Initial commit: OpenVPN Manager v1.0

OpenVPN Web management console with multi-instance support, client cert
issuance, traffic/connection auditing, certificate expiry reminders,
auto backup/restore.

Stack:
- Backend: Go 1.21+ (Gin + JWT)
- Frontend: Vue 3 + Element Plus + ECharts + Vite
- Storage: JSON file (db.json) + filesystem (pki/, instances/, clients/, backups/)

Features:
- Multi-instance OpenVPN management (independent port/proto/subnet/PKI)
- One-click client certificate issuance with .ovpn (embedded certs)
- Certificate expiry reminders (30-day threshold)
- Connection log parsing (status-version 3)
- Auto backup/restore (tar.gz)
- Audit log for all write operations
- JWT auth (12h TTL)
- One-line install.sh for Ubuntu/Debian/RHEL/Fedora

backend/internal/middleware/auth.go

@@ -0,0 +1,57 @@
+package middleware
+
+import (
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/golang-jwt/jwt/v5"
+)
+
+type Claims struct {
+	Username string `json:"username"`
+	Role     string `json:"role"`
+	jwt.RegisteredClaims
+}
+
+func IssueToken(secret, username, role string, ttl time.Duration) (string, error) {
+	c := Claims{
+		Username: username,
+		Role:     role,
+		RegisteredClaims: jwt.RegisteredClaims{
+			ExpiresAt: jwt.NewNumericDate(time.Now().Add(ttl)),
+			IssuedAt:  jwt.NewNumericDate(time.Now()),
+		},
+	}
+	t := jwt.NewWithClaims(jwt.SigningMethodHS256, c)
+	return t.SignedString([]byte(secret))
+}
+
+func JWTAuth(secret string) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		h := c.GetHeader("Authorization")
+		if h == "" {
+			h = c.Query("token")
+		}
+		const prefix = "Bearer "
+		if strings.HasPrefix(h, prefix) {
+			h = strings.TrimPrefix(h, prefix)
+		}
+		if h == "" {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "missing token"})
+			return
+		}
+		claims := &Claims{}
+		_, err := jwt.ParseWithClaims(h, claims, func(t *jwt.Token) (interface{}, error) {
+			return []byte(secret), nil
+		})
+		if err != nil {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "invalid token"})
+			return
+		}
+		c.Set("user", claims.Username)
+		c.Set("role", claims.Role)
+		c.Next()
+	}
+}