feat: new ValidateToken method for AuthService, based on code from the monolithic implementation of auth middleware;

feat: add detailed authentication error types;

backend/internal/services/auth.go

@@ -601,7 +601,85 @@ func (a *authServiceImpl) Refresh(request models.RefreshRequest) (*models.Refres
 	return nil, errs.ErrNotImplemented
 }
 
-func (a *authServiceImpl)	ValidateToken(token string, tokenType enums.JwtTokenType) (*dto.SessionInfo, error) {
+func (a *authServiceImpl)	ValidateToken(jwtToken string, tokenType enums.JwtTokenType) (*dto.SessionInfo, error) {
+
+	var err error
+
+	token, err := jwt.ParseWithClaims(
+		jwtToken, 
+		&dto.UserClaims{}, 
+		func(token *jwt.Token) (any, error) {
+			if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
+				return nil, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
+			}
+			return []byte(config.GetConfig().JwtSecret), nil
+		},
+	)
+
+	if err != nil {
+		if errors.Is(err, jwt.ErrTokenExpired) {
+			return nil, errs.ErrTokenExpired
+		} 
+		return nil, errs.ErrInvalidToken
+	}
+
+	if claims, ok := token.Claims.(*dto.UserClaims); ok && token.Valid {
+
+		if claims.Type != tokenType {
+			return nil, errs.ErrWrongTokenType
+		}
+
+		ctx := context.TODO()
+		isTerminated, redisErr := a.redis.Get(ctx, fmt.Sprintf("session::%s::is_terminated", claims.Session)).Bool()
+		if redisErr != nil && redisErr != redis.Nil {
+			a.log.Error(
+				"Failed to lookup cache to check whether session is not terminated",	
+				zap.Error(redisErr))
+			return nil, redisErr
+		}
+
+		// Cache if nil
+		if redisErr == redis.Nil {
+			db := database.NewDbHelper(a.dbctx)
+
+			session, err := db.Queries.GetSessionByGuid(db.CTX, claims.Session)
+			if err != nil {
+
+				if errors.Is(err, pgx.ErrNoRows) {
+					a.log.Warn(
+						"Session does not exist or was deleted",
+						zap.String("session", claims.Session))
+					return nil, errs.ErrSessionNotFound
+				}
+
+				a.log.Error(
+					"Failed to lookup session in database",	
+					zap.String("session", claims.Session),
+					zap.Error(err))
+				return nil, err
+			}
+
+			if err := a.redis.Set(
+				ctx, 
+				fmt.Sprintf("session::%s::is_terminated", claims.Session), 
+				session.Terminated, 
+				time.Duration(8 * time.Hour), // XXX: magic number
+			).Err(); err != nil {
+				a.log.Error(
+					"Failed to cache session's is_terminated state",	
+					zap.String("session", claims.Session),
+					zap.Error(err))
+				// c.AbortWithStatus(http.StatusInternalServerError)
+				return nil, err
+			}
+
+			isTerminated = *session.Terminated
+		}
+
+		if isTerminated {
+			return nil, errs.ErrSessionTerminated
+		}
+	}
 	return nil, errs.ErrNotImplemented
 }