Comment 1 for bug 1298135

Rescope of a token does not extend its expiry time, so I'm not sure there's an existing keystone API we can use.

There's a second problem for backups initiated from Horizon, in that Horizon invalidates tokens on log-out or project switch, so in its case the problem is even worse.

You might be able to use keystone trusts to extend a token, but that is outside of the intended use-case for trusts.