Get value from HTTP POST request body

this is just an example. it may not be fully correct.

 configuration

root@(ve11b)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm virtual bar
ltm virtual bar {
    destination 172.28.24.10:80
    ip-protocol tcp
    mask 255.255.255.255
    profiles {
        http { }
        tcp { }
    }
    rules {
        qux
    }
    source 0.0.0.0/0
    vs-index 2
}
root@(ve11b)(cfg-sync In Sync)(Active)(/Common)(tmos) list ltm rule qux
ltm rule qux {
    proc key2value {l k} {
  foreach elm [split $l ,] {
    set kv [split $elm :]
    if { $k eq [string trim [lindex $kv 0] { }] } {
      return [string trim [lindex $kv 1] { }]
    }
  }
}
when HTTP_REQUEST {
  HTTP::collect [HTTP::header Content-Length]
}
when HTTP_REQUEST_DATA {
  set payload [HTTP::payload]
  log local0. "payload=$payload "
  log local0. "username=[call key2value [lindex $payload 0] \\"username\\"]"
  log local0. "password=[call key2value [lindex $payload 0] \\"password\\"]"
  HTTP::release
}
}

 client

[root@centos1 ~] curl -X POST -H "Content-type: application/json" -d '{\"username\" : \"abc\", \"password\" : \"def\"}' http://172.28.24.10
curl: (52) Empty reply from server
[root@centos1 ~]

 /var/log/ltm

[root@ve11b:Active:In Sync] config  tail -f /var/log/ltm
Feb 19 19:38:15 ve11b info tmm1[14140]: Rule /Common/qux : payload={\"username\" : \"abc\", \"password\" : \"def\"}
Feb 19 19:38:15 ve11b info tmm1[14140]: Rule /Common/qux : username=\"abc\"
Feb 19 19:38:15 ve11b info tmm1[14140]: Rule /Common/qux : password=\"def\"