Merge #3761

3761: added idna function to perform puny encoding on IDN domains (backport #3758) r=mergify[bot] a=mergify[bot]

## What type of PR?

bug-fix

## What does this PR do?

### Related issue(s)
- fixes issue where DKIM signatures from domains with IDN are not accepted by some mail servers: closes #3743

## Prerequisites
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.

- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/workflow.html#changelog) entry file.
<hr>This is an automatic backport of pull request #3758 done by [Mergify](https://mergify.com).

Co-authored-by: Jumper78 <52802286+Jumper78@users.noreply.github.com>
Co-authored-by: Florent Daigniere <nextgens@users.noreply.github.com>

core/admin/mailu/internal/views/rspamd.py

@@ -2,6 +2,7 @@ from mailu import models
 from mailu.internal import internal
 
 import flask
+import idna
 
 def vault_error(*messages, status=404):
     return flask.make_response(flask.jsonify({'errors':messages}), status)
@@ -19,7 +20,16 @@ def rspamd_dkim_key(domain_name):
         if key := domain.dkim_key:
             selectors.append(
                 {
-                    'domain'  : domain.name,
+                    'domain'  : idna.encode(domain.name.lower()).decode('ascii'),
+                    'key'     : key.decode('utf8'),
+                    'selector': flask.current_app.config.get('DKIM_SELECTOR', 'dkim'),
+                }
+            )
+    elif domain := models.Alternative.query.get(domain_name):
+        if key := domain.domain.dkim_key:
+            selectors.append(
+                {
+                    'domain'  : idna.encode(domain.name.lower()).decode('ascii'),
                     'key'     : key.decode('utf8'),
                     'selector': flask.current_app.config.get('DKIM_SELECTOR', 'dkim'),
                 }

towncrier/newsfragments/3758.bugfix

@@ -0,0 +1 @@
+domain name of an IDN domain in the DKIM signature needs to follow RFC6376; puny encoding the domain name when rspamd accesses the vault;