REST is stateless and doesn’t maintain any states between the requests. Client cookies / headers are set to maintain the user state like authentication. Say Client username/password are validated by third part authentication mechanism – 2nd level OTP gerneation etc. Once user get authenticated – headers /cookies comes to rest service end point exposed and we can assume user as auth since user is coming with valid headers/cookies. Now certain info of user like IP is either maintained in the cache and after that if request is coming from same Ip (mac address) for listed resources User is allowed. And cache is maintained for some particular time which get invalidated once time lapses. So either cache can be used or DB entries can be used to persist info b/w the requests.

在开发RESTful服务时，为了登录，您需要对用户进行身份验证。一种可能的选择是在每次执行用户操作时发送用户名和密码。在这种情况下，服务器将根本不存储会话数据。

Another option is to generate a session-id on the server and send it to the client, so the client will be able to send session-id to the server and authenticate with that. This is much much safer than sending username and password each time, since if somebody gets their hand on that data, then he/she can impersonate the user until the username and password is changed. You may say that even the session id can be stolen and the user will be impersonated in that case and you are right. However, in this case impersonating the user will only be possible while the session id is valid.

如果RESTful API需要用户名和密码才能更改用户名和密码，那么即使有人使用会话id冒充用户，黑客也无法锁定真正的用户。

会话id可以通过单向锁定(加密)某个标识用户的东西并将时间添加到会话id中来生成，这样就可以定义会话的过期时间。

The server may or may not store session ids. Of course, if the server stores the session id, then it would violate the criteria defined in the question. However, it is only important to make sure that the session id can be validated for the given user, which does not necessitate storing the session id. Imagine a way that you have a one-way-encryption of email, user id and some user-specific private data, like favorite color, this would be the first level and somehow adding the username date to the encrypted string and apply a two-way encryption. As a result when a session id is received, the second level could be decrypted to be able to determine which username the user claims to be and whether the session time is right. If this is valid, then the first level of encryption could be validated by doing that encryption again and checking whether it matches the string. You do not need to store session data in order to achieve that.

您必须在客户端管理客户端会话。这意味着您必须在每个请求中发送身份验证数据，并且您可能(但不一定)在服务器上有一个内存缓存，它将身份验证数据与用户信息(如身份、权限等)配对。

这种REST无状态约束非常重要。如果不应用此约束，您的服务器端应用程序将不能很好地扩展，因为维护每个客户机会话将是它的阿喀琉斯之踵。

The whole concept is different... You don't need to manage sessions if you are trying to implement RESTFul protocol. In that case it is better to do authentication procedure on every request (whereas there is an extra cost to it in terms of performance - hashing password would be a good example. not a big deal...). If you use sessions - how can you distribute load across multiple servers? I bet RESTFul protocol is meant to eliminate sessions whatsoever - you don't really need them... That's why it is called "stateless". Sessions are only required when you cannot store anything other than Cookie on a client side after a reqest has been made (take old, non Javascript/HTML5-supporting browser as an example). In case of "full-featured" RESTFul client it is usually safe to store base64(login:password) on a client side (in memory) until the applictation is still loaded - the application is used to access to the only host and the cookie cannot be compromised by the third party scripts...

我强烈建议禁用RESTFul服务的cookie认证…检查Basic/Digest Auth -这对于基于rest的服务应该足够了。

我知道这里的基本问题是混淆了会议和国家。虽然REST指定不应该在服务器上存储状态，但没有什么可以阻止您存储用户会话。

管理服务器上的状态意味着您的服务器确切地知道客户机正在做什么(它们正在应用程序的哪个部分中查看哪个页面)。这是你不需要做的。

我同意其他人的说法，你应该保持会话存储的最小大小;虽然这是常识，但实际上也取决于应用程序。 因此，简而言之，您仍然可以保留一个带有缓存数据的会话，以较小的服务器负载处理请求，并通过提供一个临时身份验证/访问令牌供客户机使用来管理身份验证。每当会话/令牌过期时，生成一个新的会话/令牌，并要求客户端使用它。

有人可能会说，客户端应该更好地生成令牌。我说它是双向工作的，这取决于应用程序，以及谁将使用API。

在服务器上保留一些敏感的会话数据也是正确的做法。例如，您不能相信客户端会保留包含名为“isFreeGift”字段的购物车。这些信息应该保存在服务器上。

Santanu Dey在回答中提供的视频链接很有帮助。如果你还没看过，就看看吧。

只是一个旁注:似乎所有已经给出的答案都忽略了一个事实，即某些操作可能会导致服务器负载过重。这与功耗、硬件消耗和成本(对于按CPU周期租用的服务器)有关。一个优秀的开发人员不应该懒惰地优化他们的应用程序，即使操作可以在一些租用的服务器上的现代CPU上快速完成，而且他们不需要支付电费和维护费用。

虽然这个问题是几年前的事了，但我希望我的回答仍然会有帮助。

无状态和有状态的主要区别在于每次都将数据传递回服务器。在无状态的情况下，客户端必须提供所有的信息，所以很多参数可能需要在每个请求中传递。在有状态的情况下，cliet只传递一次这些参数，它们由服务器维护，直到客户端再次修改。

在我看来，API应该是无状态的，这允许快速扩展。