1. login
2. request email permission
std::vector<std::string> permissions;
permissions.push_back(FB_PERM_READ_EMAIL);
PluginFacebook::requestReadPermissions(permissions);
3. request
PluginFacebook::FBAPIParam params;
params["fields"] = "name,email";
PluginFacebook::api("me", "GET", params, "your_tag_id");