概要

KotlinでCookieを扱うサンプルコードです(値の設定、取り出し、消去)
WebViewや認証処理で活用できると思います。
本文

package jp.co.cookietest

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.util.Log
import android.webkit.CookieManager
import jp.co.cookietest.databinding.ActivityMainBinding

class MainActivity : AppCompatActivity() {
    private lateinit var binding: ActivityMainBinding
    private val cookieManager = CookieManager.getInstance()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        val view = binding.root
        setContentView(view)

        val url: String = "https://www.yahoo.co.jp/"
        binding.button1.setOnClickListener {
            Log.w("TAG", "cookieに値を設定します")
            setCookie(url, "count", "15")
        }
        binding.button2.setOnClickListener {
            Log.w("TAG", getCookie(url))
        }
        binding.button3.setOnClickListener {
            Log.w("TAG", "cookieを全て消去します")
            removeAllCookies()
        }
    }

    private fun setCookie(url: String, cookieName: String, cookieValue: String) {
        val cookieString = "$cookieName=$cookieValue;"
        cookieManager.setCookie(url, cookieString)
        cookieManager.flush()
    }

    private fun getCookie(url: String): String {
        return cookieManager.getCookie(url) ?: "cookieは空っぽです"
    }

    private fun removeAllCookies() {
        cookieManager.removeAllCookies(null)
    }
}