Elixir Certificate Import

The Erlang function :public_key.cacerts_load/1 can be used to load trusted CA certificates from a file, and with any Erlang function, it can be called from Elixir. The spec for this function shows it returns either :ok or a tuple of {:error, reason}:

-spec cacerts_load(File :: file:filename_all()) -> ok | {error, Reason :: term()}

Conveniently, the error format matches the failure state for the Application.start callback:

@callback start(start_type(), start_args :: term()) ::
  {:ok, pid()} | {:ok, pid(), state()} | {:error, reason :: term()}

Using the with keyword makes importing certificates at application start a breeze:

defmodule ApplicationStart do
    use Application

    @cacert_path Path.join(:code.priv_dir(:myapp), "cacert.pem")

    # {:error, reason} is returned if there is an issue loading CA Certs, which also matches
    # the return type of the Application `start` callback
    def start(_type, _args) do
        with :ok <- :public_key.cacerts_load(@cacert_path) do   # <-- Importing
            Supervisor.start_link([], strategy: :one_for_one)   # <-- Applications starts
        end
    end
end