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package ssh
import (
"errors"
"fmt"
"net"
"os"
"os/user"
"path/filepath"
"golang.org/x/crypto/ssh"
"golang.org/x/crypto/ssh/agent"
"golang.org/x/crypto/ssh/knownhosts"
)
var ErrEmptySSHAgentAddr = errors.New("SSH_AUTH_SOCK env variable is required")
// AuthMethod is the interface all auth methods for the ssh client
// must implement. The clientConfig method returns the ssh client
// configuration needed to establish an ssh connection.
type AuthMethod interface {
clientConfig() *ssh.ClientConfig
hostKeyCallback() (ssh.HostKeyCallback, error)
}
// The names of the AuthMethod implementations. To be returned by the
// Name() method. Most git servers only allow PublicKeysName and
// PublicKeysCallbackName.
const (
KeyboardInteractiveName = "ssh-keyboard-interactive"
PasswordName = "ssh-password"
PasswordCallbackName = "ssh-password-callback"
PublicKeysName = "ssh-public-keys"
PublicKeysCallbackName = "ssh-public-key-callback"
)
// KeyboardInteractive implements AuthMethod by using a
// prompt/response sequence controlled by the server.
type KeyboardInteractive struct {
User string
Challenge ssh.KeyboardInteractiveChallenge
baseAuthMethod
}
func (a *KeyboardInteractive) Name() string {
return KeyboardInteractiveName
}
func (a *KeyboardInteractive) String() string {
return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
}
func (a *KeyboardInteractive) clientConfig() *ssh.ClientConfig {
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.KeyboardInteractiveChallenge(a.Challenge)},
}
}
// Password implements AuthMethod by using the given password.
type Password struct {
User string
Pass string
baseAuthMethod
}
func (a *Password) Name() string {
return PasswordName
}
func (a *Password) String() string {
return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
}
func (a *Password) clientConfig() *ssh.ClientConfig {
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.Password(a.Pass)},
}
}
// PasswordCallback implements AuthMethod by using a callback
// to fetch the password.
type PasswordCallback struct {
User string
Callback func() (pass string, err error)
baseAuthMethod
}
func (a *PasswordCallback) Name() string {
return PasswordCallbackName
}
func (a *PasswordCallback) String() string {
return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
}
func (a *PasswordCallback) clientConfig() *ssh.ClientConfig {
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.PasswordCallback(a.Callback)},
}
}
// PublicKeys implements AuthMethod by using the given
// key pairs.
type PublicKeys struct {
User string
Signer ssh.Signer
baseAuthMethod
}
func (a *PublicKeys) Name() string {
return PublicKeysName
}
func (a *PublicKeys) String() string {
return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
}
func (a *PublicKeys) clientConfig() *ssh.ClientConfig {
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.PublicKeys(a.Signer)},
}
}
// PublicKeysCallback implements AuthMethod by asking a
// ssh.agent.Agent to act as a signer.
type PublicKeysCallback struct {
User string
Callback func() (signers []ssh.Signer, err error)
baseAuthMethod
}
func (a *PublicKeysCallback) Name() string {
return PublicKeysCallbackName
}
func (a *PublicKeysCallback) String() string {
return fmt.Sprintf("user: %s, name: %s", a.User, a.Name())
}
func (a *PublicKeysCallback) clientConfig() *ssh.ClientConfig {
return &ssh.ClientConfig{
User: a.User,
Auth: []ssh.AuthMethod{ssh.PublicKeysCallback(a.Callback)},
}
}
const DefaultSSHUsername = "git"
// NewSSHAgentAuth opens a pipe with the SSH agent and uses the pipe
// as the implementer of the public key callback function.
func NewSSHAgentAuth(user string) (*PublicKeysCallback, error) {
if user == "" {
user = DefaultSSHUsername
}
sshAgentAddr := os.Getenv("SSH_AUTH_SOCK")
if sshAgentAddr == "" {
return nil, ErrEmptySSHAgentAddr
}
pipe, err := net.Dial("unix", sshAgentAddr)
if err != nil {
return nil, fmt.Errorf("error connecting to SSH agent: %q", err)
}
return &PublicKeysCallback{
User: user,
Callback: agent.NewClient(pipe).Signers,
}, nil
}
// NewKnownHostsCallback returns ssh.HostKeyCallback based on a file based on a
// know_hosts file. http://man.openbsd.org/sshd#SSH_KNOWN_HOSTS_FILE_FORMAT
//
// If files is empty, the list of files will be read from the SSH_KNOWN_HOSTS
// environment variable, example:
// /home/foo/custom_known_hosts_file:/etc/custom_known/hosts_file
//
// If SSH_KNOWN_HOSTS is not set the following file locations will be used:
// ~/.ssh/known_hosts
// /etc/ssh/ssh_known_hosts
func NewKnownHostsCallback(files ...string) (ssh.HostKeyCallback, error) {
files, err := getDefaultKnownHostsFiles()
if err != nil {
return nil, err
}
files, err = filterKnownHostsFiles(files...)
if err != nil {
return nil, err
}
return knownhosts.New(files...)
}
func getDefaultKnownHostsFiles() ([]string, error) {
files := filepath.SplitList(os.Getenv("SSH_KNOWN_HOSTS"))
if len(files) != 0 {
return files, nil
}
user, err := user.Current()
if err != nil {
return nil, err
}
return []string{
filepath.Join(user.HomeDir, "/.ssh/known_hosts"),
"/etc/ssh/ssh_known_hosts",
}, nil
}
func filterKnownHostsFiles(files ...string) ([]string, error) {
var out []string
for _, file := range files {
_, err := os.Stat(file)
if err == nil {
out = append(out, file)
continue
}
if !os.IsNotExist(err) {
return nil, err
}
}
if len(out) == 0 {
return nil, fmt.Errorf("unable to find any valid know_hosts file, set SSH_KNOWN_HOSTS env variable")
}
return out, nil
}
type baseAuthMethod struct {
// HostKeyCallback is the function type used for verifying server keys.
// If nil default callback will be create using NewKnownHostsHostKeyCallback
// without argument.
HostKeyCallback ssh.HostKeyCallback
}
func (m *baseAuthMethod) hostKeyCallback() (ssh.HostKeyCallback, error) {
if m.HostKeyCallback == nil {
return NewKnownHostsCallback()
}
return m.HostKeyCallback, nil
}
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