InstallUtility failing to create AD Application with IdentifierUri 'SignService'

[robot-o]

When attempting to set up the SignService using the InstallUtility as outlined in the Deployment.md documentation, after cloning, building, running and logging in the application crashes with an unhandled exception:

DataServiceClientException: {"odata.error":{"code":"Request_BadRequest","message":{"lang":"en","value":"Values of identifierUris property must use a verified domain of the organization or its subdomain: 'https://SignService/uuid'"},"requestId":"requestid","date":"2022-03-18T13:17:10","values":[{"item":"PropertyName","value":"identifierUris"},{"item":"PropertyErrorCode","value":"HostNameNotOnVerifiedDomain"},{"item":"HostName","value":"https://SignService/uuid"}]}}

apparently the default IdentifierUris value https://SignService/<uuid> as defined in https://github.com/dotnet/SignService/blob/9560fc6f77bf1bfd013d557a53549b95e634cd3f/src/InstallUtility/Program.cs#L486-L489 won't work unless it's present in aad / custom domains.

when we changed it to a custom domain that is present as at least 'verified' in AAD -> Custom Domains, the creation of the Application succeeded.

are we supposed to edit the Program.cs to add the uri there or did the IdentifierUris value https://SignService/GUID get accepted by AAD at some point in the past and a platform change has caused this exception to be thrown?