How does someone get a jira[.]com subdomain? How common is this?
There are a few out there. I believe that they are legacy instances (from JIRA Studio).
JIRA passes the base url to you at installation (and I want to say it’s in the query string on page request) - use that. Don’t hard code or you’ll have problems when CLOUD-6999 is resolved (or Atlassian adds another top level domain).