Issue
Some remote servers are not set up with a browser. Sometimes users need to access Heroku using the Heroku CLI.
Resolution
You can use the flag -i with the CLI login command which will prompt you to enter your credentials on the CLI itself without using a browser.
heroku login -i
This command is documented here: https://devcenter.heroku.com/articles/heroku-cli#getting-started
Note:- You can't use the -i option if you have multi-factor authentication enabled due to a technical dependency on web browsers for verification.