Example composer.json

{
    "license": "proprietary",
    "type": "project",
    "repositories": {
        "drupal": {
            "type": "composer",
            "url": "https://packages.drupal.org/8"
        }
    },
    "require": {
        "drupal/core": "^8.0",
        "drupal/csv_serialization": "^1.0",
        "cweagans/composer-patches": "^1.6.0"
    },
    "require-dev": {},
    "extra": {
        "installer-paths": {
            "docroot/core": ["type:drupal-core"],
            "docroot/modules/contrib/{$name}": ["type:drupal-module"],
            "docroot/modules/custom/{$name}": ["type:drupal-custom-module"],
            "docroot/profiles/contrib/{$name}": ["type:drupal-profile"],
            "docroot/profiles/custom/{$name}": ["type:drupal-custom-profile"],
            "docroot/themes/contrib/{$name}": ["type:drupal-theme"],
            "docroot/themes/custom/{$name}": ["type:drupal-custom-theme"],
            "docroot/libraries/{$name}": ["type:drupal-library"],
            "drush/contrib/{$name}": ["type:drupal-drush"]
        },
        "drupal-scaffold": {
            "initial": {
                "sites/default/default.services.yml": "sites/default/services.yml",
                "sites/default/default.settings.php": "sites/default/settings.php"
             }
        },
        "enable-patching": true,
        "composer-exit-on-patch-failure": true,
        "patches": {
        }
    },
    "minimum-stability": "dev",
    "prefer-stable": true
}