Cannot use GitLab private token for authorization

According to [documentation about using token in headers](https://getcomposer.org/doc/articles/handling-private-packages-with-satis.md) I cannot use my token.

Please take a look my issue https://github.com/composer/composer/pull/3765#issuecomment-245612489

my configuration doesn't work:

``` json
{
"name": "MySatis",
"homepage": "http://satis.example.com/",
"repositories": [
{
"url": "https://git.example.com/foo/bar.git",
"type": "gitlab",
"options": {
"http": {
"header": [
"PRIVATE-TOKEN: QWEQWEQWEQWE"
]
}
}
}
],
"require-all": true,
"output-dir": "html"
}
```

The options wasn't passed to the code.

Start with the linked private-package documentation and trace how the repository's options, especially the http header configuration, are passed into the GitLab request path. Reproduce the shown Satis configuration and verify that the PRIVATE-TOKEN header reaches the request; done means private GitLab repositories can be fetched using that token.

Written by the indexing model from the issue text.