Add plug to validate signed http requests.

lib/pleroma/web/http_signatures/http_signatures.ex

@@ -1,5 +1,7 @@
 # https://tools.ietf.org/html/draft-cavage-http-signatures-08
 defmodule Pleroma.Web.HTTPSignatures do
+  alias Pleroma.User
+
   def split_signature(sig) do
     default = %{"headers" => "date"}
 
@@ -18,7 +20,18 @@ defmodule Pleroma.Web.HTTPSignatures do
   def validate(headers, signature, public_key) do
     sigstring = build_signing_string(headers, signature["headers"])
     {:ok, sig} = Base.decode64(signature["signature"])
-    verify = :public_key.verify(sigstring, :sha256, sig, public_key)
+    :public_key.verify(sigstring, :sha256, sig, public_key)
+  end
+
+  def validate_conn(conn) do
+    # TODO: How to get the right key and see if it is actually valid for that request.
+    # For now, fetch the key for the actor.
+    with actor_id <- conn.params["actor"],
+         {:ok, public_key} <- User.get_public_key_for_ap_id(actor_id) do
+      validate_conn(conn, public_key)
+    else
+      _ -> false
+    end
   end
 
   def validate_conn(conn, public_key) do