Springer have solved the "several authors" problem by repeating the citation_author meta tag as many times as there are authors.
For example, https://link.springer.com/article/10.1007/s00445-015-0960-9 offers the following author information:
<meta name="citation_author" content="Céline M. Vidal"/> <meta name="citation_author_institution" content="Université Paris Diderot"/> <meta name="citation_author_email" content="vidal@ipgp.fr"/> <meta name="citation_author" content="Jean-Christophe Komorowski"/> <meta name="citation_author_institution" content="Université Paris Diderot"/> <meta name="citation_author" content="Nicole Métrich"/> <meta name="citation_author_institution" content="Université Paris Diderot"/> <meta name="citation_author" content="Indyo Pratomo"/> <meta name="citation_author_institution" content="Badan Geologi"/> <meta name="citation_author" content="Nugraha Kartadinata"/> <meta name="citation_author_institution" content="Badan Geologi"/> <meta name="citation_author" content="Oktory Prambada"/> <meta name="citation_author_institution" content="Badan Geologi"/> <meta name="citation_author" content="Agnès Michel"/> <meta name="citation_author_institution" content="Université Paris Diderot"/> <meta name="citation_author" content="Guillaume Carazzo"/> <meta name="citation_author_institution" content="Université Paris Diderot"/> <meta name="citation_author_institution" content="Institut de Physique du Globe"/> <meta name="citation_author" content="Franck Lavigne"/> <meta name="citation_author_institution" content="Université Paris 1 Panthéon-Sorbonne"/> <meta name="citation_author" content="Jessica Rodysill"/> <meta name="citation_author_institution" content="Brown University"/> <meta name="citation_author" content="Karen Fontijn"/> <meta name="citation_author_institution" content="University of Oxford"/> <meta name="citation_author_institution" content="Ghent University"/> <meta name="citation_author" content="Surono"/> <meta name="citation_author_institution" content="Badan Geologi"/>