The average person has to remember 27 website passwords. And it kills competition.
Websites are like castles, with large moats around them. You need a password at the gate to get in.
Remembering passwords is a pain. About 30% of all customer queries are "How do I reset my password?"
So websites found a unique solution: outsource the authentication problem to the big castles.
Instead of asking users to enter an email and password, websites now ask users to "connect" them with Google for registration.
Login Service: Hey, could you tell me the name of abc@gmail.com They claim to be your user.
Google: Please show me their signed request.
Login Service: Sure, here you go.
Google: Yes, that's our user. Their name is John Doe.
Login Service: Great. I'll let them in. Could you share their profile picture too?
Gmail: Sorry, but I can't see that in the signed request.
Login Service: Never mind, thanks.
The user is now authenticated, and a session token can be sent for further auth requests.
This process of outsourcing user authentication (technically authorization, since the user authorized you to view their name) is called OAuth.
Third-party sign-in reduces login hesitance, ease of mobile registration, and password reset issues.
It also consolidates data power into a few companies, which know exactly which websites you visited to tailor your ads (Did you register on FirstCry? Let me show you a diaper ad).
You can learn more about OAuth, SSO, and Access Control Lists at InterviewReady.
Cheers!