customOptions :: Options
customOptions = defaultOptions
  { fieldLabelModifier      = tail
  , constructorTagModifier  = map toLower
  , unwrapUnaryRecords      = True
  }

data Auth = Auth
  { _username :: String
  , _password :: String
  } deriving (Generic, Show)

instance ToJSON Auth where
    toEncoding = genericToEncoding customOptions
instance FromJSON Auth where
  parseJSON = genericParseJSON customOptions


-- res <- post url (toJSON auth)
-- vs.
-- res <- post url (encode auth)