Bad gateway on configured Proxied app

[javierspn]

Describe the bug
I have the following setup:

1. Nginx proxy manager
2. Authentik server in the same docker network (default ports 9000 and 9443)
3. Nginx exposes the authentik container as a proxy host with http://authentik:9000 internally and as https://auth.example.com with a valid letsencrypt certificate.
4. An app and provider wiyh the following configuration (the app is anothr container in the same docker network with no authentication, it is a very simple web app called it-tools):

• App: Name: ittools / slug: ittools / provider: ittools
• Provider: Name: ittools / Authorization flow: default-provider-authorization-implicit-consent (Authorize Application) / External host: https://ittools.example.com/
• Outpost: default local docker connection

This is my docker configuration:

services:

  authentikpostgres:

    container_name: "${POSTGRES_CONTAINER_NAME}"
    image: ${POSTGRES_CONTAINER_IMAGE}

    environment:
      TZ: ${TZ}
      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
      POSTGRES_USER: ${POSTGRES_USER}
      POSTGRES_DB: ${POSTGRES_DB}

    networks:
      - proxied

    restart: ${POLICY_RESTART}

    healthcheck:
      test: ["CMD-SHELL", "pg_isready -d $${POSTGRES_DB} -U $${POSTGRES_USER}"]
      start_period: 20s
      interval: 30s
      retries: 5
      timeout: 5s

    volumes:
      - ${POSTGRES_CONTAINER_VOLUME}

    logging:

      driver: ${LOG_TYPE}
      options:
        max-size: ${LOG_SIZE}
        max-file: ${LOG_FILES}

  authentikredis:

    container_name: "${REDIS_CONTAINER_NAME}"
    image: ${REDIS_CONTAINER_IMAGE}

    command: --save 60 1 --loglevel warning

    environment:
      TZ: ${TZ}

    networks:
      - proxied

    restart: ${POLICY_RESTART}

    healthcheck:
      test: ["CMD-SHELL", "redis-cli ping | grep PONG"]
      start_period: 20s
      interval: 30s
      retries: 5
      timeout: 3s

    volumes:
      - ${REDIS_CONTAINER_VOLUME}

    logging:

      driver: ${LOG_TYPE}
      options:
        max-size: ${LOG_SIZE}
        max-file: ${LOG_FILES}

  authentikserver:

    container_name: "${AUTHENTIK_CONTAINER_NAME}"
    image: ${AUTHENTIK_CONTAINER_IMAGE}

    command: server

    environment:
      TZ: ${TZ}
      AUTHENTIK_REDIS__HOST: ${REDIS_CONTAINER_NAME}
      AUTHENTIK_POSTGRESQL__HOST: ${POSTGRES_CONTAINER_NAME}
      AUTHENTIK_POSTGRESQL__USER: ${POSTGRES_USER}
      AUTHENTIK_POSTGRESQL__NAME: ${POSTGRES_DB}
      AUTHENTIK_POSTGRESQL__PASSWORD: ${POSTGRES_PASSWORD}
      AUTHENTIK_SECRET_KEY: ${AUTHENTIK_SECRET_KEY}

    networks:
      - proxied

    restart: ${POLICY_RESTART}

    volumes:
      - ${AUTHENTIK_SERVER_MEDIA_VOLUME}
      - ${AUTHENTIK_SERVER_TEMPLATES_VOLUME}

    depends_on:
      authentikpostgres:
        condition: service_healthy
      authentikredis:
        condition: service_healthy

    logging:

      driver: ${LOG_TYPE}
      options:
        max-size: ${LOG_SIZE}
        max-file: ${LOG_FILES}

  authentikworker:

    container_name: "${AUTHENTIK_WORKER_CONTAINER_NAME}"
    image: ${AUTHENTIK_CONTAINER_IMAGE}

    command: worker

    user: root

    environment:
      TZ: ${TZ}
      AUTHENTIK_REDIS__HOST: ${REDIS_CONTAINER_NAME}
      AUTHENTIK_POSTGRESQL__HOST: ${POSTGRES_CONTAINER_NAME}
      AUTHENTIK_POSTGRESQL__USER: ${POSTGRES_USER}
      AUTHENTIK_POSTGRESQL__NAME: ${POSTGRES_DB}
      AUTHENTIK_POSTGRESQL__PASSWORD: ${POSTGRES_PASSWORD}
      AUTHENTIK_SECRET_KEY: ${AUTHENTIK_SECRET_KEY}

