We have a standalone Java application (see "Installed application") which runs periodically and uses Google API (updates some information from customer databases/ldap/...).

To access Google APIs we store username and password in configuration file, which is a security risk and customer does not like that. So we would like to use OAuth2 long-living access token instead.

What`s default expiration time for Google OAuth2 access tokens ?

As we will have only access token in application, app itself cannot refresh it when access token expires.

Personally I think that OAuth2 implementation in this case will not bring any major benefit but let`s focus on main question - default expiration times.