Revert ssh-agent behavior pre macOS Sierra

Recently, after updating my workstation to macOS Sierra, I discovered that Apple changed the default behavior of ssh-agent. It no longer auto-loads all the keys stored in Keychain that were added with ssh-add -K. I was able to revert to the pre macOS behavior of ssh-agent by creating a file ~/.ssh/config with the following contents:

Host *
  UseKeychain yes
  AddKeysToAgent yes
  IdentityFile ~/.ssh/id_rsa

Optionally replace ~/.ssh/id_rsa with the path to your key. To add additional keys, add a new line for each key with: IdentityFile /path/to/your_key.