Key material should be able to be stored in a database

[aspnet-hello]

From @GrabYourPitchforks on Tuesday, October 28, 2014 6:27:46 PM

This would be implemented as an additional IXmlRepository.

Copied from original issue: aspnet/DataProtection#37

[aspnet-hello]

From @GrabYourPitchforks on Saturday, February 28, 2015 12:40:41 AM

Very difficult to make this generic - might be better as a sample? Can we do what Identity does for generic DB access?

[aspnet-hello]

From @muratg on Thursday, July 23, 2015 11:37:09 AM

Maybe better to have this as a sample.

[natemcmaster]

Closing as a duplicate of #2505. We have a PR in the works to add this. See aspnet/DataProtection#303