[FEATURE REQ] Support setAuthorityHost with CredentialBuilderBase

[jongio]

Right now, it doesn't look like you can call setAuthorityHost with DefaultAzureCredentialBuilder:
https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/identity/azure-identity/src/main/java/com/azure/identity/DefaultAzureCredentialBuilder.java

Which implements CredentialBuilderBase

CredentialBuilderBase doesn't expose setAuthorityHost
https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/identity/azure-identity/src/main/java/com/azure/identity/CredentialBuilderBase.java

EnvironmentCredentialBuilder does expose setAuthorityHost

https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/identity/azure-identity/src/main/java/com/azure/identity/EnvironmentCredentialBuilder.java

I recommend implementing this at the CredentialBuilderBase level.

Because ManagedIdentityCredential and other credential classes need this as well

https://github.com/Azure/azure-sdk-for-java/blob/master/sdk/identity/azure-identity/src/main/java/com/azure/identity/ManagedIdentityCredentialBuilder.java

! This is currently blocking use of DefaultAzureCredentialBuilder with other clouds, such as Azure Government.

[jongio]

Workaround using reflection:

IdentityClientOptions options = new IdentityClientOptions().setAuthorityHost("https://login.microsoftonline.us/");
DefaultAzureCredentialBuilder cred = new DefaultAzureCredentialBuilder();
Field identityClientOptions = cred.getClass().getSuperclass().getDeclaredField("identityClientOptions");
identityClientOptions.setAccessible(true);
identityClientOptions.set(cred, options);

KeyClient keyClient = new KeyClientBuilder().vaultUrl(dotenv.get("AZURE_KEYVAULT_URL"))
                .credential(cred.build()).buildClient();

Or use EnvironmentCredentialBuilder instead of DefaultAzureCredentialBuilder

 KeyClient keyClient = new KeyClientBuilder().vaultUrl(dotenv.get("AZURE_KEYVAULT_URL"))
  .credential(new EnvironmentCredentialBuilder().authorityHost("https://login.microsoftonline.us/").build()).buildClient();

[g2vinay]

This Issue was resolved in this PR: #8765
The authorityHost setter was added to DefaultAzureCredentialBuilder.
MI credential doesn't consume authHost, so that's still excluded.