Is using sessions in a RESTful API really violating RESTfulness? I have seen many opinions going either direction, but I'm not convinced that sessions are RESTless. From my point of view:
authentication is not prohibited for RESTfulness (otherwise there'd be little use in RESTful services)
authentication is done by sending an authentication token in the request, usually the header
this authentication token needs to be obtained somehow and may be revoked, in which case it needs to be renewed
the authentication token needs to be validated by the server (otherwise it wouldn't be authentication)
So how do sessions violate this?
client-side, sessions are realized using cookies
cookies are simply an extra HTTP header
a session cookie can be obtained and revoked at any time
session cookies can have an infinite life time if need be
the session id (authentication token) is validated server-side
As such, to the client, a session cookie is exactly the same as any other HTTP header based authentication mechanism, except that it uses the Cookie header instead of the Authorization or some other proprietary header. If there was no session attached to the cookie value server-side, why would that make a difference? The server side implementation does not need to concern the client as long as the server behaves RESTful. As such, cookies by themselves should not make an API RESTless, and sessions are simply cookies to the client.
Are my assumptions wrong? What makes session cookies RESTless?
First of all, REST is not a religion and should not be approached as such. While there are advantages to RESTful services, you should only follow the tenets of REST as far as they make sense for your application.
That said, authentication and client side state do not violate REST principles. While REST requires that state transitions be stateless, this is referring to the server itself. At the heart, all of REST is about documents. The idea behind statelessness is that the SERVER is stateless, not the clients. Any client issuing an identical request (same headers, cookies, URI, etc) should be taken to the same place in the application. If the website stored the current location of the user and managed navigation by updating this server side navigation variable, then REST would be violated. Another client with identical request information would be taken to a different location depending on the server-side state.
Google's web services are a fantastic example of a RESTful system. They require an authentication header with the user's authentication key to be passed upon every request. This does violate REST principles slightly, because the server is tracking the state of the authentication key. The state of this key must be maintained and it has some sort of expiration date/time after which it no longer grants access. However, as I mentioned at the top of my post, sacrifices must be made to allow an application to actually work. That said, authentication tokens must be stored in a way that allows all possible clients to continue granting access during their valid times. If one server is managing the state of the authentication key to the point that another load balanced server cannot take over fulfilling requests based on that key, you have started to really violate the principles of REST. Google's services ensure that, at any time, you can take an authentication token you were using on your phone against load balance server A and hit load balance server B from your desktop and still have access to the system and be directed to the same resources if the requests were identical.
What it all boils down to is that you need to make sure your authentication tokens are validated against a backing store of some sort (database, cache, whatever) to ensure that you preserve as many of the REST properties as possible.
I hope all of that made sense. You should also check out the Constraints section of the wikipedia article on Representational State Transfer if you haven't already. It is particularly enlightening with regard to what the tenets of REST are actually arguing for and why.
First, let's define some terms:
RESTful:
One can characterise applications conforming to the REST constraints
described in this section as "RESTful".[15] If a service violates any
of the required constraints, it cannot be considered RESTful.
according to wikipedia.
stateless constraint:
We next add a constraint to the client-server interaction:
communication must be stateless in nature, as in the
client-stateless-server (CSS) style of Section 3.4.3 (Figure 5-3),
such that each request from client to server must contain all of the
information necessary to understand the request, and cannot take
advantage of any stored context on the server. Session state is
therefore kept entirely on the client.
according to the Fielding dissertation.
So server side sessions violate the stateless constraint of REST, and so RESTfulness either.
As such, to the client, a session cookie is exactly the same as any
other HTTP header based authentication mechanism, except that it uses
the Cookie header instead of the Authorization or some other
proprietary header.
By session cookies you store the client state on the server and so your request has a context. Let's try to add a load balancer and another service instance to your system. In this case you have to share the sessions between the service instances. It is hard to maintain and extend such a system, so it scales badly...
