I am trying to understand Ktor form authentication. To do so, I have created a very simple web app but I am stuck on an error for multiple hours and documentation seems incomplete or outdated.

fun Application.bank() {
    install(Authentication) {
        form("form") {
            challenge = FormAuthChallenge.Unauthorized
            passwordParamName = "password"
            userParamName = "username"
            validate { credentials ->
                println("Credentials : ${credentials.name}, ${credentials.password}")
                when {
                    credentials.name == "John" && credentials.password == "pa$$w0rd" -> UserIdPrincipal("John")
                    else -> null
                }
            }
        }
    }
    routing {
        authenticate("form") {
            route("account") {
                post {
                    call.respond(HttpStatusCode.OK, "connected")
                }
            }
        }
    }
}

To access the route /account I send this HTTP request :

POST <http://0.0.0.0:8081/account?username=Louis&password=pass>

But this raises an exception :

io.ktor.features.CannotTransformContentToTypeException: Cannot transform this request's content to class io.ktor.http.Parameters

So I guess I should not give credentials to the server via POST body. I have tried sending credentials in JSON with ContentNegocition installed but I get a similar error. If someone could help me ... I will update the documentation once I know how it works.

Providing the parameters in the URL is passing them in the Query Parameters. You can’t send them through the URL if you are expecting them in the POST request body

Thanks, it works. I can't believe I lost a nearly full day on such a trivial error !😱

Also – there's a dedicated #ktor channel