Investigate SSH certificates

[mutantmonkey]

We need to find some way to handle SSH authentication if we move all authentication to Google. SSH certificates have been suggested as a good way to do this, so we should investigate if that will work for us. If so, we should create another issue to actually roll out their use.

[mutantmonkey]

Some links to check out:

• https://github.com/cloudtools/ssh-cert-authority
• https://github.com/Netflix/bless
• https://github.com/nsheridan/cashier
• https://github.com/uber/pam-ussh

[mutantmonkey]

I found another option (Smallst*p Certificates) that might work well, but after they spammed me I strongly suggest removing it from consideration.