title: Can’t access admin when WordPress is in a subfolder
body: <p>I installed WordPress using <a href="https://hub.docker.com/_/wordpress/" rel="nofollow noreferrer">this Docker image</a>. I installed WordPress in a sub-folder (<a href="https://thibault.vlacich.fr/blog" rel="nofollow noreferrer">https://thibault.vlacich.fr/blog</a>).</p>
  
  <p>I’m using Traefik for routing. Here’s my docker-compose file:</p>
  
  <pre><code>version: '3.7'
  
  networks:
    http_network:
      external: true
    thibaultvlacich:
      external: false
  
  services:
    database:
      image: mariadb:latest
      command: ['--character-set-server=utf8mb4', '--collation-server=utf8mb4_unicode_ci', '--default-authentication-plugin=mysql_native_password']
      volumes:
        - .docker/data/db:/var/lib/mysql
      environment:
        MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
        MYSQL_DATABASE: ${MYSQL_DATABASE}
        MYSQL_USER: ${MYSQL_USER}
        MYSQL_PASSWORD: ${MYSQL_PASSWORD}
      networks:
        - thibaultvlacich
  
    wordpress:
      depends_on:
        - database
      image: wordpress:latest
      volumes:
        - ./wordpress/wp-content:/var/www/html/wp-content
      environment:
        WORDPRESS_DB_HOST: database:3306
        WORDPRESS_DB_USER: ${MYSQL_USER}
        WORDPRESS_DB_PASSWORD: ${MYSQL_PASSWORD}
        WORDPRESS_DB_NAME: ${MYSQL_DATABASE}
      labels:
        - traefik.enable=true
        - traefik.frontend.rule=Host:thibault.vlacich.fr;PathPrefix:/blog;PathPrefixStrip:/blog
        - traefik.port=80
        - traefik.docker.network=http_network
      networks:
        - thibaultvlacich
        - http_network
  </code></pre>
  
  <p>Everything is working fine, at the exception of the admin. When I go to <a href="https://thibault.vlacich.fr/blog/wp-admin" rel="nofollow noreferrer">https://thibault.vlacich.fr/blog/wp-admin</a>, I’m redirected to <a href="https://thibault.vlacich.fr/wp-admin" rel="nofollow noreferrer">https://thibault.vlacich.fr/wp-admin</a>, and then can’t access the admin.</p>
  
  <p>Any idea how I could fix that? (Both WP_HOME and WP_SITEURL are correctly set to <a href="https://thibault.vlacich.fr/blog" rel="nofollow noreferrer">https://thibault.vlacich.fr/blog</a>)</p>