Why do some services ask for an email first, and then a password, while others ask for both at once?

Question

User identification

Is there any difference under the hood?

Answer 1

It all started with the fact that in addition to the standard login form to the site, login buttons through social networks also began to appear. For example, you registered on the target site using your twitter account. Then you didn't use the target site for some time, then came back and... You definitely remember that you already have an account on this site, but you don't remember which login method you used. There are dozens of different buttons in front of you. Which one should you press? I think the story is familiar to many.
So at some point there was studythe essence of which is to change the login form in such a way that now it is enough for the user to specify only the email address, and then the system itself will determine through which provider the user was registered on the site with this email address and, depending on this, it can either display the password for input, redirect to the provider's site to confirm the login, or immediately authenticate the user on the target site if the user is already logged in and has the necessary permissions for the target site on the provider's site (for example, on twitter.com).
Thus, this is nothing more than an improvement in user experience. But like everything in the world, it has certain disadvantages. For example, now you can find out if a certain user is registered on a certain site knowing only his email address or phone number. That is, privacy suffers.
An implementation example can be seen on the site yandex.ru .

Answer 2

It all depends on the implementation of the backend on these sites

Answer 3

An email with a password is always longer than just an email or just a password. Longer is better, more reliable, safer.