Stuck in composer

[suntong]

remove exec and shell_exec in php.ini

it's work to me.

[caedmon4wd809b]

Create a auth.json file on root of your project with following code:

{
    "http-basic": {
        "repo.magento.com": {
            "username":"<public-key>",
            "password":  "<private-key>"
        }
    }
}

Replace your public and private keys in double quotes without arrow signs. That should work.