How do I implemente "sign in with Twitter" from Javascript now that Anywhere will be deprecated soon?

Question

I did in the past an Implementation with Twitter Anywhere. It worked and it's working very well but I now see that Twitter is sunsetting Anywhere and this fantastic javascript API won't be available anymore. I read the new documentation and I see there is no friendly Javascript API and the only information I found is "do it yourself". The problem is I don't have any idea on how to develop all that functionality and I also can't understand how a brilliant API as Twitter Anywhere will be deprecated while the is no similar new API that really replace it.

Do you know what would be the way to do it now that Anywhere will be deprecated? There are suggestion about using Twitter for website where the login is done automatically when doing a tweet or dooing some actions, but none of them are useful for me as I just use the login to get some information from the user and that's all.

Thanks a lot in advance!