A quick script to convert JWK public keys to .pem files

jwk-to-pem.scala

load.ivy("com.nimbusds" % "nimbus-jose-jwt" % "4.21")
load.ivy("org.bouncycastle" % "bcprov-jdk15on" % "1.51")

@

import com.nimbusds.jose.jwk._
import org.bouncycastle.util.io.pem._
import java.io._

def main(input: String) = {
  val set = JWKSet.load(new File(input))

  // currently hard-coded for RSA keys
  val matcher = (new JWKMatcher.Builder).publicOnly(true).keyType(KeyType.RSA).keyUse(KeyUse.SIGNATURE).build
  val key = (new JWKSelector(matcher)).select(set).get(0).asInstanceOf[RSAKey].toPublicKey

  val output = new StringWriter
  val pemWriter = new PemWriter(output)
  val pem = new PemObject("RSA PUBLIC KEY", key.getEncoded)
  pemWriter.writeObject(pem)
  pemWriter.close()

  println(output.toString)
}