Symantec has developed an Open Source system for short-term SSH and SSL certificate management with 2FA (VIP and U2F). We encourage people to adopt this to improve their security.
Code: https://github.com/Symantec/keymaster
Design document: https://docs.google.com/document/d/1AW3UROCJqTc3R4MLJXxmPUNS...
Disclaimer: *I work for ManageEngine.