[1] Final: OpenID Connect Core 1.0 incorporating errata set 1 ( 版) <http://openid.net/specs/openid-connect-core-1_0.html#OfflineAccess>
[2] OpenID Connect (OAuth 2.0 for Login) - Google Accounts Authentication and Authorization — Google Developers ( 版) <https://developers.google.com/accounts/docs/OpenIDConnect#refresh-tokens>
[3] OpenID Connect (OAuth 2.0 for Login) - Google Accounts Authentication and Authorization — Google Developers ( 版) <https://developers.google.com/accounts/docs/OpenIDConnect#authenticationuriparameters>
The allowed values are offline and online. The effect is documented in Offline Access; if an access token is being requested, the client does not receive a refresh token unless offline is specified.
[4] Using OAuth 2.0 for Web Server Applications - Google Accounts Authentication and Authorization — Google Developers ( 版) <https://developers.google.com/accounts/docs/OAuth2WebServer#offline>