Signer from Settings #1216
Description
With the new Settings configuration effort, we can new define all the values needed for a signer in the settings, so there is no longer a need to pass them separately in Signer::from_info or other methods. We could also handle CAWG signing in the same way. If you have specified CAWG configuration info for than we could automatically create a cawg signer from those settings. This vastly simplifies the API and examples. We would just need to call something like signer = Signer::from_settings(), and then pass that signer to our Builder signing method.
The settings can also allow for a remote signer URL. I'm thinking this could replace the current callback signer function, or at least leverage it. The idea is that there would be a standard protocol for calling a simple signer similar to what we have done for the callback API. But it would call a service. That service could be local or remote.
It would also be possible to directly support an HSA this way, but that might be better wrapped in a Rest API.