fun ObjectMapper.registerCreditsModule(): ObjectMapper {
    val credits = SimpleModule("credits")

    credits.addSerializer(SigningKey::class.java, SigningKeySerializer())
    credits.addDeserializer(SigningKey::class.java, SigningKeyDeserializer())

    credits.addSerializer(VerifyKey::class.java, VerifyKeySerializer())
    credits.addDeserializer(VerifyKey::class.java, VerifyKeyDeserializer())

    this.registerModule(credits)

    return this
}