Cannot make composer install work offline

I am trying to set up Composer to work without internet access. I have set up a server in the local network with a Satis configured repository with the following configuration file:

{
  "name": "private/composer",
  "homepage": "http://<some_ip>:9500",
  "repositories": [
    {"type": "composer", "url": "https://packagist.org"}
  ],
  "require-dependencies": true,
  "require": { ... },
  "archive": {
    "directory": "offline",
    "format": "zip"
  },
  "config": {
    "preferred-install": "dist"
  }
}

After running

$ ./satis/bin/satis build ./satis.json ./mirror

Everything works, I get my ./satis/mirror/offline directory filled up with .zip files of the packages I am mirroring from packagist.org.

In my Composer, project, I added the following sections to the composer.json configuration:

{
    "repositories": [{
        "type": "composer",
        "url": "http://<some_ip>:9500"
    }],
    "config": {
        "secure-http": false
    },
    ...
}

I tried to run composer install then and I get an error about Composer not begin able to access https://packagist.org/packages.json. Why is it trying to do that? How can I make this process work without internet access?

Thank you!

By default Composer does not disable access to packagist.org when you add custom repos. You can disable it with the following config:

{
    "repositories": [
        {
            "packagist.org": false
        }
    ]
}