Automatically load keys into the ssh-agent and store passphrases in the keychain: (see step 2)
If you're using macOS Sierra 10.12.2 or later, you will need to modify your ~/.ssh/config file to automatically load keys into the ssh-agent and store passphrases in your keychain.
First, check to see if your ~/.ssh/config file exists in the default location.
$ open ~/.ssh/config
> The file /Users/YOU/.ssh/config does not exist.
If the file doesn't exist, create the file.
$ touch ~/.ssh/config
Open your ~/.ssh/config file, then modify the file to contain the following lines. If your SSH key file has a different name or path than the example code, modify the filename or path to match your current setup.
Host *.github.com
AddKeysToAgent yes
UseKeychain yes
IdentityFile ~/.ssh/id_ed25519