Simple class to get access token based on service key

GoogleAPIServiceAccountAuth.scala

import java.io.{IOException, StringReader, Reader, ByteArrayInputStream}
import java.nio.charset.Charset
import java.security.{NoSuchAlgorithmException, KeyFactory, PrivateKey}
import java.security.spec.{InvalidKeySpecException, PKCS8EncodedKeySpec}
import java.util.Collections

import com.google.api.client.json.webtoken.{JsonWebToken, JsonWebSignature}
import com.google.api.client.json.{JsonFactory, GenericJson, JsonObjectParser}
import com.google.api.client.json.jackson2.JacksonFactory
import com.google.api.client.util.{SecurityUtils, PemReader, Joiner}
import com.google.api.services.androidpublisher.AndroidPublisherScopes

class ServiceAccountApiAccess {
  val jsonKey = """{
  "type": "service_account",
  "project_id": "project-XXXXXXX",
  "private_key_id": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
  "private_key": "-----BEGIN PRIVATE KEY-----\nXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n-----END PRIVATE KEY-----\n",
  "client_email": "[email protected]",
  "client_id": "zzzzzzzzzzzzzzzzzzzzzzzzzzzz",
  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
  "token_uri": "https://accounts.google.com/o/oauth2/token",
  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/[email protected]"
} """

  val credentialStream = new ByteArrayInputStream(jsonKey.getBytes())
  val parser: JsonObjectParser = new JsonObjectParser(JacksonFactory.getDefaultInstance())
  val fileContents: GenericJson = parser.parseAndClose(credentialStream, Charset.forName("UTF-8"), classOf[GenericJson])
  val clientId: String = fileContents.get("client_id").asInstanceOf[String]
  val clientEmail: String = fileContents.get("client_email").asInstanceOf[String]
  val privateKeyPem: String = fileContents.get("private_key").asInstanceOf[String]
  val privateKeyId: String = fileContents.get("private_key_id").asInstanceOf[String]

  
  val privateKey: PrivateKey = privateKeyFromPkcs8(privateKeyPem)
  val header: JsonWebSignature.Header = new JsonWebSignature.Header
  header.setAlgorithm("RS256")
  header.setType("JWT")
  header.setKeyId(privateKeyId)
  val payload: JsonWebToken.Payload = new JsonWebToken.Payload
  val currentTime: Long = System.currentTimeMillis()
  payload.setIssuer(clientEmail)
  payload.setAudience("https://www.googleapis.com/oauth2/v4/token")
  payload.setIssuedAtTimeSeconds(currentTime / 1000)
  payload.setExpirationTimeSeconds(currentTime / 1000 + 3600)
  payload.setSubject(null)

  payload.put("scope", Joiner.on(' ').join(Collections.singleton(AndroidPublisherScopes.ANDROIDPUBLISHER)))
  val jsonFactory: JsonFactory = JacksonFactory.getDefaultInstance
  try{
    var assertion: String = JsonWebSignature.signUsingRsaSha256(privateKey, jsonFactory, header, payload)
    println(assertion)
  }catch {
    case ex:Exception => ex.printStackTrace()
  }


  def  privateKeyFromPkcs8(privateKeyPem: String):PrivateKey = {
    val reader: Reader = new StringReader(privateKeyPem)
    val section: PemReader.Section = PemReader.readFirstSectionAndClose(reader, "PRIVATE KEY")
    if (section == null) {
      throw new IOException("Invalid PKCS8 data.")
    }
    val bytes: Array[Byte] = section.getBase64DecodedBytes
    val keySpec: PKCS8EncodedKeySpec = new PKCS8EncodedKeySpec(bytes)
    var unexpectedException: Exception = null
    try {
      val keyFactory: KeyFactory = SecurityUtils.getRsaKeyFactory
      val privateKey: PrivateKey = keyFactory.generatePrivate(keySpec)
      privateKey
    }
    catch {
      case exception: NoSuchAlgorithmException => {
        unexpectedException = exception
      }
      case exception: InvalidKeySpecException => {
        unexpectedException = exception
      }
    }
    val keyFactory: KeyFactory = SecurityUtils.getRsaKeyFactory
    val privateKey: PrivateKey = keyFactory.generatePrivate(keySpec)
    privateKey
  }
}