SecretAuthenticationProvider for Ktor 2.x

SecretAuthenticationProvider.kt

import io.ktor.serialization.*
import io.ktor.server.application.*
import io.ktor.server.auth.*
import io.ktor.server.request.*

class SecretAuthenticationProvider internal constructor(config: Config) : AuthenticationProvider(config) {

    internal val key: (ApplicationCall) -> String? = { call -> call.request.header("secret") }
    private val expectedKey: String = config.expectedKey ?: throw Exception("No key provided")

    class Config internal constructor(name: String?) : AuthenticationProvider.Config(name) {

        internal var expectedKey: String? = null

        internal fun build() = SecretAuthenticationProvider(this)
    }

    override suspend fun onAuthenticate(context: AuthenticationContext) {
        val secret = key(context.call)
        if (secret != expectedKey) {
            throw AuthenticationException()
        }
    }
}

fun AuthenticationConfig.secret(
    name: String? = null,
    configure: SecretAuthenticationProvider.Config.() -> Unit
) {
    val provider = SecretAuthenticationProvider.Config(name).apply(configure).build()
    register(provider)
}