Hosters need to acquire a wildcard certificate or subject alternate name certificate and then use a host-named site collection URL policy that matches that certificate. For example, if a hoster acquires a *.contoso.com wildcard certificate, the hoster has to generate host-named site collection URLs such as https://site1.contoso.com, https://site2.contoso.com, and so on, to enable these sites to pass browser SSL validation. However, if customers require unique second-level domain names for their sites, the hoster has to create multiple Web applications rather than multiple host-named site collections.
To configure SSL for host-named site collections, enable SSL when creating the Web application. This will create an IIS Web site with an SSL binding instead of an HTTP binding. After the Web application is created, open IIS Manager and assign a certificate to that SSL binding. You can then create site collections in that Web application.