Add support for SSH Agent

builtin/provisioners/file/resource_provisioner.go

@@ -60,6 +60,7 @@ func (p *ResourceProvisioner) copyFiles(conf *helper.SSHConfig, src, dst string)
 	if err != nil {
 		return err
 	}
+	defer config.CleanupConfig()
 
 	// Wait and retry until we establish the SSH connection
 	var comm *helper.SSHCommunicator

builtin/provisioners/remote-exec/resource_provisioner.go

@@ -172,16 +172,20 @@ func (p *ResourceProvisioner) runScripts(
 	if err != nil {
 		return err
 	}
+	defer config.CleanupConfig()
 
 	o.Output(fmt.Sprintf(
 		"Connecting to remote host via SSH...\n"+
 			"  Host: %s\n"+
 			"  User: %s\n"+
 			"  Password: %v\n"+
-			"  Private key: %v",
+			"  Private key: %v"+
+			"  SSH Agent: %v",
 		conf.Host, conf.User,
 		conf.Password != "",
-		conf.KeyFile != ""))
+		conf.KeyFile != "",
+		conf.Agent,
+	))
 
 	// Wait and retry until we establish the SSH connection
 	var comm *helper.SSHCommunicator

helper/ssh/communicator.go

@@ -97,6 +97,10 @@ type Config struct {
 
 	// NoPty, if true, will not request a pty from the remote end.
 	NoPty bool
+
+	// SSHAgentConn is a pointer to the UNIX connection for talking with the
+	// ssh-agent.
+	SSHAgentConn net.Conn
 }
 
 // New creates a new packer.Communicator implementation over SSH. This takes

helper/ssh/provisioner.go

@@ -5,12 +5,15 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"net"
+	"os"
 	"time"
 
-	"golang.org/x/crypto/ssh"
 	"github.com/hashicorp/terraform/terraform"
 	"github.com/mitchellh/go-homedir"
 	"github.com/mitchellh/mapstructure"
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/agent"
 )
 
 const (
@@ -37,6 +40,7 @@ type SSHConfig struct {
 	KeyFile    string `mapstructure:"key_file"`
 	Host       string
 	Port       int
+	Agent      bool
 	Timeout    string
 	ScriptPath string        `mapstructure:"script_path"`
 	TimeoutVal time.Duration `mapstructure:"-"`
@@ -99,9 +103,32 @@ func safeDuration(dur string, defaultDur time.Duration) time.Duration {
 // PrepareConfig is used to turn the *SSHConfig provided into a
 // usable *Config for client initialization.
 func PrepareConfig(conf *SSHConfig) (*Config, error) {
+	var conn net.Conn
+	var err error
+
 	sshConf := &ssh.ClientConfig{
 		User: conf.User,
 	}
+	if conf.Agent {
+		sshAuthSock := os.Getenv("SSH_AUTH_SOCK")
+
+		if sshAuthSock == "" {
+			return nil, fmt.Errorf("SSH Requested but SSH_AUTH_SOCK not-specified")
+		}
+
+		conn, err = net.Dial("unix", sshAuthSock)
+		if err != nil {
+			return nil, fmt.Errorf("Error connecting to SSH_AUTH_SOCK: %v", err)
+		}
+		// I need to close this but, later after all connections have been made
+		// defer conn.Close()
+		signers, err := agent.NewClient(conn).Signers()
+		if err != nil {
+			return nil, fmt.Errorf("Error getting keys from ssh agent: %v", err)
+		}
+
+		sshConf.Auth = append(sshConf.Auth, ssh.PublicKeys(signers...))
+	}
 	if conf.KeyFile != "" {
 		fullPath, err := homedir.Expand(conf.KeyFile)
 		if err != nil {
@@ -140,8 +167,17 @@ func PrepareConfig(conf *SSHConfig) (*Config, error) {
 	}
 	host := fmt.Sprintf("%s:%d", conf.Host, conf.Port)
 	config := &Config{
-		SSHConfig:  sshConf,
-		Connection: ConnectFunc("tcp", host),
+		SSHConfig:    sshConf,
+		Connection:   ConnectFunc("tcp", host),
+		SSHAgentConn: conn,
 	}
 	return config, nil
 }
+
+func (c *Config) CleanupConfig() error {
+	if c.SSHAgentConn != nil {
+		return c.SSHAgentConn.Close()
+	}
+
+	return nil
+}

website/source/docs/provisioners/connection.html.markdown

@@ -46,6 +46,8 @@ The following arguments are supported:
 * `key_file` - The SSH key to use for the connection. This takes preference over the
    password if provided.
 
+* `agent` - Set to true to enable using ssh-agent to authenticate.
+
 * `host` - The address of the resource to connect to. This is provided by the provider.
 
 * `port` - The port to connect to. This defaults to 22.