A method, system and computer program product are provided for implementing block extent granularity authorization model processing in Coherent Accelerator Processor Interface (CAPI) adapters. The CAPI adapter includes an authorization table and a file system authorization function to authenticate data access for a client at an extent granularity and to prevent an application from accessing unauthorized data in the CAPI adapter. Each authorization table entry provides for the CAPI client, a CAPI client identification (ID), a CAPI server register space assigning resource ownership to the CAPI client with a CAPI set of allowed functions.