Add also_known_as field to Pleroma.User

test/fixtures/tesla_mock/admin@mastdon.example.org.json

@@ -9,7 +9,11 @@
     "inReplyToAtomUri": "ostatus:inReplyToAtomUri",
     "conversation": "ostatus:conversation",
     "toot": "http://joinmastodon.org/ns#",
-    "Emoji": "toot:Emoji"
+    "Emoji": "toot:Emoji",
+    "alsoKnownAs": {
+      "@id": "as:alsoKnownAs",
+      "@type": "@id"
+    }
   }],
   "id": "http://mastodon.example.org/users/admin",
   "type": "Person",
@@ -50,5 +54,6 @@
     "type": "Image",
     "mediaType": "image/png",
     "url": "https://cdn.niu.moe/accounts/headers/000/033/323/original/850b3448fa5fd477.png"
-  }
+  },
+  "alsoKnownAs": ["http://example.org/users/foo"]
 }

test/web/activity_pub/transmogrifier_test.exs

@@ -592,6 +592,37 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       assert user.bio == "<p>Some bio</p>"
     end
 
+    test "it works with alsoKnownAs" do
+      {:ok, %Activity{data: %{"actor" => actor}}} =
+        "test/fixtures/mastodon-post-activity.json"
+        |> File.read!()
+        |> Poison.decode!()
+        |> Transmogrifier.handle_incoming()
+
+      assert User.get_cached_by_ap_id(actor).also_known_as == ["http://example.org/users/foo"]
+
+      {:ok, _activity} =
+        "test/fixtures/mastodon-update.json"
+        |> File.read!()
+        |> Poison.decode!()
+        |> Map.put("actor", actor)
+        |> Map.update!("object", fn object ->
+          object
+          |> Map.put("actor", actor)
+          |> Map.put("id", actor)
+          |> Map.put("alsoKnownAs", [
+            "http://mastodon.example.org/users/foo",
+            "http://example.org/users/bar"
+          ])
+        end)
+        |> Transmogrifier.handle_incoming()
+
+      assert User.get_cached_by_ap_id(actor).also_known_as == [
+               "http://mastodon.example.org/users/foo",
+               "http://example.org/users/bar"
+             ]
+    end
+
     test "it works with custom profile fields" do
       {:ok, activity} =
         "test/fixtures/mastodon-post-activity.json"