Renew token

[jl-wynen]

Tokens are only valid for 1h. But it is possible to get a new one while the current one is still valid. Client should automatically ask for a new one when needed.

Need to determine what triggers the renewal. E.g.:

1. Before or after any request.
2. Like 1 but only after some time has passed since the last one. What would that time be? 30min? 50min? Ultimately this depends on how often users make requests which we cannot predict.
3. Do it periodically. This would require a separate thread and would do HTTP requests without the user knowing. I'd avoid that. We should be explicit.
4. Require the user to do it. The user should definitely have the option to trigger renewal but for most use cases, this is unergonomic.