This removes all references I could find to:
- credential provider
- authentication backend
- authentication provider
- auth provider
- auth backend
in favor of the unified:
- auth method
Using the latest vault release, I was getting the following error when the policy used `write`:
Error: Error making API request.
URL: PUT http://0.0.0.0:8200/v1/sys/policy/secret
Code: 400. Errors:
* Failed to parse policy: path "secret/*": invalid capability 'write'
I think `create` is the correct new Capability.
