Allow for additional Vault auth mechanisms.

[halcyondude]

We're using Vault, but not with the github auth plugin. This issue is to float the idea of enabling/allowing for additional types of authentication w/ Vault.

The list supported by HashiCorp directly are here: https://www.vaultproject.io/docs/auth

In our specific case we are using:

https://github.com/jetstack/vault-plugin-auth-google

To auth via GSuite. We're prototyping options on a fork and would like to confirm that PR's are welcome to enable something like this.

Please advise and thanks!

[garetht]

Yup, that would be welcome!