Make captcha (kocaptcha) stateless

Also rename seconds_retained to seconds_valid since that's how it is
now. Put it down from 180 to 20 seconds. The answer data is now
stored in an encrypted text transfered to the client and back, so no
ETS is needed

lib/pleroma/captcha/captcha.ex

@@ -1,8 +1,6 @@
 defmodule Pleroma.Captcha do
   use GenServer
 
-  @ets_options [:ordered_set, :private, :named_table, {:read_concurrency, true}]
-
   @doc false
   def start_link() do
     GenServer.start_link(__MODULE__, [], name: __MODULE__)
@@ -10,14 +8,6 @@ defmodule Pleroma.Captcha do
 
   @doc false
   def init(_) do
-    # Create a ETS table to store captchas
-    ets_name = Module.concat(method(), Ets)
-    ^ets_name = :ets.new(Module.concat(method(), Ets), @ets_options)
-
-    # Clean up old captchas every few minutes
-    seconds_retained = Pleroma.Config.get!([__MODULE__, :seconds_retained])
-    Process.send_after(self(), :cleanup, 1000 * seconds_retained)
-
     {:ok, nil}
   end
 
@@ -31,8 +21,8 @@ defmodule Pleroma.Captcha do
   @doc """
   Ask the configured captcha service to validate the captcha
   """
-  def validate(token, captcha) do
-    GenServer.call(__MODULE__, {:validate, token, captcha})
+  def validate(token, captcha, answer_data) do
+    GenServer.call(__MODULE__, {:validate, token, captcha, answer_data})
   end
 
   @doc false
@@ -47,19 +37,8 @@ defmodule Pleroma.Captcha do
   end
 
   @doc false
-  def handle_call({:validate, token, captcha}, _from, state) do
-    {:reply, method().validate(token, captcha), state}
-  end
-
-  @doc false
-  def handle_info(:cleanup, state) do
-    :ok = method().cleanup()
-
-    seconds_retained = Pleroma.Config.get!([__MODULE__, :seconds_retained])
-    # Schedule the next clenup
-    Process.send_after(self(), :cleanup, 1000 * seconds_retained)
-
-    {:noreply, state}
+  def handle_call({:validate, token, captcha, answer_data}, _from, state) do
+    {:reply, method().validate(token, captcha, answer_data), state}
   end
 
   defp method, do: Pleroma.Config.get!([__MODULE__, :method])