signature: properly deduce the actor from misskey key IDs

lib/pleroma/signature.ex

@@ -10,9 +10,18 @@ defmodule Pleroma.Signature do
   alias Pleroma.Web.ActivityPub.ActivityPub
 
   def key_id_to_actor_id(key_id) do
+    uri =
       URI.parse(key_id)
       |> Map.put(:fragment, nil)
-    |> URI.to_string()
+
+    uri =
+      if String.ends_with?(uri.path, "/publickey") do
+        Map.put(uri, :path, String.replace(uri.path, "/publickey", ""))
+      else
+        uri
+      end
+
+    URI.to_string(uri)
   end
 
   def fetch_public_key(conn) do

test/signature_test.exs

@@ -48,16 +48,14 @@ defmodule Pleroma.SignatureTest do
 
     test "it returns error when not found user" do
       assert capture_log(fn ->
-               assert Signature.fetch_public_key(make_fake_conn("test-ap_id")) ==
-                        {:error, :error}
+               assert Signature.fetch_public_key(make_fake_conn("test-ap_id")) == {:error, :error}
              end) =~ "[error] Could not decode user"
     end
 
     test "it returns error if public key is empty" do
       user = insert(:user, %{info: %{source_data: %{"publicKey" => %{}}}})
 
-      assert Signature.fetch_public_key(make_fake_conn(user.ap_id)) ==
-               {:error, :error}
+      assert Signature.fetch_public_key(make_fake_conn(user.ap_id)) == {:error, :error}
     end
   end
 
@@ -65,8 +63,7 @@ defmodule Pleroma.SignatureTest do
     test "it returns key" do
       ap_id = "https://mastodon.social/users/lambadalambda"
 
-      assert Signature.refetch_public_key(make_fake_conn(ap_id)) ==
-               {:ok, @rsa_public_key}
+      assert Signature.refetch_public_key(make_fake_conn(ap_id)) == {:ok, @rsa_public_key}
     end
 
     test "it returns error when not found user" do
@@ -105,4 +102,16 @@ defmodule Pleroma.SignatureTest do
              ) == {:error, []}
     end
   end
+
+  describe "key_id_to_actor_id/1" do
+    test "it properly deduces the actor id for misskey" do
+      assert Signature.key_id_to_actor_id("https://example.com/users/1234/publickey") ==
+               "https://example.com/users/1234"
+    end
+
+    test "it properly deduces the actor id for mastodon and pleroma" do
+      assert Signature.key_id_to_actor_id("https://example.com/users/1234#main-key") ==
+               "https://example.com/users/1234"
+    end
+  end
 end