In my opinion there is nothing wrong with cookies. The cookie technology is a client side storing mechanism in where the stored data is attached automatically to cookie headers by every request. I don't know of a REST constraint which has problem with that kind of technology. So there is no problem with the technology itself, the problem is with its usage. Fielding wrote a sub-section about why he thinks HTTP cookies are bad.
From my point of view:
authentication is not prohibited for RESTfulness (otherwise there'd be little use in RESTful services)
authentication is done by sending an authentication token in the request, usually the header
this authentication token needs to be obtained somehow and may be revoked, in which case it needs to be renewed
the authentication token needs to be validated by the server (otherwise it wouldn't be authentication)
Your point of view was pretty solid. The only problem was with the concept of creating authentication token on the server. You don't need that part. What you need is storing username and password on the client and send it with every request. You don't need more to do this than HTTP basic auth and an encrypted connection:
Figure 1. - Stateless authentication by trusted clients
You probably need an in-memory auth cache on server side to make things faster, since you have to authenticate every request.
Now this works pretty well by trusted clients written by you, but what about 3rd party clients? They cannot have the username and password and all the permissions of the users. So you have to store separately what permissions a 3rd party client can have by a specific user. So the client developers can register they 3rd party clients, and get an unique API key and the users can allow 3rd party clients to access some part of their permissions. Like reading the name and email address, or listing their friends, etc... After allowing a 3rd party client the server will generate an access token. These access token can be used by the 3rd party client to access the permissions granted by the user, like so:
Figure 2. - Stateless authentication by 3rd party clients
So the 3rd party client can get the access token from a trusted client (or directly from the user). After that it can send a valid request with the API key and access token. This is the most basic 3rd party auth mechanism. You can read more about the implementation details in the documentation of every 3rd party auth system, e.g. OAuth. Of course this can be more complex and more secure, for example you can sign the details of every single request on server side and send the signature along with the request, and so on... The actual solution depends on your application's need.
Cookies are not for authentication. Why reinvent a wheel? HTTP has well-designed authentication mechanisms. If we use cookies, we fall into using HTTP as a transport protocol only, thus we need to create our own signaling system, for example, to tell users that they supplied wrong authentication (using HTTP 401 would be incorrect as we probably wouldn't supply Www-Authenticate to a client, as HTTP specs require :) ). It should also be noted that Set-Cookie is only a recommendation for client. Its contents may be or may not be saved (for example, if cookies are disabled), while Authorization header is sent automatically on every request.
Another point is that, to obtain an authorization cookie, you'll probably want to supply your credentials somewhere first? If so, then wouldn't it be RESTless? Simple example:
You try GET /a without cookie
You get an authorization request somehow
You go and authorize somehow like POST /auth
You get Set-Cookie
You try GET /a with cookie. But does GET /a behave idempotently in this case?
To sum this up, I believe that if we access some resource and we need to authenticate, then we must authenticate on that same resource, not anywhere else.
Actually, RESTfulness only applies to RESOURCES, as indicated by a Universal Resource Identifier. So to even talk about things like headers, cookies, etc. in regards to REST is not really appropriate. REST can work over any protocol, even though it happens to be routinely done over HTTP.
The main determiner is this: if you send a REST call, which is a URI, then once the call makes it successfully to the server, does that URI return the same content, assuming no transitions have been performed (PUT, POST, DELETE)? This test would exclude errors or authentication requests being returned, because in that case, the request has not yet made it to the server, meaning the servlet or application that will return the document corresponding to the given URI.
Likewise, in the case of a POST or PUT, can you send a given URI/payload, and regardless of how many times you send the message, it will always update the same data, so that subsequent GETs will return a consistent result?
REST is about the application data, not about the low-level information required to get that data transferred about.
