Combining Curl Post with Request Queue Kotlin Android

Question

The following works with the REST api, however I am now trying to achieve the same in Android Kotlin

curl -X POST \
    -H 'content-type:application/json' \
    -d '{"userid":"testid","first_name":"test_first_name"}' \
    http://localhost:5000/users

My attempt to call the same curl in kotlin:

    fun submit_new_user(view: View) {
        val textView = findViewById<TextView>(R.id.textView111)
        // ...
        // Instantiate the RequestQueue.
        val queue = Volley.newRequestQueue(this)
        //build the curl
        val requestBody = "userid=testid" + "&first_name=test_first_name"
        // Request a string response from the provided URL.
        val url = "http://localhost:5000/users?" + requestBody
        val stringRequest = StringRequest(
            Request.Method.POST, url,
            Response.Listener<String> { response ->
                // Display the first 500 characters of the response string.
                textView.text = "Response is: ${response.substring(0, 20)}"
            },
            Response.ErrorListener { textView.text = "That didn't work!" } )
        // Add the request to the RequestQueue.
        queue.add(stringRequest)
    }

Also can anyone explain a few security issues

Answer 1

Got it working by using this solution from another question,

https://stackoverflow.com/a/40118803/2203917

        val textView = findViewById<TextView>(R.id.textView111)
        val url = "http://localhost:5000/users"
        val sr: StringRequest = object : StringRequest(
            Method.POST, url,
            Response.Listener { response -> textView.text = "Response is: ${response.substring(0, 20)}" },
            Response.ErrorListener { error -> textView.text = "That didn't work!"  }) {
            @Throws(AuthFailureError::class)
            override fun getBody(): ByteArray {
                val params2 = HashMap<String?, String?>()
                params2["userid"] = "testid"
                params2["email_address"] = "testemail@example.com"
                return JSONObject(params2 as Map<*, *>).toString().toByteArray()
            }
            override fun getBodyContentType(): String {
                return "application/json"
            }
        }
        // Add the request to the RequestQueue.
        Volley.newRequestQueue(this).add(sr)

Please comment if any security issues could be improved.