Add a task to generate web_push key pairs

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mix/tasks/mobilizon/web_push.ex

@@ -0,0 +1,32 @@
+defmodule Mix.Tasks.Mobilizon.WebPush.Gen.Keypair do
+  @moduledoc """
+  Task to generate WebPush configuration
+
+  Taken from https://github.com/danhper/elixir-web-push-encryption/blob/8fd0f71f3222b466d389f559be9800c49f9bb641/lib/mix/tasks/web_push_gen_keypair.ex
+  """
+  use Mix.Task
+  import Mix.Tasks.Mobilizon.Common, only: [mix_shell?: 0]
+
+  @shortdoc "Manages Mobilizon users"
+
+  @impl Mix.Task
+  def run(_) do
+    {public, private} = :crypto.generate_key(:ecdh, :prime256v1)
+
+    IO.puts("# Put the following in your #{file_name()} config file:")
+    IO.puts("")
+    IO.puts("config :web_push_encryption, :vapid_details,")
+    IO.puts("  subject: \"mailto:administrator@example.com\",")
+    IO.puts("  public_key: \"#{ub64(public)}\",")
+    IO.puts("  private_key: \"#{ub64(private)}\"")
+    IO.puts("")
+  end
+
+  defp ub64(value) do
+    Base.url_encode64(value, padding: false)
+  end
+
+  defp file_name do
+    if mix_shell?(), do: "runtime.exs", else: "config.exs"
+  end
+end