auth_proxy: non-negative cache TTL (#17495)

fixes setex error with redis on #17377

(cherry picked from commit 826d33ea37)

pkg/middleware/auth_proxy/auth_proxy.go

@@ -311,7 +311,7 @@ func (auth *AuthProxy) Remember(id int64) *Error {
 		return nil
 	}
 
-	expiration := time.Duration(-auth.cacheTTL) * time.Minute
+	expiration := time.Duration(auth.cacheTTL) * time.Minute
 
 	err = auth.store.Set(key, id, expiration)
 	if err != nil {