Maximum number of domains supported in Azure Websites

We're building a hosted service where each of our users gets a custom sub domain on our service's domain when they sign up (for example `john.myservice.com`). We handled this by adding a wildcard entry in our Azure Website's domain manager (`*.myservice.com`) and Azure Websites would now correctly handle all sub domains of the domain we added. However, we also allow our users to map their own custom domains to their sub domain (for example: `johnsmith.com` points to `john.myservice.com`). Right now we've achieved this by adding an A Record to `johnsmith.com`'s DNS pointing to the Azure Websites IP Address, and have added `johnsmith.com` as an additional domain in Azure Websites' domain manager. So far, this is working as expected. My question is how many such domains does Azure Websites support? Say we have a million users who each want to map their custom domains to their hosted sub domain. Does Azure have a hard limit on the number of fully qualified domains that can be mapped to a website? On a related note, what would be the best way to go about this on a Azure Website. I'm sure there are other approaches apart from the one we are using right now.