function to generate Sha-256 in Kotlin

Sha256.kt

Class Hasher {
  fun hash(): String {
    val bytes = this.toString().toByteArray()
    val md = MessageDigest.getInstance("SHA-256")
    val digest = md.digest(bytes)
    return digest.fold("", { str, it -> str + "%02x".format(it) })
  }
}

You can replace the fold with toHexString() (Mind you that this is, as of the time of writing this, marked as ExperimentalStdlibApi):

fun String.hashedWithSha256() =
    MessageDigest.getInstance("SHA-256")
        .digest(toByteArray())
        .toHexString()

val hashed = "12345".hashedWithSha256() // "5994471abb01112afcc18159f6cc74b4f511b99806da59b3caf5a9c173cacfc5"