vaultsubst

vaultsubst is a tool for injecting and optionally formatting vault KV secrets into files. It acts similarly to envsubst, but instead of environment variables it uses vault secrets. This is primarily useful if you have a large number of arbitrary KV-paths that you want to query and don't necessarily know ahead of time and/or are unable to set environment variables. It works by extracting structured strings out of an input file which are then used to query and finally inject the correct secret into the file (more precisely, stdout by default).

vaultsubst also supports basic formatting options which are applied sequentially to each secret prior to injection. The following transformations are currently supported:

• upper: convert secret to uppercase
• lower: convert secret to lowercase
• base64: encode in base64
• base64d: decode from base64
• trim: trim leading and trailing white-spaces

As it is quite common that secrets are stored in base64, an additional option b64 can be supplied separately from transform to indicate that the fetched secret should be decoded as such once fetched (this is equivalent to specifying transform=base64d).

Install

go install github.com/toalaah/vaultsubst@latest

Example

$ cat test.yml
apiVersion: v1
data:
  username: "@@path=kv/storage/postgres/creds,field=username,b64=true,transform=trim|upper@@"
  password: "@@path=kv/storage/postgres/creds,field=password@@"
  test: "static dont change"
kind: Secret
metadata:
  name: supersecretdata
type: Opaque

$ vaultsubst --delim=@@ test.yml
apiVersion: v1
data:
  username: "POSTGRES"
  password: "4_5tr0ng_4nd_c0mpl1c4t3d_p455w0rd"
  test: "static dont change"
kind: Secret
metadata:
  name: supersecretdata
type: Opaque

Interacting with KVv1 Backends

vaultsubst supports fetching secrets from both KVv1 and KVv2 stores. By default, a v2 backend is assumed, but this behavior can be overwritten on a per-secret basis by specifying ver=v1 in the template string, for example: @@path=kv1/storage/postgres/creds,field=username,ver=v1@@

Contributing

Contributions (PRs, issues, etc.) are welcome. Please note that the minimum required Go version for building vaultsubst is 1.22. Only the last two major Go versions are officially supported and tested against CI, as such there are no guarantees for any older versions.

License

This project is licensed under the terms of the MIT license.