How to use different ssh deploy keys for multiple private github repositories with Go Modules

Let's assume you are using Go Modules and have a go.mod file that contains multiple private repos each with a different ssh key. How can you get go mod download to do the right thing -- i.e. use ssh key A with private repo A and ssh key B with private repo B?

Ok, here we go!

Let's assume you have some github.com user with multiple private repos:

https://github.com/someuser/private-repo-1