feat: ssh client implement (#3671)

* feat: frps support ssh

* fix: comments

* fix: update pkg

* fix: remove useless change

---------

Co-authored-by: int7 <int7@gmail.com>

pkg/config/v1/ssh.go

@@ -0,0 +1,72 @@
+package v1
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/crypto/ssh"
+)
+
+const (
+	// custom define
+	SSHClientLoginUserPrefix = "_frpc_ssh_client_"
+)
+
+// encodePrivateKeyToPEM encodes Private Key from RSA to PEM format
+func GeneratePrivateKey() ([]byte, error) {
+	privateKey, err := generatePrivateKey()
+	if err != nil {
+		return nil, errors.New("gen private key error")
+	}
+
+	privBlock := pem.Block{
+		Type:    "RSA PRIVATE KEY",
+		Headers: nil,
+		Bytes:   x509.MarshalPKCS1PrivateKey(privateKey),
+	}
+
+	return pem.EncodeToMemory(&privBlock), nil
+}
+
+// generatePrivateKey creates a RSA Private Key of specified byte size
+func generatePrivateKey() (*rsa.PrivateKey, error) {
+	privateKey, err := rsa.GenerateKey(rand.Reader, 4096)
+	if err != nil {
+		return nil, err
+	}
+
+	err = privateKey.Validate()
+	if err != nil {
+		return nil, err
+	}
+	return privateKey, nil
+}
+
+func LoadSSHPublicKeyFilesInDir(dirPath string) (map[string]ssh.PublicKey, error) {
+	fileMap := make(map[string]ssh.PublicKey)
+	files, err := os.ReadDir(dirPath)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, file := range files {
+		filePath := filepath.Join(dirPath, file.Name())
+		content, err := os.ReadFile(filePath)
+		if err != nil {
+			return nil, err
+		}
+
+		parsedAuthorizedKey, _, _, _, err := ssh.ParseAuthorizedKey(content)
+		if err != nil {
+			continue
+		}
+		fileMap[ssh.FingerprintSHA256(parsedAuthorizedKey)] = parsedAuthorizedKey
+	}
+
+	return fileMap, nil
+}