The unavailable credential type is Secret key. In the Cohesity NetBackup Web UI Cloud Administrator's Guide topic "Add a cloud provider for a Snapshot Manager," the Microsoft Azure configuration table identifies the supported credential types as Application service principal, System managed identity, and User managed identity. For an Application service principal, the wizard requires related parameters such as Tenant ID, Client ID, and Secret key; however, Secret key is listed as a field used by the application service principal, not as an independent credential type. Cohesity describes the secret key simply as "the secret key of the application," while the actual credential type heading remains Application service principal. The same table separately lists System managed identity, which requires enabling system-managed identity on the Snapshot Manager host in Azure and assigning the role, and User managed identity, which uses the Client ID of the user-managed identity connected to the Snapshot Manager host. Therefore, options A, B, and D are valid Azure Snapshot Manager credential types, while option C is only an authentication parameter under service- principal configuration. Reference topics: NetBackup Web UI Cloud Administrator's Guide, Configure Snapshot Manager in NetBackup, and Add a cloud provider for a Snapshot Manager.