diff --git a/lib/pleroma/plugs/http_signature.ex b/lib/pleroma/plugs/http_signature.ex
index e2874c469..d87fa52fa 100644
--- a/lib/pleroma/plugs/http_signature.ex
+++ b/lib/pleroma/plugs/http_signature.ex
@@ -3,7 +3,6 @@
 # SPDX-License-Identifier: AGPL-3.0-only
 
 defmodule Pleroma.Web.Plugs.HTTPSignaturePlug do
-  alias Pleroma.Web.ActivityPub.Utils
   import Plug.Conn
   require Logger
 
@@ -16,38 +15,30 @@ defmodule Pleroma.Web.Plugs.HTTPSignaturePlug do
   end
 
   def call(conn, _opts) do
-    user = Utils.get_ap_id(conn.params["actor"])
-    Logger.debug("Checking sig for #{user}")
     [signature | _] = get_req_header(conn, "signature")
 
-    cond do
-      signature && String.contains?(signature, user) ->
-        # set (request-target) header to the appropriate value
-        # we also replace the digest header with the one we computed
-        conn =
-          conn
-          |> put_req_header(
-            "(request-target)",
-            String.downcase("#{conn.method}") <> " #{conn.request_path}"
-          )
-
-        conn =
-          if conn.assigns[:digest] do
-            conn
-            |> put_req_header("digest", conn.assigns[:digest])
-          else
-            conn
-          end
-
-        assign(conn, :valid_signature, HTTPSignatures.validate_conn(conn))
-
-      signature ->
-        Logger.debug("Signature not from actor")
-        assign(conn, :valid_signature, false)
-
-      true ->
-        Logger.debug("No signature header!")
+    if signature do
+      # set (request-target) header to the appropriate value
+      # we also replace the digest header with the one we computed
+      conn =
         conn
+        |> put_req_header(
+          "(request-target)",
+          String.downcase("#{conn.method}") <> " #{conn.request_path}"
+        )
+
+      conn =
+        if conn.assigns[:digest] do
+          conn
+          |> put_req_header("digest", conn.assigns[:digest])
+        else
+          conn
+        end
+
+      assign(conn, :valid_signature, HTTPSignatures.validate_conn(conn))
+    else
+      Logger.debug("No signature header!")
+      conn
     end
   end
 end
diff --git a/lib/pleroma/plugs/mapped_signature_to_identity_plug.ex b/lib/pleroma/plugs/mapped_signature_to_identity_plug.ex
new file mode 100644
index 000000000..ce8494b9d
--- /dev/null
+++ b/lib/pleroma/plugs/mapped_signature_to_identity_plug.ex
@@ -0,0 +1,70 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Plugs.MappedSignatureToIdentityPlug do
+  alias Pleroma.Signature
+  alias Pleroma.User
+  alias Pleroma.Web.ActivityPub.Utils
+
+  import Plug.Conn
+  require Logger
+
+  def init(options), do: options
+
+  defp key_id_from_conn(conn) do
+    with %{"keyId" => key_id} <- HTTPSignatures.signature_for_conn(conn) do
+      Signature.key_id_to_actor_id(key_id)
+    else
+      _ ->
+        nil
+    end
+  end
+
+  defp user_from_key_id(conn) do
+    with key_actor_id when is_binary(key_actor_id) <- key_id_from_conn(conn),
+         {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(key_actor_id) do
+      user
+    else
+      _ ->
+        nil
+    end
+  end
+
+  def call(%{assigns: %{user: _}} = conn, _opts), do: conn
+
+  # if this has payload make sure it is signed by the same actor that made it
+  def call(%{assigns: %{valid_signature: true}, params: %{"actor" => actor}} = conn, _opts) do
+    with actor_id <- Utils.get_ap_id(actor),
+         {:user, %User{} = user} <- {:user, user_from_key_id(conn)},
+         {:user_match, true} <- {:user_match, user.ap_id == actor_id} do
+      assign(conn, :user, user)
+    else
+      {:user_match, false} ->
+        Logger.debug("Failed to map identity from signature (payload actor mismatch)")
+        Logger.debug("key_id=#{key_id_from_conn(conn)}, actor=#{actor}")
+        assign(conn, :valid_signature, false)
+
+      # remove me once testsuite uses mapped capabilities instead of what we do now
+      {:user, nil} ->
+        Logger.debug("Failed to map identity from signature (lookup failure)")
+        Logger.debug("key_id=#{key_id_from_conn(conn)}, actor=#{actor}")
+        conn
+    end
+  end
+
+  # no payload, probably a signed fetch
+  def call(%{assigns: %{valid_signature: true}} = conn, _opts) do
+    with %User{} = user <- user_from_key_id(conn) do
+      assign(conn, :user, user)
+    else
+      _ ->
+        Logger.debug("Failed to map identity from signature (no payload actor mismatch)")
+        Logger.debug("key_id=#{key_id_from_conn(conn)}")
+        assign(conn, :valid_signature, false)
+    end
+  end
+
+  # no signature at all
+  def call(conn, _opts), do: conn
+end
diff --git a/lib/pleroma/signature.ex b/lib/pleroma/signature.ex
index a45c70a9d..2a0823ecf 100644
--- a/lib/pleroma/signature.ex
+++ b/lib/pleroma/signature.ex
@@ -9,7 +9,7 @@ defmodule Pleroma.Signature do
   alias Pleroma.User
   alias Pleroma.Web.ActivityPub.ActivityPub
 