    networks:
      - proxied

    restart: ${POLICY_RESTART}

    volumes:
      - ${AUTHENTIK_DOCKER_SOCK_VOLUME}
      - ${AUTHENTIK_SERVER_MEDIA_VOLUME}
      - ${AUTHENTIK_WORKER_CERTS_VOLUME}
      - ${AUTHENTIK_SERVER_TEMPLATES_VOLUME}

    depends_on:
      authentikpostgres:
        condition: service_healthy
      authentikredis:
        condition: service_healthy

    logging:

      driver: ${LOG_TYPE}
      options:
        max-size: ${LOG_SIZE}
        max-file: ${LOG_FILES}

volumes:
  database:
    driver: local
  redis:
    driver: local

networks:
  proxied:
    name: proxied

I have exposed both ports for authentikserver too in the compose file to try it out:

    ports:
    - ${AUTHENTIK_PORT_HTTP} (9000)
    - ${AUTHENTIK_PORT_HTTPS} (9443)

The best I got was for the app to redirect on the public web to authentikserver:9000 as the outpost (which obviously fails).

this is the configuration of nginx proxy manager:

And this is the advanced config, the only change is the actual supposedly working outpost:

# Increase buffer size for large headers
# This is needed only if you get 'upstream sent too big header while reading response
# header from upstream' error when trying to access an application protected by goauthentik
proxy_buffers 8 16k;
proxy_buffer_size 32k;

# Make sure not to redirect traffic to a port 4443
port_in_redirect off;

location / {
    # Put your proxy_pass to your application here
    proxy_pass          $forward_scheme://$server:$port;
    # Set any other headers your application might need
    # proxy_set_header Host $host;
    # proxy_set_header ...

    ##############################
    # authentik-specific config
    ##############################
    auth_request     /outpost.goauthentik.io/auth/nginx;
    error_page       401 = @goauthentik_proxy_signin;
    auth_request_set $auth_cookie $upstream_http_set_cookie;
    add_header       Set-Cookie $auth_cookie;

    # translate headers from the outposts back to the actual upstream
    auth_request_set $authentik_username $upstream_http_x_authentik_username;
    auth_request_set $authentik_groups $upstream_http_x_authentik_groups;
    auth_request_set $authentik_entitlements $upstream_http_x_authentik_entitlements;
    auth_request_set $authentik_email $upstream_http_x_authentik_email;
    auth_request_set $authentik_name $upstream_http_x_authentik_name;
    auth_request_set $authentik_uid $upstream_http_x_authentik_uid;

    proxy_set_header X-authentik-username $authentik_username;
    proxy_set_header X-authentik-groups $authentik_groups;
    proxy_set_header X-authentik-entitlements $authentik_entitlements;
    proxy_set_header X-authentik-email $authentik_email;
    proxy_set_header X-authentik-name $authentik_name;
    proxy_set_header X-authentik-uid $authentik_uid;

    # This section should be uncommented when the "Send HTTP Basic authentication" option
    # is enabled in the proxy provider
    # auth_request_set $authentik_auth $upstream_http_authorization;
    # proxy_set_header Authorization $authentik_auth;
}

# all requests to /outpost.goauthentik.io must be accessible without authentication
location /outpost.goauthentik.io {
    # When using the embedded outpost, use:
    proxy_pass              https://auth.xxxx.com/outpost.goauthentik.io;
    # For manual outpost deployments:
    # proxy_pass              http://outpost.company:9000;

    # Note: ensure the Host header matches your external authentik URL:
    proxy_set_header        Host $host;

    proxy_set_header        X-Original-URL $scheme://$http_host$request_uri;
    add_header              Set-Cookie $auth_cookie;
    auth_request_set        $auth_cookie $upstream_http_set_cookie;
    proxy_pass_request_body off;
    proxy_set_header        Content-Length "";
}

# Special location for when the /auth endpoint returns a 401,
# redirect to the /start URL which initiates SSO
location @goauthentik_proxy_signin {
    internal;
    add_header Set-Cookie $auth_cookie;
    return 302 /outpost.goauthentik.io/start?rd=$request_uri;
    # For domain level, use the below error_page to redirect to your authentik server with the full redirect path
    # return 302 https://authentik.company/outpost.goauthentik.io/start?rd=$scheme://$http_host$request_uri;
}

Screenshots
Nginx proxy manager authentik:

There is a valid letsencrypt certificate.

Whenever I connect to the app, 500 Internal Server error is displayed.
To Reproduce
As above.

Expected behavior
To work XD

Logs
Output of docker-compose logs or kubectl logs respectively

Version and Deployment (please complete the following information):

• authentik version: 2024.12.3
• Deployment: docker-compose

Additional context
Add any other context about the problem here.