Add JWT authorization functionality.

internal/auth/jwt.go

@@ -0,0 +1,64 @@
+package auth
+
+import (
+	"errors"
+	"os"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+)
+
+type Claims struct {
+	Username string `json:"username"`
+	jwt.RegisteredClaims
+}
+
+func secret() ([]byte, error) {
+	s := os.Getenv("JWT_SECRET")
+	if s == "" {
+		return nil, errors.New("JWT_SECRET is not set")
+	}
+	return []byte(s), nil
+}
+
+func NewAccessToken(username string, ttl time.Duration) (string, error) {
+	key, err := secret()
+	if err != nil {
+		return "", err
+	}
+	now := time.Now()
+	claims := Claims{
+		Username: username,
+		RegisteredClaims: jwt.RegisteredClaims{
+			Subject:   username,
+			IssuedAt:  jwt.NewNumericDate(now),
+			ExpiresAt: jwt.NewNumericDate(now.Add(ttl)),
+		},
+	}
+
+	t := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+	return t.SignedString(key)
+}
+
+func ParseAccessToken(tokenString string) (*Claims, error) {
+	key, err := secret()
+	if err != nil {
+		return nil, err
+	}
+
+	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (any, error) {
+		return key, nil
+	},
+		jwt.WithValidMethods([]string{jwt.SigningMethodHS256.Alg()}),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	claims, ok := token.Claims.(*Claims)
+	if !ok || !token.Valid {
+		return nil, errors.New("invalid token")
+	}
+
+	return claims, nil
+}

internal/auth/middleware.go

@@ -0,0 +1,41 @@
+package auth
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+const CtxUsernameKey = "username"
+
+func Middleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		h := c.GetHeader("Authorization")
+		if h == "" {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "missing Authorization header"})
+			return
+		}
+
+		const prefix = "Bearer "
+		if !strings.HasPrefix(h, prefix) {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "expected Bearer token"})
+			return
+		}
+
+		raw := strings.TrimSpace(strings.TrimPrefix(h, prefix))
+		if raw == "" {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "empty token"})
+			return
+		}
+
+		claims, err := ParseAccessToken(raw)
+		if err != nil {
+			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "invalid token"})
+			return
+		}
+
+		c.Set(CtxUsernameKey, claims.Username)
+		c.Next()
+	}
+}