[BACKEND] Initialize Go backend structure and dependencies (#23)

server/middleware/auth.go

@@ -0,0 +1,68 @@
+package middleware
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+	"github.com/golang-jwt/jwt/v5"
+
+	"git.gobha.me/xcaliber/chat-switchboard/config"
+	"git.gobha.me/xcaliber/chat-switchboard/database"
+)
+
+// Claims represents the JWT payload.
+type Claims struct {
+	UserID string `json:"user_id"`
+	Email  string `json:"email"`
+	jwt.RegisteredClaims
+}
+
+// Auth returns a Gin middleware that validates JWT bearer tokens.
+// When no database is connected (unmanaged mode), all requests
+// are allowed through without authentication.
+func Auth(cfg *config.Config) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		// Skip auth when running without a database (unmanaged mode)
+		if !database.IsConnected() {
+			c.Next()
+			return
+		}
+
+		header := c.GetHeader("Authorization")
+		if header == "" {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{
+				"error": "missing authorization header",
+			})
+			return
+		}
+
+		tokenString := strings.TrimPrefix(header, "Bearer ")
+		if tokenString == header {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{
+				"error": "invalid authorization format",
+			})
+			return
+		}
+
+		claims := &Claims{}
+		token, err := jwt.ParseWithClaims(tokenString, claims, func(t *jwt.Token) (interface{}, error) {
+			if _, ok := t.Method.(*jwt.SigningMethodHMAC); !ok {
+				return nil, jwt.ErrSignatureInvalid
+			}
+			return []byte(cfg.JWTSecret), nil
+		})
+
+		if err != nil || !token.Valid {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{
+				"error": "invalid or expired token",
+			})
+			return
+		}
+
+		// Store claims in context for downstream handlers
+		c.Set("user_id", claims.UserID)
+		c.Set("email", claims.Email)
+		c.Next()
+	}
+}