Add ssh agent to enable SSH-CA authentication.

builder/openstack/builder.go

@@ -110,7 +110,9 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 				computeClient,
 				b.config.SSHInterface,
 				b.config.SSHIPVersion),
-			SSHConfig: SSHConfig(b.config.RunConfig.Comm.SSHUsername,
+			SSHConfig: SSHConfig(
+				b.config.RunConfig.Comm.SSHAgentAuth,
+				b.config.RunConfig.Comm.SSHUsername,
 				b.config.RunConfig.Comm.SSHPassword),
 		},
 		&common.StepProvision{},

builder/openstack/ssh.go

@@ -4,6 +4,8 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"net"
+	"os"
 	"time"
 
 	"github.com/gophercloud/gophercloud"
@@ -12,6 +14,7 @@ import (
 	"github.com/mitchellh/multistep"
 	packerssh "github.com/mitchellh/packer/communicator/ssh"
 	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/agent"
 )
 
 // CommHost looks up the host for the communicator.
@@ -63,8 +66,26 @@ func CommHost(
 // SSHConfig returns a function that can be used for the SSH communicator
 // config for connecting to the instance created over SSH using a private key
 // or a password.
-func SSHConfig(username, password string) func(multistep.StateBag) (*ssh.ClientConfig, error) {
+func SSHConfig(useAgent bool, username, password string) func(multistep.StateBag) (*ssh.ClientConfig, error) {
 	return func(state multistep.StateBag) (*ssh.ClientConfig, error) {
+		if useAgent {
+			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)
+			}
+
+			return &ssh.ClientConfig{
+				User: username,
+				Auth: []ssh.AuthMethod{
+					ssh.PublicKeysCallback(agent.NewClient(sshAgent).Signers),
+				},
+			}, nil
+		}
 
 		privateKey, hasKey := state.GetOk("privateKey")
 

website/source/docs/builders/openstack.html.md

@@ -147,6 +147,12 @@ builder.
     [`ssh_private_key_file`](/docs/templates/communicator.html#ssh_private_key_file)
     must be specified with this.
 
+-   `ssh_agent_auth` (boolean) - If true, the local SSH agent will be used to
+    authenticate connections to the source instance. No temporary key pair will
+    be used, and the values of `ssh_password` and `ssh_private_key_file` will
+    be ignored. Useful for when a temporary keypair can't be used, or when using
+    a certificate authority for SSH authentication.
+
 -   `tenant_id` or `tenant_name` (string) - The tenant ID or name to boot the
     instance into. Some OpenStack installations require this. If not specified,
     Packer will use the environment variable `OS_TENANT_NAME`, if set. Tenant