Proposal Details

The current keyring implementation which is returned via keyring.go:37 does only expose the Agent interface for an SSH Agent, but it implements also the ExternalAgent.

// NewKeyring returns an Agent that holds keys in memory.  It is safe
// for concurrent use by multiple goroutines.
func NewKeyring() Agent {
	return &keyring{}
}

The proposal is to implement a constructor returning the ExtendedAgent interface, so one must not reimplement the SignWithFlags functions of the keyring:

// NewExtendedKeyringreturns an ExtededAgent that holds keys in memory.  It is safe
// for concurrent use by multiple goroutines.
func NewExtendedKeyring() ExtendedAgent {
	return &keyring{}
}

This would also keep the interface returned by NewKeyring() stable.