postship login: sign in from the browser

A code shown in the terminal, “Authorize this device” on postship.fr, and the key lands in ~/.config/postship without ever passing before your eyes. Every device shows up in Account → API and expires after 90 days without use. Along with it: status, open, logout, completion for bash, zsh, fish and PowerShell, complete help per command (postship help, postship docs) and a documentation page for each.