Merge #2265

2265: Prevent an exception from being thrown if the username isn't an email address r=mergify[bot] a=nextgens

## What type of PR?

enhancement

## What does this PR do?

Mailu expects users to identify using an email address; some brute-force script don't send just an username and this leads to an exception... that makes the error message and return code vary.

This PR prevents the exceptions from being thrown in the first place

```
WARNING in nginx: Invalid user 'xxxx': (builtins.ValueError) invalid email address (no "`@")"`
```

### Related issue(s)
- closes #2261
- closes #1750

Co-authored-by: Florent Daigniere <nextgens@freenetproject.org>
Co-authored-by: Florent Daigniere <nextgens@users.noreply.github.com>

core/admin/mailu/internal/nginx.py

@@ -93,8 +93,8 @@ def handle_authentication(headers):
             app.logger.warn(f'Received undecodable user/password from nginx: {raw_user_email!r}/{raw_password!r}')
         else:
             try:
-                user = models.User.query.get(user_email)
-                is_valid_user = True
+                user = models.User.query.get(user_email) if '@' in user_email else None
+                is_valid_user = user is not None
             except sqlalchemy.exc.StatementError as exc:
                 exc = str(exc).split('\n', 1)[0]
                 app.logger.warn(f'Invalid user {user_email!r}: {exc}')

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

@@ -12,7 +12,7 @@ def nginx_authentication():
     """
     client_ip = flask.request.headers["Client-Ip"]
     headers = flask.request.headers
-    if headers["Auth-Port"] == '25' and headers['Auth-Method'] == 'plain':
+    if headers["Auth-Port"] == '25':
         response = flask.Response()
         response.headers['Auth-Status'] = 'AUTH not supported'
         response.headers['Auth-Error-Code'] = '502 5.5.1'

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

@@ -5,6 +5,7 @@ from flask import current_app as app
 import flask
 import idna
 import re
+import sqlalchemy.exc
 import srslib
 
 @internal.route("/postfix/dane/<domain_name>")
@@ -158,18 +159,13 @@ def postfix_sender_rate(sender):
 def postfix_sender_access(sender):
     """ Simply reject any sender that pretends to be from a local domain
     """
-    if not is_void_address(sender):
-        localpart, domain_name = models.Email.resolve_domain(sender)
-        return flask.jsonify("REJECT") if models.Domain.query.get(domain_name) else flask.abort(404)
-    else:
-        return flask.abort(404)
-
-
-def is_void_address(email):
-    '''True if the email is void (null) email address.
-    '''
-    if email.startswith('<') and email.endswith('>'):
-        email = email[1:-1]
-    # Some MTAs use things like '<MAILER-DAEMON>' instead of '<>'; so let's
-    # consider void any such thing.
-    return '@' not in email
+    if '@' in sender:
+        if sender.startswith('<') and sender.endswith('>'):
+            sender = sender[1:-1]
+        try:
+            localpart, domain_name = models.Email.resolve_domain(sender)
+            if models.Domain.query.get(domain_name):
+                return flask.jsonify("REJECT")
+        except sqlalchemy.exc.StatementError:
+            pass
+    return flask.abort(404)