This is a hook script written in rust used for dns challenge verification of certificates with linode, as per: https://github.com/dehydrated-io/dehydrated/blob/master/docs/dns-verification.md

Assuming you have rust installed you will need to clone the repo and create a folder .cargo with the file config.toml inside it. In this file add an environment variable with your API key (get it here: https://www.linode.com/docs/products/tools/api/get-started/#get-an-access-token).

for example:

[env]
API_KEY = "64characterAPIkeygoeshere"

As each dns challenge will take at least a few minutes it is HIGHLY recommended to set HOOKCHAIN=yes (see https://github.com/dehydrated-io/dehydrated/blob/master/docs/hook_chain.md) inside your dehydrated config, otherwise you're in for a long wait if you've a lot of domains to certify.