How to maintain ssh-agent login session with Windows 10's new OpenSSH and PowerShell

On my Ubuntu machine, I simply use Keychain to maintain a single ssh-agent which stays logged in.

I'd like something similar to that on Windows now that OpenSSH is natively included. I was using Git Bash with the well-known if [ -z "\$SSH_AUTH_SOCK" ] ; then ... script but this resulted in many ssh agents being opened, I knew it was advised against (partly due to this blog post: http://rabexc.org/posts/pitfalls-of-ssh-agents) - which is what made me get Keychain for Ubuntu. Another reason for not using this any more is that I'm moving to PowerShell as my main shell.

But I'm not sure how to achieve the same kind of thing on Windows specifically with PowerShell and with Win32-OpenSSH.

Thanks!

After that, you need to ssh-add C:\path\to\your\ssh\key\id_rsa only once. After that, everytime the ssh-agent is started, the key will be there. You can check with ssh-add -l.
EDIT: To have SSH agent to automatically start with Windows, you can run Set-Service ssh-agent -StartupType Automatic on a super-user powershell prompt.