[Feature Request] support osx keyring auth w/o using a macos dialog box

[jinyius]

an offshoot of https://github.com/99designs/aws-vault/issues/535

it would be nice if the --prompt=terminal flag would also force any keyring auth to use cli prompts instead of the native keyring dialog box that pops up (without focus i might add, which means i have to move my hands away from the keyboard). this is especially beneficial if you're connected remotely to your machine via ssh.

there is a way to do keyring unlocking using the security command:

security unlock $HOME/Library/Keychains/aws-vault.keychain-db

but unfortunately, this command isn't smart enough to know if the keyring is already unlocked so it always requests for your password even if it's unlocked. also, there's no other security subcommand or other mechanism within macos to figure out if a keyring is already unlocked through the command line afaict.

thanks!