Proof Key for Code Exchange (PKCE) for OAuth 2.0

pkce.main.kts

#!/usr/bin/env kotlin

import java.security.MessageDigest
import java.util.Base64
import kotlin.random.Random

/**
 * Proof Key for Code Exchange (PKCE) for OAuth 2.0
 */
fun pkce() {
  val secureRandom: ByteArray = Random.nextBytes(32)
  val verifier: String = secureRandom.toSha256Hash()
  println("code_verifier: $verifier")

  val challenge: String = verifier.toSha256Hash()
  println("code_challenge: $challenge")
}

// region helper extension methods

/**
 * Returns a `SHA-256` encoded string from an input string.
 */
fun String.toSha256Hash(): String {
  return this.toByteArray().toSha256Hash()
}

/**
 * Returns a `SHA-256` encoded string from an input byte array.
 */
fun ByteArray.toSha256Hash(): String {
  val sha256: MessageDigest = MessageDigest.getInstance("SHA-256")
  val hash: ByteArray = sha256.digest(this)
  return Base64.getUrlEncoder().withoutPadding().encodeToString(hash)
}

// endregion

pkce()