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I'm starting to develop a simple PHP RESTful API. After reading some tutorials, one of the features about REST is that the

"... statelessness is key. Essentially, what this means is that the necessary state to handle the request is contained within the request itself, whether as part of the URI, query-string parameters, body, or headers"

Therefore, it means that my PHP server won't need to have $_SESSION ? What kind of approach do you recommend ? Using a token (valid for a short limit of time) in the URL doesn't seem a bit unsecure? For example www.myapi.com/1233asdd123/get_user/12.

Many thanks.

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If you're a web developer of any sort, you'll have heard this sentence probably 1,000 times: "HTTP is a stateless protocol". This means that every session works with a token exchanged between the server and the client.

When you use PHP's built-in sessions, the server is actually doing exactly that, even if you don't realize it: it generates a session_id and passes it to the client. The client passes the session_id token back normally on a cookie; PHP allows including the session token also on the URL, as a GET parameter, but I personally recommend disabling that feature (disabled by default on PHP 5.3+).

In your case, yes, you won't be using PHP's sessions.
You create a table in your database storing all session tokens and the associated session.

Tokens should have a short lifespan (for example, 30 minutes) and should be refreshed frequently. Refreshes are important not only to extend the life of the session (every refresh gives you an extra 30 minutes or so), but also help fighting against thefts of the session key. In some REST servers we created, the session token lives for 30 minutes and users are given a new token on the first request made after 10 minutes the session started. When clients are sent a new token, the old one is invalidated immediately.

You could pass the token to the server in any way, but adding it as a GET parameter is not an ideal solution for two reasons: 1. GET parameters are often written in the access logs of the servers and 2. users often copy/paste URLs and share them, and that can expose their session token.
For API servers, the best approach is to include the session token in one of the headers of the HTTP request. For example, you could set your Authorization header: Authorization: SessionToken 123123123 where 123123123 is your token and SessionToken is a string to tell the server to use your authorization method (you're free to choose your own name, as long as it's not one of the default methods like Basic; be consistent, though!).

Security on API servers is normally obtained by using SSL. Basically, if you have an API server, you must protect it with HTTPS (SSL).
There are methods to achieve security also without using SSL, but they require signing each request and are really complicate to implement and to use - and the overhead they add is probably bigger than the one of SSL.

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and if i build a mobile app, i can add that authorization header as easily ? thanks for the helpful comment
@DiogoMendonça Every library I've seen so far allowed you to add custom headers easily, on every platform. It's a pretty much standard thing! PS: this tool could be helpful for development: getpostman.com
sorry, just a question: is it better to send tokens with Nonce?
@DiogoMendonça I'm afraid that's a "wrong" question to ask! How would you use a nonce?
maybe in the Authorization Header send something like "AccessToken=2abx123vvae, Nonce=123133132". Just to increase security I guess :x
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A very common practice is to use a key value inside the URL:

www.myapi.com?key=ABCD1234

It is not less/more secure than POSTing the string. SSL encryption ensures that the whole payload cannot be intercepted by a man-in-the-middle.

More info :

You also mentioned a temporary access (session token). It is common in systems to log in using credentials (like the solution above) and obtain a temporary session token in the response. The session token is then used instead of the login details to query the service. It reduces the exposition of credentials in case of interception, and if someone manages to steal the session token, it will be working only for a few minutes. Good to have although not a necessity.

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