ExchangeToken.scala

private def exchangeToken(token: String, userId: String): Future[TokenResponse] = {
  import io.circe.generic.auto._
  sttp
    .post(uri"${config.authServerUrl}/realms/${config.realm}/protocol/openid-connect/token")
    .body(
      "grant_type" -> "urn:ietf:params:oauth:grant-type:token-exchange",
      "client_id" -> config.clientId,
      "requested_subject" -> userId,
      "subject_token" -> token
    )
    .response(asJson[TokenResponse])
    .send()
    .flatMap {
      _.body match {
        case Left(error) => Future.failed(new RuntimeException(error))
        case Right(Left(circeError)) => Future.failed(circeError)
        case Right(Right(tokenResponse)) => Future.successful(tokenResponse)
      }
    }
}