fix(ssh): unable to pass a custom HostKeyCallback func

Don't overwrite HostKeyCallback if one is provided.

Fixes: c35b808 ("plumbing: transport/ssh, auto-populate ClientConfig.HostKeyAlgorithms. Fixes go-git#411")
Fixes: go-git#654
Signed-off-by: Ayman Bagabas <ayman.bagabas@gmail.com>

plumbing/transport/ssh/auth_method.go

@@ -43,6 +43,7 @@ const (
 type KeyboardInteractive struct {
 	User      string
 	Challenge ssh.KeyboardInteractiveChallenge
+	HostKeyCallbackHelper
 }
 
 func (a *KeyboardInteractive) Name() string {
@@ -54,18 +55,19 @@ func (a *KeyboardInteractive) String() string {
 }
 
 func (a *KeyboardInteractive) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{
 			a.Challenge,
 		},
-	}, nil
+	})
 }
 
 // Password implements AuthMethod by using the given password.
 type Password struct {
 	User     string
 	Password string
+	HostKeyCallbackHelper
 }
 
 func (a *Password) Name() string {
@@ -77,17 +79,18 @@ func (a *Password) String() string {
 }
 
 func (a *Password) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.Password(a.Password)},
-	}, nil
+	})
 }
 
 // PasswordCallback implements AuthMethod by using a callback
 // to fetch the password.
 type PasswordCallback struct {
 	User     string
 	Callback func() (pass string, err error)
+	HostKeyCallbackHelper
 }
 
 func (a *PasswordCallback) Name() string {
@@ -99,16 +102,17 @@ func (a *PasswordCallback) String() string {
 }
 
 func (a *PasswordCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)},
-	}, nil
+	})
 }
 
 // PublicKeys implements AuthMethod by using the given key pairs.
 type PublicKeys struct {
 	User   string
 	Signer ssh.Signer
+	HostKeyCallbackHelper
 }
 
 // NewPublicKeys returns a PublicKeys from a PEM encoded private key. An
@@ -147,10 +151,10 @@ func (a *PublicKeys) String() string {
 }
 
 func (a *PublicKeys) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PublicKeys(a.Signer)},
-	}, nil
+	})
 }
 
 func username() (string, error) {
@@ -173,6 +177,7 @@ func username() (string, error) {
 type PublicKeysCallback struct {
 	User     string
 	Callback func() (signers []ssh.Signer, err error)
+	HostKeyCallbackHelper
 }
 
 // NewSSHAgentAuth returns a PublicKeysCallback based on a SSH agent, it opens
@@ -207,10 +212,10 @@ func (a *PublicKeysCallback) String() string {
 }
 
 func (a *PublicKeysCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return &ssh.ClientConfig{
+	return a.SetHostKeyCallback(&ssh.ClientConfig{
 		User: a.User,
 		Auth: []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)},
-	}, nil
+	})
 }
 
 // NewKnownHostsCallback returns ssh.HostKeyCallback based on a file based on a
@@ -286,9 +291,6 @@ func filterKnownHostsFiles(files ...string) ([]string, error) {
 
 // HostKeyCallbackHelper is a helper that provides common functionality to
 // configure HostKeyCallback into a ssh.ClientConfig.
-// Deprecated in favor of SetConfigHostKeyFields (see common.go) which provides
-// a mechanism for also setting ClientConfig.HostKeyAlgorithms for a specific
-// host.
 type HostKeyCallbackHelper struct {
 	// HostKeyCallback is the function type used for verifying server keys.
 	// If nil default callback will be create using NewKnownHostsCallback

plumbing/transport/ssh/common.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/go-git/go-git/v5/plumbing/transport"
 	"github.com/go-git/go-git/v5/plumbing/transport/internal/common"
+	"github.com/skeema/knownhosts"
 
 	"github.com/kevinburke/ssh_config"
 	"golang.org/x/crypto/ssh"
@@ -122,9 +123,11 @@ func (c *command) connect() error {
 		return err
 	}
 	hostWithPort := c.getHostWithPort()
-	config, err = SetConfigHostKeyFields(config, hostWithPort)
-	if err != nil {
-		return err
+	if config.HostKeyCallback != nil {
+		// Set the HostKeyAlgorithms based on HostKeyCallback.
+		// For background see https://github.com/go-git/go-git/issues/411 as well as
+		// https://github.com/golang/go/issues/29286 for root cause.
+		config.HostKeyAlgorithms = knownhosts.HostKeyAlgorithms(config.HostKeyCallback, hostWithPort)
 	}
 
 	overrideConfig(c.config, config)
@@ -167,23 +170,6 @@ func dial(network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
 	return ssh.NewClient(c, chans, reqs), nil
 }
 
-// SetConfigHostKeyFields sets cfg.HostKeyCallback and cfg.HostKeyAlgorithms
-// based on OpenSSH known_hosts. cfg is modified in-place. hostWithPort must be
-// supplied, since the algorithms will be set based on the known host keys for
-// that specific host. Otherwise, golang.org/x/crypto/ssh can return an error
-// upon connecting to a host whose *first* key is not known, even though other
-// keys (of different types) are known and match properly.
-// For background see https://github.com/go-git/go-git/issues/411 as well as
-// https://github.com/golang/go/issues/29286 for root cause.
-func SetConfigHostKeyFields(cfg *ssh.ClientConfig, hostWithPort string) (*ssh.ClientConfig, error) {
-	kh, err := newKnownHosts()
-	if err == nil {
-		cfg.HostKeyCallback = kh.HostKeyCallback()
-		cfg.HostKeyAlgorithms = kh.HostKeyAlgorithms(hostWithPort)
-	}
-	return cfg, err
-}
-
 func (c *command) getHostWithPort() string {
 	if addr, found := c.doGetHostWithPortFromSSHConfig(); found {
 		return addr