In the following blog post, Roy Fielding gave a nice summary of the whole REST idea:
http://groups.yahoo.com/neo/groups/rest-discuss/conversations/topics/5841
"A RESTful system progresses from one steady-state to the
next, and each such steady-state is both a potential start-state
and a potential end-state. I.e., a RESTful system is an unknown
number of components obeying a simple set of rules such that they
are always either at REST or transitioning from one RESTful
state to another RESTful state. Each state can be completely
understood by the representation(s) it contains and the set of
transitions that it provides, with the transitions limited to a
uniform set of actions to be understandable. The system may be
a complex state diagram, but each user agent is only able to see
one state at a time (the current steady-state) and thus each
state is simple and can be analyzed independently. A user, OTOH,
is able to create their own transitions at any time (e.g., enter
a URL, select a bookmark, open an editor, etc.)."
Going to the issue of authentication, whether it is accomplished through cookies or headers, as long as the information isn't part of the URI and POST payload, it really has nothing to do with REST at all. So, in regards to being stateless, we are talking about the application data only.
For example, as the user enters data into a GUI screen, the client is keeping track of what fields have been entered, which have not, any required fields that are missing etc. This is all CLIENT CONTEXT, and should not be sent or tracked by the server. What does get sent to the server is the complete set of fields that need to be modified in the IDENTIFIED resource (by the URI), such that a transition occurs in that resource from one RESTful state to another.
So, the client keeps track of what the user is doing, and only sends logically complete state transitions to the server.
As I understand, there are two types of state when we are talking about sessions
Client and Server Interaction State
Resource State
Stateless constraint here refers to the second type in Rest. Using cookies (or local storage) does not violate Rest since it is related to the first.
Fielding says: 'Each request from client to server must contain all of the information necessary to understand the request, and cannot take advantage of any stored context on the server. Session state is therefore kept entirely on the client.'
The thing here is that every request to be fulfilled on the server needs the all necessary data from the client. Then this is considered as stateless. And again, we're not talking about cookies here, we're talking about resources.
HTTP transaction, basic access authentication, is not suitable for RBAC, because basic access authentication uses the encrypted username:password every time to identify, while what is needed in RBAC is the Role the user wants to use for a specific call.
RBAC does not validate permissions on username, but on roles.
You could tric around to concatenate like this: usernameRole:password, but this is bad practice, and it is also inefficient because when a user has more roles, the authentication engine would need to test all roles in concatenation, and that every call again. This would destroy one of the biggest technical advantages of RBAC, namely a very quick authorization-test.
So that problem cannot be solved using basic access authentication.
To solve this problem, session-maintaining is necessary, and that seems, according to some answers, in contradiction with REST.
That is what I like about the answer that REST should not be treated as a religion. In complex business cases, in healthcare, for example, RBAC is absolutely common and necessary. And it would be a pity if they would not be allowed to use REST because all REST-tools designers would treat REST as a religion.
For me there are not many ways to maintain a session over HTTP. One can use cookies, with a sessionId, or a header with a sessionId.
If someone has another idea I will be glad to hear it.
i think token must include all the needed information encoded inside it, which makes authentication by validating the token and decoding the info
https://www.oauth.com/oauth2-servers/access-tokens/self-encoded-access-tokens/
No, using sessions does not necessarily violate RESTfulness. If you adhere to the REST precepts and constraints, then using sessions - to maintain state - will simply be superfluous. After all, RESTfulness requires that the server not maintain state.
Sessions are not RESTless
Do you mean that REST service for http-use only or I got smth wrong? Cookie-based session must be used only for own(!) http-based services! (It could be a problem to work with cookie, e.g. from Mobile/Console/Desktop/etc.)
if you provide RESTful service for 3d party developers, never use cookie-based session, use tokens instead to avoid the problems with security.
Related
I am trying to understand statelessness in restful APIs in the context of authentication. Here's the scenario:
The user logs in.
The server verifies the username and the password, and generates an opaque access token. It caches some information related to this token - for example, the expiration time, the userId, whether this token was explicitly invalidated before it expired, etc.
The token is sent to the client, and the client sends it with every future request.
List item
Fielding's dissertation defines statelessness as:
"...such that each request from client to server must contain all of the information necessary to understand the request, and cannot take advantage of any stored context on the server. Session state is therefore kept entirely on the client."
