As you guys requested I have finally updated the old Android Login Registration System tutorial with newer code and API. It has all the previous features except Reset Password via Email. I will add that functionality soon and post as separate tutorial.
Some of the changes in Server when compared to the old one,
-> Use PHP PDO for working with MySQL database which is more secure and prevents SQL injection.
-> Code is cleaned and simplified. The total files is 3 instead of 5.
-> Hash password using default PHP BCRYPT algorithm instead of SHA.
-> JSON input instead of form urlencoded data input.