Feature code + Class of Service implementation to allow certain users to spy/whisper/barge on a specified extension. Based on Lgaetz original targeted spy, but allowing user permissions to be set with COS module on FPBX

targeted ChanSpy with permissions

;  Feature code + Class of Service implementation to allow certain users to spy/whisper/barge on
;  a specified extension. 
; 
; Latest version:
;      https://gist.github.com/hgaibor/82433116540f15ab345b2914500abb0d
; 
; Forked original version:
;      https://gist.github.com/lgaetz/78c4e114952e79596c1ed4123559d3d3
;
; Usage and install instructions: 
;   1. On FreePBX/PBXact GUI, Create a Custom Destination that points to the [custom-spy-with-cos] context0.
;      Fill the interface fields with the values after the --> : 
;       1.1 Target --> custom-spy-with-cos,s,1
;       1.2 Description --> Put a brief description
;       1.3 Notes --> Put your detailed comments here
;       1.4 Return --> no
;
;   2. Create a Misc Application that will point to created custom destination above. 
;      This destination will have the feature code you choose and will allow you to set the permissions over the 
;      Class of Service module. 
;       2.1 Enable --> Yes
;       2.2 Description --> Spy with permissions feature code
;       2.3 Feature Code --> *557
;       2.4 Destination --> SELECT Custom Destination created above
;      
;   3. Create Class of Service rules to DENY all users to use this code and allow the ones you need.
;      Since you used the Misc Application module to assign the feature code, it will appear under the
;      Class of Service --> [Feature codes] tab
;      
;   4. Put Custom Dialplan at (GUI can be used using Config edit module):
;      /etc/asterisk/extensions_custom.conf 
;   Dial feature code assigned under Misc Application to start in spy mode. While spying on 
;   active channel use the following dtmf input to toggle modes:
;         dtmf 4 - spy mode
;              5 - whisper mode 
;              6 - barge mode
; 
;   This is default behavior mentioned in https://wiki.asterisk.org/wiki/display/AST/Application_ChanSpy
;
; License:  GNU GPL2
;
; Version History
;      2021-03-08 First public commit by hgaibor


[custom-spy-with-cos]
exten => s,1,Noop(Entering user defined context custom-spy-with-cos in extensions_custom.conf)
exten => s,n,Read(spyee,please-enter-the&extension&number&followed_pound)
exten => s,n,GoTo(targeted-chanspy,${spyee},1)

[targeted-chanspy]
exten => _.,1,Noop(Entering user defined context targeted-chanspy in extensions_custom.conf)
exten => _.,n,Set(TIMEOUT(absolute)=3600)   ; prevent hung channel by setting 1 hour timeout recommended if using infinite loop
exten => _.,n,Answer
exten => _.,n(once-upon-a-time),Wait(1)
exten => _.,n,set(spy_target=)   ; initialize target var
; get list of dialable devices for extension
exten => _.,n,Set(DEVS=${DB(AMPUSER/${EXTEN}/device)})   ;  & delimited list of devices
exten => _.,n,Set(DEVS=${STRREPLACE(DEVS,&,\,)})           ;  comma delimited list of devices
; step thru each device and look for an active channel
exten => _.,n,While($["${SET(DEV=${POP(DEVS)})}" != ""])
exten => _.,n,noop(dev: ${DEV})
; using a regex of SIP/${EXTEN}- will match both SIP and PJSIP channels, and the trailing - character should
; help to ensure there is only a single match. If multiple channels are returned the chanspy application will fail
exten => _.,n,set(spy_target=${CHANNELS(SIP/${DEV}-)})  
exten => _.,n,ExecIf($["${spy_target}"!=""]?ExitWhile)  ; if an active channel is found exit the loop
exten => _.,n,EndWhile()
exten => _.,n,ExecIF($["${spy_target}"!=""]?ChanSpy(${spy_target},dnqE))    ; q option suppresses channel announce on barge

exten => _.,n,Hangup()      ;comment this line with a semicolon to do infinite loop
exten => _.,n,GoTo(once-upon-a-time)
exten => _.,n,Hangup()
exten => h,1,Hangup()
exten => s,1,Hangup()
exten => T,1,Hangup()   ; timeout destination

Great stuff, thanks Hugo!