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
One thing that has been a point of confusion for users is Vault's
response when deleting a key that does not actually exist in the system.
For example, consider:
$ vault delete secret/foo
Success! Deleted 'secret/foo'
This message is misleading if the secret does not exist, especially if
the same command is run twice in a row.
Obviously the reason for this is clear - returning an error if a secret
does not exist would reveal the existence of a secret (the same reason
everything on S3 is a 403 or why GitHub repos 404 instead of 403 if you
do not have permission to view them).
I think we can make the UX a little bit better by adding just a few
words to the output:
$ vault delete secret/foo
Success! Deleted 'secret/foo' if it existed
This makes it clear that the operation was only performed if the secret
existed, but it does not reveal any more information.
