1 files changed, 45 insertions, 8 deletions
diff --git a/lib/pleroma/web/plugs/http_signature_plug.ex b/lib/pleroma/web/plugs/http_signature_plug.ex
index d023754a6..4bf325218 100644
--- a/lib/pleroma/web/plugs/http_signature_plug.ex
+++ b/lib/pleroma/web/plugs/http_signature_plug.ex
@@ -25,21 +25,58 @@ defmodule Pleroma.Web.Plugs.HTTPSignaturePlug do
     end
   end
 
+  defp validate_signature(conn, request_target) do
+    # Newer drafts for HTTP signatures now use @request-target instead of the
+    # old (request-target). We'll now support both for incoming signatures.
+    conn =
+      conn
+      |> put_req_header("(request-target)", request_target)
+      |> put_req_header("@request-target", request_target)
+
+    HTTPSignatures.validate_conn(conn)
+  end
+
+  defp validate_signature(conn) do
+    # This (request-target) is non-standard, but many implementations do it
+    # this way due to a misinterpretation of
+    # https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-06
+    # "path" was interpreted as not having the query, though later examples
+    # show that it must be the absolute path + query. This behavior is kept to
+    # make sure most software (Pleroma itself, Mastodon, and probably others)
+    # do not break.
+    request_target = String.downcase("#{conn.method}") <> " #{conn.request_path}"
+
+    # This is the proper way to build the @request-target, as expected by
+    # many HTTP signature libraries, clarified in the following draft:
+    # https://www.ietf.org/archive/id/draft-ietf-httpbis-message-signatures-11.html#section-2.2.6
+    # It is the same as before, but containing the query part as well.
+    proper_target = request_target <> "?#{conn.query_string}"
+
+    cond do
+      # Normal, non-standard behavior but expected by Pleroma and more.
+      validate_signature(conn, request_target) ->
+        true
+
+      # Has query string and the previous one failed: let's try the standard.
+      conn.query_string != "" ->
+        validate_signature(conn, proper_target)
+
+      # If there's no query string and signature fails, it's rotten.
+      true ->
+        false
+    end
+  end
+
   defp maybe_assign_valid_signature(conn) do
     if has_signature_header?(conn) do
-      # set (request-target) header to the appropriate value
-      # we also replace the digest header with the one we computed
-      request_target = String.downcase("#{conn.method}") <> " #{conn.request_path}"
-
+      # we replace the digest header with the one we computed in DigestPlug
       conn =
-        conn
-        |> put_req_header("(request-target)", request_target)
-        |> case do
+        case conn do
           %{assigns: %{digest: digest}} = conn -> put_req_header(conn, "digest", digest)
           conn -> conn
         end
 
-      assign(conn, :valid_signature, HTTPSignatures.validate_conn(conn))
+      assign(conn, :valid_signature, validate_signature(conn))
     else
       Logger.debug("No signature header!")
       conn