Should the authority host be read from the environment variable AZURE_AUTHORITY_HOST if the user doesn't pass it in the options?

[ahsonkhan]

We currently default the authority host within the options which are used in the various credentials we have, and don't read it from the environment variable on behalf of the user.

azure-sdk-for-cpp/sdk/identity/azure-identity/inc/azure/identity/client_certificate_credential.hpp

Lines 43 to 53 in 69e5f1a

	struct ClientCertificateCredentialOptions final : public Core::Credentials::TokenCredentialOptions
	{
	/**
	* @brief Authentication authority URL.
	* @note Default value is Azure AD global authority (https://login.microsoftonline.com/).
	*
	* @note Example of an authority host string: "https://login.microsoftonline.us/". See national
	* clouds' Azure AD authentication endpoints:
	* https://docs.microsoft.com/azure/active-directory/develop/authentication-national-cloud.
	*/
	std::string AuthorityHost = _detail::ClientCredentialCore::AadGlobalAuthority;

This is different from behaviors in other languages, like Go and .NET.
https://github.com/Azure/azure-sdk-for-net/blob/d90042d570a6531d7f7ed97e82ddfe95c730158b/sdk/identity/Azure.Identity/src/Credentials/TokenCredentialOptions.cs#L25-L32
https://github.com/Azure/azure-sdk-for-go/blob/514985a4c9d311c90b86c74c6ff779abcec1ffcd/sdk/azidentity/azidentity.go#L107-L111

Should we match the precedence and consider reading the environment variable on behalf of the user, if they don't provide an option and ? If so, we'd want to design a solution that's non-breaking, because we can't use "is the option not set" as a sentinel to read the environment variable.

cc @antkmsft, @LarryOsterman

[joshfree]

Related

• Add AZURE_AUTHORITY_HOST env var details azure-sdk-for-net#36001