circe

scala> import com.typesafe.config.ConfigFactory
scala> import io.circe.generic.auto._
scala> import io.circe.config.syntax._
scala> case class ServerSettings(host: String, port: Int, ssl: Option[String])
scala> case class HttpSettings(server: ServerSettings, version: Double)
scala> case class AppSettings(http: HttpSettings)
scala> val config = ConfigFactory.parseString("http { version = 1.1, server { host = localhost, port = 8080 } }")
scala> config.as[ServerSettings]("http.server")
res0: Either[io.circe.Error, ServerSettings] = Right(ServerSettings(localhost,8080,None))
scala> config.as[HttpSettings]("http")
res1: Either[io.circe.Error, HttpSettings] = Right(HttpSettings(ServerSettings(localhost,8080,None),1.1))
scala> config.as[AppSettings]
res2: Either[io.circe.Error, AppSettings] = Right(AppSettings(HttpSettings(ServerSettings(localhost,8080,None),1.1)))
scala> import cats.effect.IO
scala> config.asF[IO, AppSettings]
res3: IO[AppSettings] = IO(AppSettings(HttpSettings(ServerSettings(localhost,8080,None),1.1)))
scala> import io.circe.config.parser
scala> val settings = parser.decodeF[IO, AppSettings]()
scala> settings.unsafeRunSync()
res4: AppSettings = AppSettings(HttpSettings(ServerSettings(localhost,8080,None),1.1))