Default hostname changes (azurewebsites.net)

[mathewc]

The App Service platform is moving to a strategy where the default hostname for a site will vary regionally. This means that code can't simply assume "azurewebsites.net".

New default hostname format: siteName-<dnlHash>.<region>.azurewebsites.net​
SCM site will have this format:​ siteName-<dnlHash>.scm.<region>.azurewebsites.net

There are several known places in the host currently where we're using this string literal. We'll need to review all these and make changes as required. These include:

• In defaulting the hostname used by the Host ID provider for Linux Dedicated (code here)
• In constructing the Host ID for Linux Consumption (code here)
  • Note: there's already a related issue for this [Linux Consumption] HostId generation logic should be cloud specific #8788.
  • We might just be able to live with the existing code since it still technically works, even with the new hostname format.
  • Any changes to the Host ID format for existing apps would of course be breaking.
• In the JWT issuer/audience values (code here). These aren't a problem and would be difficult to change anyways, since the App Service platform and Kudu are using these same values and rely on this contract.
• FunctionsSyncManager uses the hostname to make Front End settriggers calls (code here). We need to make sure that the hostname value returned by the HostNameProvider is correct in all cases for these calls to work. For Linux Dedicated, I see there's already a problem - for that platform WEBSITE_HOSTNAME isn't set (at least it wasn't when the code was written), so it hardcodes "azurewebsites.net". This will need to change.

Note that