Real Client-Ip with Cloudflare, Docker, Traefik and nginx set up as a mail proxy (Client-Ip in PHP script, not in upstream mail server)

I set nginx as a mail proxy, but i have trouble detecting the real Client-Ip in the php authentication script called by nginx via auth_http.
I am not interested in getting real-IP on the upstream mail server.

This is my stack:

• Cloudflare manages dns
• The rest is all handled with Docker

docker-compose.yml:

version: '3.9'

services:
  traefik:
    container_name: traefik
    image: traefik:v2.6.0
    ports:
      - "80:80"
      - "443:443"
      - "465:465"
      - "993:993"
      - "995:995"
      ...
    labels:
      - traefik.enable=true
      - traefik.http.routers.traefik-public-https.tls=true
      ...
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock:ro
      ...
    command:
      - --providers.docker
      - --providers.docker.exposedbydefault=false
      - --entrypoints.http.address=:80
      - --entrypoints.https.address=:443
      - --entrypoints.entrypoint-nginx-mail-465.address=:465
      - --entrypoints.entrypoint-nginx-mail-993.address=:993
      - --entrypoints.entrypoint-nginx-mail-995.address=:995
      - --entrypoints.entrypoint-forwardedHeaders-trustedIPs.forwardedHeaders.trustedIPs=${TRAEFIK_TRUSTED_IPS}
      ...

  nginx:
    container_name: nginx
    image: nginx:1.21
    volumes:
      - ${PWD}/sys/nginx/vhosts:/etc/nginx/conf.d
      - ${PWD}/sys/nginx/custom.d:/etc/nginx/custom.d
      ...
    labels:
      - traefik.enable=true

      - traefik.tcp.routers.router-nginx-mail-465.entrypoints=entrypoint-nginx-mail-465
      - traefik.tcp.routers.router-nginx-mail-465.rule=HostSNI(`*`)
      - traefik.tcp.routers.router-nginx-mail-465.tls=true
      - traefik.tcp.routers.router-nginx-mail-465.tls.certresolver=le
      - traefik.tcp.routers.router-nginx-mail-465.service=service-nginx-mail-465
      - traefik.tcp.services.service-nginx-mail-465.loadbalancer.server.port=587

      - traefik.tcp.routers.router-nginx-mail-993.entrypoints=entrypoint-nginx-mail-993
      - traefik.tcp.routers.router-nginx-mail-993.rule=HostSNI(`*`)
      - traefik.tcp.routers.router-nginx-mail-993.tls=true
      - traefik.tcp.routers.router-nginx-mail-993.tls.certresolver=le
      - traefik.tcp.routers.router-nginx-mail-993.service=service-nginx-mail-993
      - traefik.tcp.services.service-nginx-mail-993.loadbalancer.server.port=143

      - traefik.tcp.routers.router-nginx-mail-995.entrypoints=entrypoint-nginx-mail-995
      - traefik.tcp.routers.router-nginx-mail-995.rule=HostSNI(`*`)
      - traefik.tcp.routers.router-nginx-mail-995.tls=true
      - traefik.tcp.routers.router-nginx-mail-995.tls.certresolver=le
      - traefik.tcp.routers.router-nginx-mail-995.service=service-nginx-mail-995
      - traefik.tcp.services.service-nginx-mail-995.loadbalancer.server.port=110

      ...
  php-fpm:
    container_name: php-fpm
    image: bitnami/php-fpm:7.4
    userns_mode: 'host'
    labels:
      - traefik.enable=false
    ...

.env:

#https://www.cloudflare.com/ips
# Last updated: April 8, 2021
TRAEFIK_TRUSTED_IPS=173.245.48.0/20,103.21.244.0/22,103.22.200.0/22,103.31.4.0/22,141.101.64.0/18,108.162.192.0/18,190.93.240.0/20,188.114.96.0/20,197.234.240.0/22,198.41.128.0/17,162.158.0.0/15,104.16.0.0/13,104.24.0.0/14,172.64.0.0/13,131.0.72.0/22,2400:cb00::/32,2606:4700::/32,2803:f800::/32,2405:b500::/32,2405:8100::/32,2a06:98c0::/29,2c0f:f248::/32
...

sys/nginx/vhosts/00-main.conf:

server {
    listen [::]:80;
    listen 80;

    server_name localhost;

    root /app/public;

    index index.php;

    location ~ /\. {
        deny all;
    }

    location ~ \.php$ {
        fastcgi_pass php-fpm:9000;
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }
}

sys/nginx/custom.d/mail.conf:

mail {
    server_name _;
    auth_http localhost:80/proxy.php;
    proxy_pass_error_message on;

    imap_capabilities IMAP4 IMAP4rev1 LOGIN-REFERRALS SASL-IR ENABLE IDLE ID LITERAL+;
    pop3_capabilities CAPA RESP-CODES USER TOP AUTH-RESP-CODE PIPELINING UIDL;
    smtp_capabilities PIPELINING "SIZE ***" ETRN ENHANCEDSTATUSCODES 8BITMIME DSN CHUNKING;
    ...

    server {
        listen 110;
        protocol pop3;
        starttls on;
        auth_http_header X-Auth-Port 110;
        auth_http_header User-Agent "POP3 proxy";
    }

    server {
        listen 143;
        protocol imap;
        starttls on;
        auth_http_header X-Auth-Port 143;
        auth_http_header User-Agent "IMAP proxy";
    }

    server {
        listen 587;
        protocol smtp;
        starttls on;
        auth_http_header X-Auth-Port 587;
        auth_http_header User-Agent "SMTP proxy";
    }
}

getallheaders() inside proxy.php:

array (
  'User-Agent' => 'IMAP proxy',
  'X-Auth-Port' => '143',
  'Client-Ip' => '172.27.0.2',
  'Auth-Login-Attempt' => '1',
  'Auth-Protocol' => 'imap',
  'Auth-Pass' => '***',
  'Auth-User' => '***',
  'Auth-Method' => 'plain',
  'Host' => 'localhost',
  'Content-Length' => '',
  'Content-Type' => '',
)

$_SERVER inside proxy.php:

array (
  'HTTP_USER_AGENT' => 'IMAP proxy',
  'HTTP_X_AUTH_PORT' => '143',
  'HTTP_CLIENT_IP' => '172.27.0.2',
  'HTTP_AUTH_LOGIN_ATTEMPT' => '1',
  'HTTP_AUTH_PROTOCOL' => 'imap',
  'HTTP_AUTH_PASS' => '***',
  'HTTP_AUTH_USER' => '***',
  'HTTP_AUTH_METHOD' => 'plain',
  'HTTP_HOST' => 'localhost',
  'REDIRECT_STATUS' => '200',
  'SERVER_NAME' => 'localhost',
  'SERVER_PORT' => '80',
  'SERVER_ADDR' => '127.0.0.1',
  'REMOTE_PORT' => '49360',
  'REMOTE_ADDR' => '127.0.0.1',
  'SERVER_SOFTWARE' => 'nginx/1.21.3',
  'GATEWAY_INTERFACE' => 'CGI/1.1',
  'REQUEST_SCHEME' => 'http',
  'SERVER_PROTOCOL' => 'HTTP/1.0',
  'DOCUMENT_URI' => '/proxy.php',
  'REQUEST_URI' => '/',
  'SCRIPT_NAME' => '/proxy.php',
  'CONTENT_LENGTH' => '',
  'CONTENT_TYPE' => '',
  'REQUEST_METHOD' => 'GET',
  'QUERY_STRING' => '',
  'FCGI_ROLE' => 'RESPONDER',
  'PHP_SELF' => '/proxy.php',
  ...
)