How does one get an internal firmware notification when an external device reads a characteristic?

Question

I have a firmware build that uses the nRF52832 (SoftDevice S132) to return a variety of read characteristics to an external device. So far so good. I can verify that the values are read properly when using nRF connect or a mobile app. 
 How can I get some form of internal notification in firmware when an external devices READS one or more of these characteristics? 
 The application is to be able to flash an LED every time one of these read transactions occurs. 
 I have seen a few posts that suggest that "Authorized Reads" is the best approach for doing this but I haven't seen any clear concise code that demonstrates how this is performed. 
 Thanks for any advice.

TCdeveloper · Answer

I think Richard D.'s response was on the right track, although one doesn't have to provide any value. 
 I also think this link was helpful too: https://devzone.nordicsemi.com/f/nordic-q-a/9505/how-do-i-add-authorization-on-read-write-on-a-service-s-characteristics/35090#35090 
 
 Code that worked for me was: 
 
 ble_gatts_rw_authorize_reply_params_t auth_reply; 
 memset(&auth_reply, 0, sizeof(auth_reply)); 
 auth_reply.type = BLE_GATTS_AUTHORIZE_TYPE_READ; 
 auth_reply.params.write.gatt_status = BLE_GATT_STATUS_SUCCESS; 
 
 And then in the BLE event handler, add a case that looks like: 
 
 case BLE_GATTS_EVT_RW_AUTHORIZE_REQUEST: 
 sd_ble_gatts_rw_authorize_reply(m_conn_handle, &auth_reply); // Generic reply to allow read. 
 // Do anything else you want here. Strobe an LED etc... 
 break;