2542: Implement header authentication via external proxy r=mergify[bot] a=nextgens
## What type of PR?
Feature
## What does this PR do?
Implement header authentication via external proxy
### Related issue(s)
- closes#1972
- closes#2183
## 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] 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.
2559: Turns out that php81-ctype is required by roundcube r=mergify[bot] a=nextgens
## What type of PR?
bug-fix
## What does this PR do?
It solves:
```
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "NOTICE: PHP message: PHP Fatal error: Uncaught Error: Call to undefined function Masterminds\HTML5\Parser\ctype_alpha() in /var/www/roundcube/vendor/masterminds/html5/src/HTML5/Parser/Tokenizer.php:140"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "Stack trace:"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "#0 /var/www/roundcube/vendor/masterminds/html5/src/HTML5/Parser/Tokenizer.php(82): Masterminds\HTML5\Parser\Tokenizer->consumeData()"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "#1 /var/www/roundcube/vendor/masterminds/html5/src/HTML5.php(161): Masterminds\HTML5\Parser\Tokenizer->parse()"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "#2 /var/www/roundcube/vendor/masterminds/html5/src/HTML5.php(89): Masterminds\HTML5->parse('<html>\n <hea...', Array)"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "#3 /var/www/roundcube/program/lib/Roundcube/rcube_washtml.php(700): Masterminds\HTML5->loadHTML('<html>\n <hea...')"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "#4 /var/www/roundcube/program/actions/mail/index.php(975): rcube_washtml->wash('<html>\n <hea...')"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "#5 /var/www/roundcube/program/actions/mail/index.php(1019): rcmail_action_mail_index::wash_html('<!doctype html>...', Array, Array)"
[25-Nov-2022 08:19:20] WARNING: [pool php] child 335 said into stderr: "#6 /var/www/roundcube/program/actions/mail/show.php(720): rcmail_action_mail_index::pr..."
```
see https://github.com/roundcube/roundcubemail/issues/7049
Co-authored-by: Florent Daigniere <nextgens@freenetproject.org>
Florent Daigniere