As part of the work on testing the support for HTTP/2 through the SDK we have identified that the list of hostnames is hardcoded in the current Java SDK.
Meaning that customizing the client creation will not be enough to call the test endpoint as it doesn't belong to any of the hardcoded hostnames.

On Go SDK we can do that by adding the following:

NewAzureIdentityAuthenticationProviderWithScopesAndValidHosts(yourCrendential, yourScopes, []string{"microsoftgraphvalidation.ags.msidentity.com"})

We should have a similar experience in providing ways for customers to use Java SDK when testing their applications within HTTP/2 by adding the capability of changing the hostname.