An Elixir library to manage secrets, with the possibily to watch for their changes on filesystem.

Thereafter, watched secrets are the secrets read from the filesystem, while in-memory secrets are secrets which do not have a corresponding file.

As per the recommandation of the EEF Security Workgroup, secrets are passed around as closures.

def deps do
  [
    {:secret_agent, "~> 0.8"}
  ]
end

1. Establish the list of initial secrets:

   secrets =
     %{
       "credentials" => [value: "super-secret"],
       "secret.txt" => [
         directory: "path/to/secrets/directory",
         init_callback: fn wrapped_secret-> do_something_with_secret(wrapped_secret) end,
         callback: fn wrapped_secret-> do_something_with_secret(wrapped_secret) end
       ],
       "sub/path/secret.txt" => [
         directory: "path/to/secrets/directory"
       ]
     }

   ℹ️ When using the :directory option, the name of the secret is the name of the file to watch in the directory. The secret will be loaded from the file upon startup. It this option is not set, the secret is considered to be an in-memory secret.

   ℹ️ The :init_callback option specifies a callback that will be invoked the first time the watched secret is read from disk. Default to a function with no effect.

   ℹ️ The :callback option specifies a callback that will be invoked each time the watched secret has been updated on disk. Default to a function with no effect.

   ℹ️ The :value option specifies the initial value of the secret (default to nil for in-memory secrets). Supersed the value from the file if the :directory option has been set.

   👉 You can add in-memory secrets dynamically with SecretAgent.put_secret/3.

• Configure and add secret_agent to your supervision tree:

  children =
    [
      {SecretAgent,
       [
         name: :secrets,
         secret_agent_config: [secrets: secrets]
       ]}
    ]
  
  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)

  ℹ️ If you don't specify the :name option, SecretAgent will be used by default.

  👉 By default, secret_agent trim watched secrets read on disk with String.trim/1. You can deactivate this behavior with the option trim_secrets set to false.

• Whenever you want to retrieve a secret, use SecretAgent.get_secret/2:

  {:ok, wrapped_credentials} = SecretAgent.get_secret(:secrets, "credentials")
  secret = wrapped_credentials.()

  👉 As a best practice, secret_agent erases secrets when accessing them. You can override this behavior with the option erase: false.

• You can manually update secrets with SecretAgent.put_secret/3 and SecretAgent.erase_secret/2.