clacks/lib/clacks_web/plug/digest.ex

defmodule ClacksWeb.Plug.Digest do
  alias Plug.Conn

  def read_body(conn, opts) do
    {:ok, body, conn} = Conn.read_body(conn, opts)
    digest = "SHA-256=" <> Base.encode64(:crypto.hash(:sha256, body))
    {:ok, body, Conn.assign(conn, :digest, digest)}
  end
end