不变构造函数注入Kotlin类的正确方法

用Spring + Kotlin声明不可变的构造函数注入类的正确方法是什么？目前我有：

@RestController
public class AuthorizationController
{
    @Inject
    lateinit var facebookAuth: FacebookAuthorizationService //Mutable?

    @RequestMapping("/authorization")
    public fun authorization(@RequestParam(value = "network-type", defaultValue = "Facebook") name: String,
                             @RequestParam(value = "oauth-token") oauthToken: String,
                             @RequestParam(value = "oauth-token-secret",
                                     required = false) oauthTokenSecret: String?): Authorization
    {
        //TODO: Handle other network types
        return facebookAuth.authorization(oauthToken)
    }
}

我希望facebookAuth属性是不可变的。