Add ssh.AuthMethods for passing in custom authentication (#123)

* Add ssh.AuthMethods for passing in custom authentication

Signed-off-by: Kimmo Lehto <klehto@mirantis.com>

* Add a test for passing in a private key

Signed-off-by: Kimmo Lehto <klehto@mirantis.com>

---------

Signed-off-by: Kimmo Lehto <klehto@mirantis.com>

cmd/rigtest/rigtest.go

@@ -105,6 +105,7 @@ func main() {
 	pwd := flag.String("pass", "", "winrm password")
 	https := flag.Bool("https", false, "use https for winrm")
 	connectOnly := flag.Bool("connect", false, "just connect and quit")
+	sshKey := flag.String("ssh-private-key", "", "ssh private key")
 
 	fn := fmt.Sprintf("test_%s.txt", time.Now().Format("20060102150405"))
 
@@ -159,16 +160,34 @@ func main() {
 		var h *Host
 		switch *proto {
 		case "ssh":
-			h = &Host{
-				Connection: rig.Connection{
-					SSH: &rig.SSH{
-						Address:          address,
-						Port:             port,
-						User:             *usr,
-						KeyPath:          kp,
-						PasswordCallback: passfunc,
+			if *sshKey != "" {
+				// test with private key in a string
+				authM, err := rig.ParseSSHPrivateKey([]byte(*sshKey), rig.DefaultPasswordCallback)
+				if err != nil {
+					panic(err)
+				}
+				h = &Host{
+					Connection: rig.Connection{
+						SSH: &rig.SSH{
+							Address:     address,
+							Port:        port,
+							User:        *usr,
+							AuthMethods: authM,
+						},
 					},
-				},
+				}
+			} else {
+				h = &Host{
+					Connection: rig.Connection{
+						SSH: &rig.SSH{
+							Address:          address,
+							Port:             port,
+							User:             *usr,
+							KeyPath:          kp,
+							PasswordCallback: passfunc,
+						},
+					},
+				}
 			}
 		case "winrm":
 			h = &Host{

ssh.go

@@ -35,7 +35,15 @@ type SSH struct {
 	HostKey          string           `yaml:"hostKey,omitempty"`
 	Bastion          *SSH             `yaml:"bastion,omitempty"`
 	PasswordCallback PasswordCallback `yaml:"-"`
-	name             string
+
+	// AuthMethods can be used to pass in a list of ssh.AuthMethod objects
+	// for example to use a private key from memory:
+	//   ssh.PublicKeys(privateKey)
+	// For convenience, you can use ParseSSHPrivateKey() to parse a private key:
+	//   authMethods, err := rig.ParseSSHPrivateKey(key, rig.DefaultPassphraseCallback)
+	AuthMethods []ssh.AuthMethod `yaml:"-"`
+
+	name string
 
 	isWindows bool
 	knowOs    bool
@@ -338,7 +346,7 @@ func (c *SSH) hostkeyCallback() (ssh.HostKeyCallback, error) {
 	return knownhostsCallback(defaultPath, permissive, hash)
 }
 
-func (c *SSH) clientConfig() (*ssh.ClientConfig, error) {
+func (c *SSH) clientConfig() (*ssh.ClientConfig, error) { //nolint:cyclop
 	config := &ssh.ClientConfig{
 		User: c.User,
 	}
@@ -360,6 +368,11 @@ func (c *SSH) clientConfig() (*ssh.ClientConfig, error) {
 		}
 	}
 
+	if len(c.AuthMethods) > 0 {
+		log.Tracef("%s: using %d passed-in auth methods", c, len(c.AuthMethods))
+		config.Auth = c.AuthMethods
+	}
+
 	for _, keyPath := range c.keyPaths {
 		if am, ok := authMethodCache.Load(keyPath); ok {
 			switch authM := am.(type) {
@@ -695,3 +708,41 @@ func (c *SSH) ExecInteractive(cmd string) error {
 
 	return nil
 }
+
+// ParseSSHPrivateKey is a convenience utility to parses a private key and
+// return []ssh.AuthMethod to be used in SSH{} AuthMethods field. This
+// way you can avoid importing golang.org/x/crypto/ssh in your code
+// and handle the passphrase prompt in a callback function.
+func ParseSSHPrivateKey(key []byte, callback PasswordCallback) ([]ssh.AuthMethod, error) {
+	signer, err := ssh.ParsePrivateKey(key)
+	if err == nil {
+		return []ssh.AuthMethod{ssh.PublicKeys(signer)}, nil
+	}
+	var ppErr *ssh.PassphraseMissingError
+	if !errors.As(err, &ppErr) {
+		return nil, fmt.Errorf("failed to parse key: %w", err)
+	}
+	if callback == nil {
+		return nil, fmt.Errorf("key is encrypted and no callback provided: %w", err)
+	}
+	pass, err := callback()
+	if err != nil {
+		return nil, fmt.Errorf("failed to get passphrase: %w", err)
+	}
+	signer, err = ssh.ParsePrivateKeyWithPassphrase(key, []byte(pass))
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse key with passphrase: %w", err)
+	}
+	return []ssh.AuthMethod{ssh.PublicKeys(signer)}, nil
+}
+
+// DefaultPasswordCallback is a default implementation for PasswordCallback
+func DefaultPasswordCallback() (string, error) {
+	fmt.Print("Enter passphrase: ")
+	pass, err := term.ReadPassword(int(os.Stdin.Fd()))
+	fmt.Println()
+	if err != nil {
+		return "", fmt.Errorf("failed to read password: %w", err)
+	}
+	return string(pass), nil
+}

test/test.sh

@@ -170,6 +170,17 @@ rig_test_key_from_path() {
   RET=$exit_code
 }
 
+rig_test_key_from_memory() {
+  color_echo "- Testing connecting using a key from string"
+  make create-host
+  mv .ssh/identity .ssh/identity2
+  set +e
+  ./rigtest -host 127.0.0.1:$(ssh_port node0) -user root -ssh-private-key "$(cat .ssh/identity2)" -connect
+  local exit_code=$?
+  set -e
+  RET=$exit_code
+}
+
 rig_test_key_from_default_location() {
   color_echo "- Testing keypath from default location"
   make create-host