mod_http_oauth2: Don't issue client_secret when not using authentication This is pretty much only for implicit flow, which is considered insecure anyway, so this is of limited value. If we delete all the implicit flow code, this could be reverted.

2c07bcf56a36d6e74dc0f5422e89bd61f4d31239 0.8-diverge
1656d4fd71d07aa3a52da89d4daf7723a555e7dd last-google-code-commit