<header class="article-info clearfix">
  <h1 itemprop="name">
      <a href="{{ .Permalink }}" title="{{ .Title }}" itemprop="url">{{ .Title }}</a>
  </h1>
  <p class="article-author">By
    {{ if and (isset .Params "Author") (isset .Params "AuthorHomepage") }}
      <a href="{{ .Params.AuthorHomepage }}" title="{{ .Params.Author }}">{{ .Params.Author }}</a>
    {{ else }}
      <a href="{{ .Site.Params.AuthorHomepage }}" title="{{ .Site.Author.Name }}">{{ .Site.Author.Name }}</a>
    {{ end }}
  </p>
  <p class="article-time">
    <time datetime="{{ .Date }}" itemprop="datePublished">{{ .Date.Format .Site.Params.DateFormat }}</time>
  </p>
</header>

<header class="article-info clearfix">
  <h1 itemprop="name">
      <a href="{{ .Permalink }}" title="{{ .Title }}" itemprop="url">{{ .Title }}</a>
  </h1>
  <p class="article-author">By
    {{ if and (isset .Params "Author") (isset .Params "AuthorHomepage") }}
      <a href="{{ .Params.author_homepage }}" title="{{ .Params.author }}">{{ .Params.Author }}</a>
    {{ else }}
      <a href="{{ .Site.Params.AuthorHomepage }}" title="{{ .Site.Author.Name }}">{{ .Site.Author.Name }}</a>
    {{ end }}
  </p>
  <p class="article-time">
    <time datetime="{{ .Date }}" itemprop="datePublished">{{ .Date.Format .Site.Params.DateFormat }}</time>
  </p>
</header>

Change Author => author for post param
Change Author => author for post param