Generates a SAS Token for Azure REST Api Calls (Particularly for Service Bus Services like Event Hub & Queues) in Kotlin

SAStoken.kt

import java.net.URLEncoder
import java.time.Instant
import java.util.*
import javax.crypto.Mac
import javax.crypto.spec.SecretKeySpec

const val ONE_HOUR = 3600L;

/**
 *
 * Code  for generating of SAS token for authorization with Service Bus in Kotlin
 *
 * based on: https://gist.github.com/sedouard/79d9813bfae0ed1e56cf for C#
 *
 * @param resourceUri e.g. https://tripappservicebus.servicebus.windows.net/mediaservicequeue/messages
 * @param key e.g. tZkUg3JERVurvDU8Ra+DUC7VTTAT6P3zi7xD8gALdXU=
 */
fun generateSasToken(resourceUri: String, key: String, policy: String = "RootManageSharedAccessKey", expiryInSeconds: Long = ONE_HOUR): String
{
    val expiry = Instant.now().epochSecond + expiryInSeconds
    val resourceUrl = URLEncoder.encode(resourceUri, Charsets.UTF_8.name())
    val stringToSign = resourceUrl + "\n$expiry"
    val hmac = Mac.getInstance("HmacSHA256").apply {
        init(SecretKeySpec(key.toByteArray(Charsets.UTF_8), algorithm));
    }

    val signature = Base64.getEncoder().encodeToString(hmac.doFinal(stringToSign.toByteArray()));
    val signatureUrl = URLEncoder.encode(signature, Charsets.UTF_8.name())
    return "SharedAccessSignature sr=$resourceUrl&sig=$signatureUrl&se=$expiry&skn=$policy"
}