-  defp key_id_to_actor_id(key_id) do
+  def key_id_to_actor_id(key_id) do
     URI.parse(key_id)
     |> Map.put(:fragment, nil)
     |> URI.to_string()
diff --git a/lib/pleroma/web/router.ex b/lib/pleroma/web/router.ex
index 8095ac4b1..518720d38 100644
--- a/lib/pleroma/web/router.ex
+++ b/lib/pleroma/web/router.ex
@@ -617,6 +617,7 @@ defmodule Pleroma.Web.Router do
   pipeline :activitypub do
     plug(:accepts, ["activity+json", "json"])
     plug(Pleroma.Web.Plugs.HTTPSignaturePlug)
+    plug(Pleroma.Web.Plugs.MappedSignatureToIdentityPlug)
   end
 
   scope "/", Pleroma.Web.ActivityPub do
diff --git a/mix.exs b/mix.exs
index e4ea19bb6..c12b0a500 100644
--- a/mix.exs
+++ b/mix.exs
@@ -138,7 +138,7 @@ defmodule Pleroma.Mixfile do
        ref: "95e8188490e97505c56636c1379ffdf036c1fdde"},
       {:http_signatures,
        git: "https://git.pleroma.social/pleroma/http_signatures.git",
-       ref: "a2a5982fa167fb1352fbd518ce6b606ba233a989"},
+       ref: "293d77bb6f4a67ac8bde1428735c3b42f22cbb30"},
       {:pleroma_job_queue, "~> 0.2.0"},
       {:telemetry, "~> 0.3"},
       {:prometheus_ex, "~> 3.0"},
diff --git a/mix.lock b/mix.lock
index 6477c1ed5..45142ba8f 100644
--- a/mix.lock
+++ b/mix.lock
@@ -38,7 +38,7 @@
   "hackney": {:hex, :hackney, "1.15.1", "9f8f471c844b8ce395f7b6d8398139e26ddca9ebc171a8b91342ee15a19963f4", [:rebar3], [{:certifi, "2.5.1", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "6.0.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "1.0.1", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~>1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "1.1.4", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}], "hexpm"},
   "html_entities": {:hex, :html_entities, "0.4.0", "f2fee876858cf6aaa9db608820a3209e45a087c5177332799592142b50e89a6b", [:mix], [], "hexpm"},
   "html_sanitize_ex": {:hex, :html_sanitize_ex, "1.3.0", "f005ad692b717691203f940c686208aa3d8ffd9dd4bb3699240096a51fa9564e", [:mix], [{:mochiweb, "~> 2.15", [hex: :mochiweb, repo: "hexpm", optional: false]}], "hexpm"},
-  "http_signatures": {:git, "https://git.pleroma.social/pleroma/http_signatures.git", "a2a5982fa167fb1352fbd518ce6b606ba233a989", [ref: "a2a5982fa167fb1352fbd518ce6b606ba233a989"]},
+  "http_signatures": {:git, "https://git.pleroma.social/pleroma/http_signatures.git", "293d77bb6f4a67ac8bde1428735c3b42f22cbb30", [ref: "293d77bb6f4a67ac8bde1428735c3b42f22cbb30"]},
   "httpoison": {:hex, :httpoison, "1.2.0", "2702ed3da5fd7a8130fc34b11965c8cfa21ade2f232c00b42d96d4967c39a3a3", [:mix], [{:hackney, "~> 1.8", [hex: :hackney, repo: "hexpm", optional: false]}], "hexpm"},
   "idna": {:hex, :idna, "6.0.0", "689c46cbcdf3524c44d5f3dde8001f364cd7608a99556d8fbd8239a5798d4c10", [:rebar3], [{:unicode_util_compat, "0.4.1", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm"},
   "jason": {:hex, :jason, "1.1.2", "b03dedea67a99223a2eaf9f1264ce37154564de899fd3d8b9a21b1a6fd64afe7", [:mix], [{:decimal, "~> 1.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm"},
diff --git a/test/plugs/http_signature_plug_test.exs b/test/plugs/http_signature_plug_test.exs
index efd811df7..d6fd9ea81 100644
