plumbing: transport/ssh, Optional configuration of ssh.ClientConfig f…

…rom environment variables. Fixes go-git#411

plumbing/transport/ssh/auth_method.go

@@ -56,12 +56,10 @@ func (a *KeyboardInteractive) String() string {
 }
 
 func (a *KeyboardInteractive) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
-		User: a.User,
-		Auth: []ssh.AuthMethod{
-			a.Challenge,
-		},
-	})
+	clientConfig := DefaultSSHClientConfig
+	clientConfig.User = a.User
+	clientConfig.Auth = []ssh.AuthMethod{a.Challenge}
+	return a.SetHostKeyCallback(clientConfig)
 }
 
 // Password implements AuthMethod by using the given password.
@@ -80,10 +78,10 @@ func (a *Password) String() string {
 }
 
 func (a *Password) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
-		User: a.User,
-		Auth: []ssh.AuthMethod{ssh.Password(a.Password)},
-	})
+	clientConfig := DefaultSSHClientConfig
+	clientConfig.User = a.User
+	clientConfig.Auth = []ssh.AuthMethod{ssh.Password(a.Password)}
+	return a.SetHostKeyCallback(clientConfig)
 }
 
 // PasswordCallback implements AuthMethod by using a callback
@@ -103,10 +101,10 @@ func (a *PasswordCallback) String() string {
 }
 
 func (a *PasswordCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
-		User: a.User,
-		Auth: []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)},
-	})
+	clientConfig := DefaultSSHClientConfig
+	clientConfig.User = a.User
+	clientConfig.Auth = []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)}
+	return a.SetHostKeyCallback(clientConfig)
 }
 
 // PublicKeys implements AuthMethod by using the given key pairs.
@@ -152,10 +150,10 @@ func (a *PublicKeys) String() string {
 }
 
 func (a *PublicKeys) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
-		User: a.User,
-		Auth: []ssh.AuthMethod{ssh.PublicKeys(a.Signer)},
-	})
+	clientConfig := DefaultSSHClientConfig
+	clientConfig.User = a.User
+	clientConfig.Auth = []ssh.AuthMethod{ssh.PublicKeys(a.Signer)}
+	return a.SetHostKeyCallback(clientConfig)
 }
 
 func username() (string, error) {
@@ -213,10 +211,10 @@ func (a *PublicKeysCallback) String() string {
 }
 
 func (a *PublicKeysCallback) ClientConfig() (*ssh.ClientConfig, error) {
-	return a.SetHostKeyCallback(&ssh.ClientConfig{
-		User: a.User,
-		Auth: []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)},
-	})
+	clientConfig := DefaultSSHClientConfig
+	clientConfig.User = a.User
+	clientConfig.Auth = []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)}
+	return a.SetHostKeyCallback(clientConfig)
 }
 
 // NewKnownHostsCallback returns ssh.HostKeyCallback based on a file based on a

plumbing/transport/ssh/common.go

@@ -4,6 +4,7 @@ package ssh
 import (
 	"context"
 	"fmt"
+	"os"
 	"reflect"
 	"strconv"
 	"strings"
@@ -27,6 +28,89 @@ type sshConfig interface {
 	Get(alias, key string) string
 }
 
+// ENV_SSH_HOSTKEY_ALGORITHMS
+//
+// ssh.ClientConfig.HostKeyAlgorithms
+//
+// Use comma as separator if multiple values.
+//
+// Example:
+// export GO_GIT_SSH_HOSTKEY_ALGORITHMS="ssh-ed25519,ecdsa-sha2-nistp256"
+//
+// See golang.org/x/crypto/ssh for valid values.
+//
+//
+//
+const ENV_SSH_HOSTKEY_ALGORITHMS = "GO_GIT_SSH_HOSTKEY_ALGORITHMS"
+
+// ENV_SSH_CONFIG_KEY_EXCHANGES
+//
+// ssh.ClientConfig.Config.KeyExchanges
+//
+// Use comma as separator if multiple values.
+//
+// Example:
+// export GO_GIT_SSH_CONFIG_KEY_EXCHANGES="diffie-hellman-group14-sha1,ecdh-sha2-nistp256"
+//
+// See golang.org/x/crypto/ssh for valid values.
+const ENV_SSH_CONFIG_KEY_EXCHANGES = "GO_GIT_SSH_CONFIG_KEY_EXCHANGES"
+
+// ENV_SSH_CONFIG_CIPHERS
+//
+// ssh.ClientConfig.Config.Ciphers
+//
+// Use comma as separator if multiple values.
+//
+// Example:
+// export GO_GIT_SSH_CONFIG_CIPHERS="aes128-ctr,aes192-ctr"
+//
+// See golang.org/x/crypto/ssh for valid values.
+const ENV_SSH_CONFIG_CIPHERS = "GO_GIT_SSH_CONFIG_CIPHERS"
+
+// ENV_SSH_CONFIG_MACS
+//
+// ssh.ClientConfig.Config.MACs
+//
+// Use comma as separator if multiple values.
+//
+// Example:
+// export GO_GIT_SSH_CONFIG_MACS="hmac-sha2-256,hmac-sha1"
+//
+// See golang.org/x/crypto/ssh for valid values.
+const ENV_SSH_CONFIG_MACS = "GO_GIT_SSH_CONFIG_MACS"
+
+// DefaultSSHClientConfig
+//
+// The following environment variables will be used if defined
+//
+// GO_GIT_SSH_HOSTKEY_ALGORITHMS
+// GO_GIT_SSH_CONFIG_KEY_EXCHANGES
+// GO_GIT_SSH_CONFIG_CIPHERS
+// GO_GIT_SSH_CONFIG_MACS
+//
+var DefaultSSHClientConfig *ssh.ClientConfig = func() *ssh.ClientConfig {
+	sshClientConfig := &ssh.ClientConfig{}
+
+	if hostKeyAlgorithms, isSet := os.LookupEnv(ENV_SSH_HOSTKEY_ALGORITHMS); isSet {
+		// TODO validation
+		sshClientConfig.HostKeyAlgorithms = strings.Split(hostKeyAlgorithms, ",")
+	}
+	if keyExchanges, isSet := os.LookupEnv(ENV_SSH_CONFIG_KEY_EXCHANGES); isSet {
+		// TODO validation
+		sshClientConfig.Config.KeyExchanges = strings.Split(keyExchanges, ",")
+	}
+	if ciphers, isSet := os.LookupEnv(ENV_SSH_CONFIG_CIPHERS); isSet {
+		// TODO validation
+		sshClientConfig.Config.Ciphers = strings.Split(ciphers, ",")
+	}
+	if MACs, isSet := os.LookupEnv(ENV_SSH_CONFIG_MACS); isSet {
+		// TODO validation
+		sshClientConfig.Config.MACs = strings.Split(MACs, ",")
+	}
+
+	return sshClientConfig
+}()
+
 // NewClient creates a new SSH client with an optional *ssh.ClientConfig.
 func NewClient(config *ssh.ClientConfig) transport.Transport {
 	return common.NewClient(&runner{config: config})