Merge #1968

1968: optimize handle_authentication r=mergify[bot] a=ghostwheel42

## What type of PR?

bug-fix

## What does this PR do?

catch utf-8 decoding errors and log a warning in handle_authentication instead of writing a traceback into the log.

### Related issue(s)

closes #1361

## Prerequistes

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] In case of feature or enhancement: documentation updated accordingly
- [X] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/workflow.html#changelog) entry file.


Co-authored-by: Alexander Graf <ghostwheel42@users.noreply.github.com>

core/admin/mailu/internal/nginx.py

@@ -71,16 +71,6 @@ def handle_authentication(headers):
             }
     # Authenticated user
     elif method == "plain":
-        server, port = get_server(headers["Auth-Protocol"], True)
-        # According to RFC2616 section 3.7.1 and PEP 3333, HTTP headers should
-        # be ASCII and are generally considered ISO8859-1. However when passing
-        # the password, nginx does not transcode the input UTF string, thus
-        # we need to manually decode.
-        raw_user_email = urllib.parse.unquote(headers["Auth-User"])
-        user_email = raw_user_email.encode("iso8859-1").decode("utf8")
-        raw_password = urllib.parse.unquote(headers["Auth-Pass"])
-        password = raw_password.encode("iso8859-1").decode("utf8")
-        ip = urllib.parse.unquote(headers["Client-Ip"])
         service_port = int(urllib.parse.unquote(headers["Auth-Port"]))
         if service_port == 25:
             return {
@@ -88,14 +78,27 @@ def handle_authentication(headers):
                 "Auth-Error-Code": "502 5.5.1",
                 "Auth-Wait": 0
             }
+        # According to RFC2616 section 3.7.1 and PEP 3333, HTTP headers should
+        # be ASCII and are generally considered ISO8859-1. However when passing
+        # the password, nginx does not transcode the input UTF string, thus
+        # we need to manually decode.
+        raw_user_email = urllib.parse.unquote(headers["Auth-User"])
+        raw_password = urllib.parse.unquote(headers["Auth-Pass"])
+        try:
+            user_email = raw_user_email.encode("iso8859-1").decode("utf8")
+            password = raw_password.encode("iso8859-1").decode("utf8")
+        except:
+            app.logger.warn(f'Received undecodable user/password from nginx: {raw_user_email!r}/{raw_password!r}')
+        else:
             user = models.User.query.get(user_email)
+            ip = urllib.parse.unquote(headers["Client-Ip"])
             if check_credentials(user, password, ip, protocol):
+                server, port = get_server(headers["Auth-Protocol"], True)
                 return {
                     "Auth-Status": "OK",
                     "Auth-Server": server,
                     "Auth-Port": port
                 }
-        else:
         status, code = get_status(protocol, "authentication")
         return {
             "Auth-Status": status,