--- a/test/plugs/http_signature_plug_test.exs
+++ b/test/plugs/http_signature_plug_test.exs
@@ -26,22 +26,4 @@ defmodule Pleroma.Web.Plugs.HTTPSignaturePlugTest do
       assert called(HTTPSignatures.validate_conn(:_))
     end
   end
-
-  test "bails out early if the signature isn't by the activity actor" do
-    params = %{"actor" => "https://mst3k.interlinked.me/users/luciferMysticus"}
-    conn = build_conn(:get, "/doesntmattter", params)
-
-    with_mock HTTPSignatures, validate_conn: fn _ -> false end do
-      conn =
-        conn
-        |> put_req_header(
-          "signature",
-          "keyId=\"http://mastodon.example.org/users/admin#main-key"
-        )
-        |> HTTPSignaturePlug.call(%{})
-
-      assert conn.assigns.valid_signature == false
-      refute called(HTTPSignatures.validate_conn(:_))
-    end
-  end
 end
diff --git a/test/plugs/mapped_identity_to_signature_plug_test.exs b/test/plugs/mapped_identity_to_signature_plug_test.exs
new file mode 100644
index 000000000..bb45d9edf
--- /dev/null
+++ b/test/plugs/mapped_identity_to_signature_plug_test.exs
@@ -0,0 +1,59 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2018 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Plugs.MappedSignatureToIdentityPlugTest do
+  use Pleroma.Web.ConnCase
+  alias Pleroma.Web.Plugs.MappedSignatureToIdentityPlug
+
+  import Tesla.Mock
+  import Plug.Conn
+
+  setup do
+    mock(fn env -> apply(HttpRequestMock, :request, [env]) end)
+    :ok
+  end
+
+  defp set_signature(conn, key_id) do
+    conn
+    |> put_req_header("signature", "keyId=\"#{key_id}\"")
+    |> assign(:valid_signature, true)
+  end
+
+  test "it successfully maps a valid identity with a valid signature" do
+    conn =
+      build_conn(:get, "/doesntmattter")
+      |> set_signature("http://mastodon.example.org/users/admin")
+      |> MappedSignatureToIdentityPlug.call(%{})
+
+    refute is_nil(conn.assigns.user)
+  end
+
+  test "it successfully maps a valid identity with a valid signature with payload" do
+    conn =
+      build_conn(:post, "/doesntmattter", %{"actor" => "http://mastodon.example.org/users/admin"})
+      |> set_signature("http://mastodon.example.org/users/admin")
+      |> MappedSignatureToIdentityPlug.call(%{})
+
+    refute is_nil(conn.assigns.user)
+  end
+
+  test "it considers a mapped identity to be invalid when it mismatches a payload" do
+    conn =
+      build_conn(:post, "/doesntmattter", %{"actor" => "http://mastodon.example.org/users/admin"})
+      |> set_signature("https://niu.moe/users/rye")
+      |> MappedSignatureToIdentityPlug.call(%{})
+
+    assert %{valid_signature: false} == conn.assigns
+  end
+
+  @tag skip: "known breakage; the testsuite presently depends on it"
+  test "it considers a mapped identity to be invalid when the identity cannot be found" do
+    conn =
+      build_conn(:post, "/doesntmattter", %{"actor" => "http://mastodon.example.org/users/admin"})
+      |> set_signature("http://niu.moe/users/rye")
+      |> MappedSignatureToIdentityPlug.call(%{})
+
+    assert %{valid_signature: false} == conn.assigns
+  end
+end