once you do the typical authorization.
FINALLY
By now, it's easy to tell that manually writing the code that does all these will be somewhat tedious. Scaffolding this part can save hours if not days of the developer's time. It is worth acknowledging that not all frameworks give this much convenience, much of what is written here is based on my experience with Microsoft ASP.Net. Also worthy of note is that some enterprise solutions require more bespoke login and authentication processes.