EDIT by @4ian in 2022: you can now add Leaderboards to your game using built-in leaderboards provided by GDevelop and Liluo.io. Read more here: Leaderboards [GDevelop wiki]
I need to create an online leaderboard with authentication. Once logged in, then every time I open the app it should log in automatically. leaderboards should display the scores in descending order up to 50 players. How to link player id from the authentication to the scores. Any tutorials?
Hello Mr. @Lucifer24. I want to give you some advice. I don’t want to hurt your feelings but, at first, if you are just learning, try making basics. Don’t go on a hit or big project. At first, understand how things work. I think the online leaderboard itself is very (if not) complicated. And descending order up to 50 players is more.
And at last,
Thanks for reading 
you can try with www.crimsongames.io there is some example project for GDevelop 5
You can Set your players to use an email and nickname to login into and add scores as well.
Other option is to use Firebase