A method, system and computer program product are provided for implementing block extent granularity authorization command flow processing for a Coherent Accelerator Processor Interface (CAPI) adapter. An Application Client builds a command including start LBA and number of LBAs and Child Authorization Handle. The Application Client sends the command directly to the CAPI Adapter via the Application Clients CAPI Server Registers assigned to the specific Application Client. The CAPI adapter validate that the requesting Client is authorized to perform the command using the Authorization Handle and the receiving CAPI Server Register address. The CAPI Adapter executes the validated command and sends completion back to the Application Client.