接注册完成我们来完成用户登陆：邮箱作为账户

1. 注册路由：

SKUserController中添加function：   
 public func login(req: Request)throws-> EventLoopFuture<String>{
...
}

 router.get("login", use: SKUserController().login)

2. 用户登陆很常规会遇到几个常规问题：
   · 账户不存在
   . 账户存在密码不正确

public func login(req: Request)throws-> EventLoopFuture<String>{
        struct InnerUser: Content{
            var email: String
            var password: String
        }
        
        let user = try! req.query.decode(InnerUser.self)
     return   SKUser.query(on: req).group(SQLiteBinaryOperator.or) { (or) in
            or.filter(\.email, SQLiteBinaryOperator.equal, user.email)
            }.all().flatMap { (us) -> EventLoopFuture<String> in
                let result = req.eventLoop.newPromise(String.self)

                if us.isEmpty {
                    result.succeed(result: "用户不存在")
                    return result.futureResult
                }else{
                    
                    if us.first!.password.elementsEqual(user.password.md5Base64) {
                        
                        result.succeed(result: "登陆成功:\(us.first!)")
                    }else{
                        result.succeed(result: "密码错误")
                    }
                    return result.futureResult
                }
        }
        
    }