Instalación de extensiones de Magento2 desde gitHub

Quiero modificar una extensión del repository público de Github (fork) e instalarla en mi Magento2 vía composer .

Extensiones almacenadas aquí GitHub . Realmente, solo necesito una sample-external-links . Intenté muchas veces configurar composer.json en mi raíz de Magento2, pero no funciona, recibo errores:

[Composer \ Downloader \ TransportException] No se pudo download el file " https://api.github.com/repos/magento/magento2-samples/sample-external-links " (HTTP / 1.1 404 no encontrado)

¿Cómo configurar el compositor para instalar solo 1 package desde algún repository como ese?

mi compositor.json:

 { "name": "magento/project-community-edition", "description": "eCommerce Platform for Growth (Community Edition)", "type": "project", "version": "2.1.0", "license": [ "OSL-3.0", "AFL-3.0" ], "require": { "magento/product-community-edition": "2.1.0", "composer/composer": "@alpha", "magento/sample-bundle-all": "dev-master" }, "require-dev": { "phpunit/phpunit": "4.1.0", "squizlabs/php_codesniffer": "1.5.3", "phpmd/phpmd": "@stable", "pdepend/pdepend": "2.2.2", "fabpot/php-cs-fixer": "~1.2", "lusitanian/oauth": "~0.3 <=0.7.0", "sebastian/phpcpd": "2.0.0" }, "config": { "use-include-path": true }, "autoload": { "psr-4": { "Magento\\Framework\\": "lib/internal/Magento/Framework/", "Magento\\Setup\\": "setup/src/Magento/Setup/", "Magento\\": "app/code/Magento/" }, "psr-0": { "": "app/code/" }, "files": [ "app/etc/NonComposerComponentRegistration.php" ] }, "autoload-dev": { "psr-4": { "Magento\\Sniffs\\": "dev/tests/static/framework/Magento/Sniffs/", "Magento\\Tools\\": "dev/tools/Magento/Tools/", "Magento\\Tools\\Sanity\\": "dev/build/publication/sanity/Magento/Tools/Sanity/", "Magento\\TestFramework\\Inspection\\": "dev/tests/static/framework/Magento/TestFramework/Inspection/", "Magento\\TestFramework\\Utility\\": "dev/tests/static/framework/Magento/TestFramework/Utility/" } }, "minimum-stability": "alpha", "prefer-stable": true, "repositories": [ { "type": "vcs", "url": "https://github.com/magento/magento2-samples/sample-external-links" } ], "extra": { "magento-force": "override" }