builder/scaleway: support ssh agent authentication

builder/scaleway/ssh.go

@@ -2,10 +2,13 @@ package scaleway
 
 import (
 	"fmt"
+	"net"
+	"os"
 
 	packerssh "github.com/hashicorp/packer/communicator/ssh"
 	"github.com/mitchellh/multistep"
 	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/agent"
 )
 
 func commHost(state multistep.StateBag) (string, error) {
@@ -19,12 +22,27 @@ func sshConfig(state multistep.StateBag) (*ssh.ClientConfig, error) {
 
 	var auth []ssh.AuthMethod
 
-	if config.Comm.SSHPassword != "" {
+	if config.Comm.SSHAgentAuth {
+		authSock := os.Getenv("SSH_AUTH_SOCK")
+		if authSock == "" {
+			return nil, fmt.Errorf("SSH_AUTH_SOCK is not set")
+		}
+
+		sshAgent, err := net.Dial("unix", authSock)
+		if err != nil {
+			return nil, fmt.Errorf("Cannot connect to SSH Agent socket %q: %s", authSock, err)
+		}
 		auth = []ssh.AuthMethod{
+			ssh.PublicKeysCallback(agent.NewClient(sshAgent).Signers),
+		}
+	}
+
+	if config.Comm.SSHPassword != "" {
+		auth = append(auth,
 			ssh.Password(config.Comm.SSHPassword),
 			ssh.KeyboardInteractive(
 				packerssh.PasswordKeyboardInteractive(config.Comm.SSHPassword)),
-		}
+		)
 	}
 
 	if config.Comm.SSHPrivateKey != "" {