dropbox: enable short lived access tokens #4792

Starting September 30th, 2021, the Dropbox OAuth flow will no longer
return long-lived access tokens. It will instead return short-lived
access tokens, and optionally return refresh tokens.

This patch adds the token_access_type=offline parameter which causes
dropbox to return short lived tokens now.

backend/dropbox/dropbox.go

@@ -125,6 +125,9 @@ func init() {
 		Config: func(ctx context.Context, name string, m configmap.Mapper) {
 			opt := oauthutil.Options{
 				NoOffline: true,
+				OAuth2Opts: []oauth2.AuthCodeOption{
+					oauth2.SetAuthURLParam("token_access_type", "offline"),
+				},
 			}
 			err := oauthutil.Config(ctx, "dropbox", name, m, dropboxConfig, &opt)
 			if err != nil {