How do set SNMP V3 user name and password on openwrt

My openwrt supports SNMP V1/V2. However, there are problems in setting up SNMP V3.
I know that SNMPd. conf is generated by /etc/config/snmpd , I tried to set up the SNMP V3 username and password configuration but failed.

Can you show your configs...and perhaps links to documentation regarding V3?

Here is my configuration:

  1. config /etc/config/snmpd
    config createUser rw_createUser
    option username 'rwUser'
    option verifmode 'SHA'
    option verifcode 'apassword'
    option encrymode 'AES'
    option encrykey 'ppassword'

config createUser ro_createUser
option username 'roUser'
option verifmode 'SHA'
option verifcode 'apassword'
option encrymode 'AES'
option encrykey 'ppassword'
2. config /etc/init.d/snmpd
snmpd_createuser_add(){
local cfg="$1"

config_get username "$cfg" username                 
[ -n "$username" ] || return 0                      
config_get verifmode "$cfg" verifmode                                               
[ -n "$verifmode" ] || return 0                        
config_get verifcode "$cfg" verifcode                  
[ -n "$verifcode" ] || return 0                                                     
config_get encrymode "$cfg" encrymode                                               
[ -n "$encrymode" ] || return 0                        
config_get encrykey "$cfg" encrykey             
[ -n "$encrykey" ] || return 0                                                      
                                                           
echo "createUser $username $verifmode $verifcode $encrymode $encrykey" >> $RUN_C    

}
config_foreach snmpd_createuser_add createUser