title: Firebase multi-domain support to one instance
body: <p> I'm hoping to use Firebase to create an application that will allow users to make their content accessible via a custom domain. This is probably best described as a similar setup to how <a href="https://wordpress.org/support/article/wordpress-multisite-domain-mapping/" rel="nofollow noreferrer">WordPress Multisite Domain Mapping</a> works where there would be a main site, <code>domain.com</code> and many subsites based on their content <code>customdomain.com</code> <code>mydomain.com</code> <code>anotherdomain.com</code>.</p>
  
  <p>The domains (100+) would point to the same codebase + Firestore, but based on the domain - would serve different content. All content swapping would be stored within a cloud function to serve the appropriate site.</p>
  
  <p>I did see <a href="https://support.google.com/cloud/answer/7650096?hl=en" rel="nofollow noreferrer">this domain limit exceeded FAQ</a> but I wasn't sure if that applies to what I'm attempting to do at a DNS level.</p>
  
  <p>I'm currently doing this in an older version of the app with DigitalOcean and an individual CloudFlare site that points to the same server, but it's a major pain to setup Page Rules, SSLs, etc instead of something that could hopefully be automated.</p>
  
  <p>Thanks for any info!</p>