{{ authors scope="auth" }}
    <h2>Contributions from {{ name }}:</h2>
    {{ contribution_options }}
        <label class="flex choose">
            <input type="checkbox" 
              name="authors[{{ auth:index }}][contributions][{{ index }}]" 
              value="{{ value }}" />
            <span>{{ value }}</span>
        </label>
    {{ /contribution_options }}
{{ /authors }}

renders as:

<h2>Contributions from Daniel Fowler:</h2>
<label class="flex choose">
    <input type="checkbox" name="authors[][contributions][1]" value="Music">
    <span>Music</span>
</label>
<label class="flex choose">
    <input type="checkbox" name="authors[][contributions][2]" value="Lyrics">
    <span>Lyrics</span>
</label>
<label class="flex choose">
    <input type="checkbox" name="authors[][contributions][3]" value="Text">
    <span>Text</span>
</label>

Statamic 2.10.5