HmacGenerator for Coupang partners with Kotlin

HmacGenerator.kt

import org.apache.commons.codec.binary.Hex
import java.nio.charset.Charset
import java.security.GeneralSecurityException
import java.text.SimpleDateFormat
import java.util.*
import javax.crypto.Mac
import javax.crypto.spec.SecretKeySpec

object HmacGenerator {
    private const val EXCEPTION_MESSAGE = "incorrect uri format"
    private const val SPLIT_TEXT = "\\?"
    private const val EMPTY_TEXT = ""
    private const val DATE_FORMAT = "yyMMdd'T'HHmmss'Z'"
    private const val ALGORITHM = "HmacSHA256"
    private const val ALGORITHM_FORMAT = "CEA algorithm=%s, access-key=%s, signed-date=%s, signature=%s"
    private val STANDARD_CHARSET = Charset.forName("UTF-8")


    fun generate(method: String, uri: String, secretKey: String, accessKey: String): String {
        val parts = uri.split(SPLIT_TEXT)
        if (parts.size > 2) {
            throw RuntimeException(EXCEPTION_MESSAGE)
        }
        val path = parts[0]
        val query = if (parts.size == 2) parts[1] else EMPTY_TEXT

        val dateFormatGmt = SimpleDateFormat(DATE_FORMAT).also { it.timeZone = TimeZone.getTimeZone("GMT") }
        val datetime = dateFormatGmt.format(Date())
        val message = datetime + method + path + query

        val signature: String = try {
            val signingKey = SecretKeySpec(secretKey.toByteArray(STANDARD_CHARSET), ALGORITHM)
            val mac = Mac.getInstance(ALGORITHM).apply { init(signingKey) }
            val rawHmac = mac.doFinal(message.toByteArray(STANDARD_CHARSET))
            Hex.encodeHexString(rawHmac)
        } catch (e: GeneralSecurityException) {
            throw IllegalArgumentException()
        }
        return String.format(ALGORITHM_FORMAT, ALGORITHM, accessKey, datetime, signature)
    }
}