fix: SSH does not try multiple authentication methods of the same type

Author: cgroschupp

ssh.go

@@ -58,7 +58,7 @@ type SSH struct {
 type PasswordCallback func() (secret string, err error)
 
 var (
-	authMethodCache   = sync.Map{}
+	signerCache       = sync.Map{}
 	defaultKeypaths   = []string{"~/.ssh/id_rsa", "~/.ssh/identity", "~/.ssh/id_dsa", "~/.ssh/id_ecdsa", "~/.ssh/id_ed25519"}
 	dummyhostKeyPaths []string
 	globalOnce        sync.Once
@@ -407,33 +407,33 @@ func (c *SSH) clientConfig() (*ssh.ClientConfig, error) { //nolint:cyclop
 		log.Tracef("%s: using %d passed-in auth methods", c, len(c.AuthMethods))
 		config.Auth = c.AuthMethods
 	} else if len(signers) > 0 {
-		log.Debugf("%s: using all keys (%d) from ssh agent because a keypath was not explicitly given", c, len(signers))
-		config.Auth = append(config.Auth, ssh.PublicKeys(signers...))
+		log.Debugf("%s: using all keys (%d) from ssh agent", c, len(signers))
 	}
 
 	for _, keyPath := range c.keyPaths {
-		if am, ok := authMethodCache.Load(keyPath); ok {
+		if am, ok := signerCache.Load(keyPath); ok {
 			switch authM := am.(type) {
-			case ssh.AuthMethod:
-				log.Tracef("%s: using cached auth method for %s", c, keyPath)
-				config.Auth = append(config.Auth, authM)
+			case ssh.Signer:
+				log.Tracef("%s: using cached signer for %s", c, keyPath)
+				signers = append(signers, authM)
 			case error:
 				log.Tracef("%s: already discarded key %s: %v", c, keyPath, authM)
 			default:
 				log.Tracef("%s: unexpected type %T for cached auth method for %s", c, am, keyPath)
 			}
 			continue
 		}
-		privateKeyAuth, err := c.pkeySigner(signers, keyPath)
+		signer, err := c.pkeySigner(signers, keyPath)
 		if err != nil {
 			log.Debugf("%s: failed to obtain a signer for identity %s: %v", c, keyPath, err)
 			// store the error so this key won't be loaded again
-			authMethodCache.Store(keyPath, err)
+			signerCache.Store(keyPath, err)
 		} else {
-			authMethodCache.Store(keyPath, privateKeyAuth)
-			config.Auth = append(config.Auth, privateKeyAuth)
+			signerCache.Store(keyPath, signer)
+			signers = append(signers, signer)
 		}
 	}
+	config.Auth = append(config.Auth, ssh.PublicKeys(signers...))
 
 	if len(config.Auth) == 0 {
 		return nil, fmt.Errorf("%w: no usable authentication method found", ErrCantConnect)
@@ -489,22 +489,22 @@ func (c *SSH) Connect() error {
 	return nil
 }
 
-func (c *SSH) pubkeySigner(signers []ssh.Signer, key ssh.PublicKey) (ssh.AuthMethod, error) {
+func (c *SSH) pubkeySigner(signers []ssh.Signer, key ssh.PublicKey) (ssh.Signer, error) {
 	if len(signers) == 0 {
 		return nil, fmt.Errorf("%w: signer not found for public key", ErrCantConnect)
 	}
 
 	for _, s := range signers {
 		if bytes.Equal(key.Marshal(), s.PublicKey().Marshal()) {
 			log.Debugf("%s: signer for public key available in ssh agent", c)
-			return ssh.PublicKeys(s), nil
+			return s, nil
 		}
 	}
 
 	return nil, fmt.Errorf("%w: the provided key is a public key and is not known by agent", ErrAuthFailed)
 }
 
-func (c *SSH) pkeySigner(signers []ssh.Signer, path string) (ssh.AuthMethod, error) {
+func (c *SSH) pkeySigner(signers []ssh.Signer, path string) (ssh.Signer, error) {
 	log.Tracef("%s: checking identity file %s", c, path)
 	key, err := os.ReadFile(path)
 	if err != nil {
@@ -520,7 +520,7 @@ func (c *SSH) pkeySigner(signers []ssh.Signer, path string) (ssh.AuthMethod, err
 	signer, err := ssh.ParsePrivateKey(key)
 	if err == nil {
 		log.Debugf("%s: using an unencrypted private key from %s", c, path)
-		return ssh.PublicKeys(signer), nil
+		return signer, nil
 	}
 
 	var ppErr *ssh.PassphraseMissingError
@@ -543,7 +543,7 @@ func (c *SSH) pkeySigner(signers []ssh.Signer, path string) (ssh.AuthMethod, err
 			if err != nil {
 				return nil, fmt.Errorf("%w: protected key %s decoding failed: %w", ErrCantConnect, path, err)
 			}
-			return ssh.PublicKeys(signer), nil
+			return signer, nil
 		}
 	}