What about a conf file for this? Like, pass a flag pointing to a conf file at a file location, or accepting https:// locations or something.

At that conf file, I'm thinking go-config so it supports TOML, YAML, and JSON out of the box. Maybe read from that conf file just a map[string]string[] of websites to usernames? That way someone's SSH keys could be pulled from github, or gitlab, or also their corporate gitlab install?