How can I verify user token on golang server or atlas function

I send the token of a registered user from Unity to my socket server(golang). How can I verify that the player is a valid Realm user? Alternatively, can my socket server make a POST request to an Atlas function for verification?

Unity

        public static async Task<string> GetValidAccessToken() {
            await MyApp.CurrentUser.RefreshCustomDataAsync();
            return MyApp.CurrentUser.AccessToken;
        }