at https://core.telegram.org/widgets/login (at least skim it!)
People using Docker see their own paragraph below.
https://github.com/simonneutert/ruby-telegram-login-web-stub-tutorial
have ngrok installed and start a server by $ ngrok http -p 5555
and copy the https url you are given
.env
(copy of .env.example) edit with your credentials/setdomain
run it local using Ruby or with Docker
$ bundle install
.rackup -p 5555
clap your hands and login with telegram!
B-)
$ docker build . -t ruby-telegram-login
$ docker run -it --rm -p5555:5555 ruby-telegram-login
if you messed up a step above, simply build again, then run again, again, again