code: func (c *client) Signers() ([]ssh.Signer, error) {
  	keys, err := c.List()
  	if err != nil {
  		return nil, err
  	}
  
  	var result []ssh.Signer
  	for _, k := range keys {
  		result = append(result, &agentKeyringSigner{c, k})
  	}
  	return result, nil
  }
docs: // Signers provides a callback for client authentication.