<p class="author">
    {{ if (isset .Params "authors") }}
        {{ $authsCount := .Params.authors | len }}
        {{ $commaCount := sub $authsCount 2 }}
        {{ range $i, $author := .Params.authors -}}
            <a href="/tags/{{ $author | urlize }}">{{ $author }}</a>{{ if le $i $commaCount }},{{ end }}
        {{ end }}
    {{ else }}
        <a href="/tags/{{ .Params.author | urlize }}">{{ .Params.author }}</a>
    {{ end }}
</p>