Is it possible to disable account creation?

I just do any config with environment variables in the docker-compose. I assemble my docker-compose with ansible so here’s the vikunja backend (API) part from my jinja2 template (hence the curly braced variables):

vikunja-backend:
    container_name: 'vikunja-backend'
    image: vikunja/api
    environment:
      VIKUNJA_DATABASE_HOST: 'vikunja-db'
      VIKUNJA_DATABASE_PASSWORD: "{{ vikunja_db_password }}"
      VIKUNJA_DATABASE_TYPE: 'mysql'
      VIKUNJA_DATABASE_USER: 'vikunja'
      VIKUNJA_DATABASE_DATABASE: 'vikunja'
      VIKUNJA_REDIS_ENABLED: 1
      VIKUNJA_REDIS_HOST: 'vikunja-redis:6379'
      VIKUNJA_CACHE_ENABLED: 1
      VIKUNJA_CACHE_TYPE: redis
      VIKUNJA_SERVICE_FRONTENDURL: "https://vikunja.{{ traefik_domain }}"
      VIKUNJA_SERVICE_ENABLEREGISTRATION: 0
      VIKUNJA_MIGRATION_WUNDERLIST_ENABLE: 0
      VIKUNJA_MIGRATION_TODOIST_ENABLE: 1
      VIKUNJA_FILES_BASEPATH: "/app/vikunja/files"
      VIKUNJA_MAILER_ENABLED: 1
      VIKUNJA_MAILER_HOST: "{{ fqdn }}"
      VIKUNJA_MAILER_PORT: 587
      VIKUNJA_MAILER_USERNAME: 'vikunja'
      VIKUNJA_MAILER_PASSWORD: "{{ vikunja_email_password }}"
      VIKUNJA_MAILER_FROMEMAIL: "vikunja@{{ fqdn }}"
      VIKUNJA_MAILER_SKIPTLSVERIFY: 'true'
      PUID: "{{ docker_user_uid }}"
      PGID: "{{ docker_user_gid }}"
    volumes:
      - source: "{{ docker_data_dir }}/vikunja-backend"
        target: '/app/vikunja/files'
        type: 'bind'
    depends_on:
      - vikunja-db
      - vikunja-redis
    restart: "{{ restart_policy }}"
    labels:
      traefik.enable: 'true'
      traefik.http.routers.vikunja-backend.rule: "Host(`vikunja.{{ traefik_domain }}`) && PathPrefix(`/api/v1`, `/dav/`)"
      traefik.http.routers.vikunja-backend.tls: 'true'
      #traefik.http.routers.vikunja-backend.middlewares: 'access-whitelist@file'
      com.centurylinklabs.watchtower.enable: 'true'
    networks:
      - 'default'
      - 'frontend'

Obviously the formatting will may need tweaked to use directly in a docker-compose.yml file.