Add support for using existing vault auto-auth configurations as the
provider configuration when using Vault's CA provider with AliCloud.
AliCloud requires 2 extra fields to enable it to use STS (it's preferred
auth setup). Our vault-plugin-auth-alicloud package contained a method
to help generate them as they require you to make an http call to
a faked endpoint proxy to get them (url and headers base64 encoded).
