activitypub: switch to using x509 representation for public keys instead of pkcs#1

lib/pleroma/web/activity_pub/views/user_view.ex

@@ -12,7 +12,7 @@ defmodule Pleroma.Web.ActivityPub.UserView do
   def render("user.json", %{user: user}) do
     {:ok, user} = WebFinger.ensure_keys_present(user)
     {:ok, _, public_key} = Salmon.keys_from_pem(user.info["keys"])
-    public_key = :public_key.pem_entry_encode(:RSAPublicKey, public_key)
+    public_key = :public_key.pem_entry_encode(:SubjectPublicKeyInfo, public_key)
     public_key = :public_key.pem_encode([public_key])
 
     %{

test/web/activity_pub/views/user_view_test.exs

@@ -13,6 +13,6 @@ test "Renders a user, including the public key" do
     assert result["id"] == user.ap_id
     assert result["preferredUsername"] == user.nickname
 
-    assert String.contains?(result["publicKey"]["publicKeyPem"], "BEGIN RSA PUBLIC KEY")
+    assert String.contains?(result["publicKey"]["publicKeyPem"], "BEGIN PUBLIC KEY")
   end
 end