A composer.json example with the Nextend Social Login Pro Addon repository.

composer.json

{
    "name": "acme/brilliant-wordpress-site",
    "description": "My brilliant WordPress site",
    "repositories":[
        {
            "type":"composer",
            "url":"https://wpackagist.org",
            "only": [
                "wpackagist-plugin/*",
                "wpackagist-theme/*"
            ]
        },
	{
            "type": "composer",
            "url": "https://api.nextendweb.com/v1/composer/",
            "only": [
                "nextendweb/*"
            ]
	}
    ],
    "require": {
        "aws/aws-sdk-php":"*",
        "wpackagist-plugin/akismet":"dev-trunk",
        "wpackagist-plugin/wordpress-seo":">=7.0.2",
        "wpackagist-theme/hueman":"*",
	"nextendweb/nextend-social-login-pro": "dev-master"
    },
    "autoload": {
        "psr-0": {
            "Acme": "src/"
        }
    },
    "extra": {
        "installer-paths": {
            "wp-content/mu-plugins/{$name}/": [
                "wpackagist-plugin/akismet"
            ],
            "wp-content/plugins/{$name}/": [
                "type:wordpress-plugin"
            ]
        }
    }
}