Create SSH key
It's best having separate keys on different workstations (e.g., home, office, etc.).
Generate a public key:
ssh-keygen -t rsa -f ~/.ssh/heroku_rsa -C"$(whoami)@$(hostname)"`
We discourage using multiple accounts to deploy code to Heroku, instead add yourself (or ask destination account owner inviting you) as a collaborator to a specific app.
Upload your public key to Heroku:
heroku keys:add ~/.ssh/heroku_rsa.pub
Boring details: https://devcenter.heroku.com/articles/keys