In my example, the client is sending the token with every request, so the first condition is satisfied. However, my server has a context associated with this session that is stored in the sessions cache.
Does this make my application stateful?
If yes, then is it that true statelessness be achieved only if we are using JWTs? I am pondering upon this as JWTs are quite new, so how were architects building truly stateless services before they were invented?
That's right. If you you maintaining the session you are keeping the state in server which makes the application hard to scale. True stateless applications can be scaled out and any server should be able to handle the request.
JWT is popular way to avoid sessions and everything is encapsulated inside the token for any server to auth/Authorize the request and help us achieve stateless application, they come with their own challenges however OpenID connect is the new way for Auth/Authorization.
Before jwt to make application stateless we used to keep session in DB (or Shared Cache) , and any server would like to check the session would have to contact DB.
Hope that Helps!
Briefly: No, such usage of token does not make your application stateful.
Detailed: When we talk about stateless/stateful, we consider usually only the data that affect business logic. Business logic does not usually depend on authentication data. For example, a user sends a request that contains all data needed to place some order. Normally creating an order does not depend on when this user has logged in, on his user ID, etc.
Does using tokens for authentication break REST principles, which is supposed to be stateless.
I have an application which is required to be REST and I stored some tokens in a database. Each time a user wants to do an action, they should get a token (by sending a username and a password) and send it to the server with every request.
No they, don't.
A key aspect of something like the authentication header is the fact that it's orthogonal to the request itself. It's a property of the request in the same way that a Content-Type header is.
How Authentication is implemented on the back end is not germane to the discussion as long as results of the requests that submit the header are consistent. There's no reason the process of validating an authentication header can't be a stateless process in and of itself.
The presence and content of the Authentication can certainly impact what a client receives from a request, from a 403 Unauthorized response, to a limited amount of content based on whether the client is, perhaps, using an "admin" token vs. a non-privileged user.
It's also in contrast to a Cookie, which represent Session state (which is not RESTful). This is because the two headers serve different purposes and offer up different application semantics.
Authentication Tokens are a standard way of authenticating REST Clients.
Authentication token themselves do not beak REST principles as long as your API doesn't behave differently based on the Auth token passed to the API.
i.e. if 2 consumers place the same request with different auth token, and they are both allowed to perform that operation, the result should be the same.
You can find more info on REST API authentication here: https://dzone.com/articles/api-security-ways-to-authenticate-and-authorize
No it does not break the rule of being stateless.
Why?
Because the server is not maintaining any session w.r.t the client. It is just validating the token provided by client and returning results based on that.
If its client that has to maintain any data related to the session (which happens in case of tokens since they are sent with every request) then it is not breaking the REST principle, it is still stateless since the server is not maintaining the session or data related to the session.
Hope that helped.
It does break Rest principles because once the service generates a temporary token based on login credentials, the service is no longer stateless. The service has to check with itself if the token has expired yet (the token is part of the system state now), for each call made using that token.
One can't say the session at any point is independent of all the client's previous actions, because if they did not log in correctly, they could not even use the system.
But you should use logins and tokens, and break the Restfulness in this small way for security.
I am building a RESTful API with multiple servers and I want to know if it's okay to store the access token in a central database server and then, for every request, verify if this access token is valid by querying the database and then performing the action given.
If I use sessions for this job, will it become non RESTful? Like even if I store the session data in a database? It's been a confusing idea to me for so long.
REST is stateless
REST stands for Representational State Transfer and this architecture was defined by Roy Thomas Fielding in the chapter 5 of his dissertation.
Fielding defined a set of constraints for the REST architecture. One of these constraints is the stateless communication between client and server, defined as following (the highlights are not present in his dissertation):
5.1.3 Stateless
[...] each request from client to server must contain all of the information necessary to understand the request, and cannot take advantage of any stored context on the server. Session state is therefore kept entirely on the client. [...]
So, if you keep the session state on the server, you break the stateless constraint. Hence, it's not REST. In REST you won't have a session on the server and, consequently, you won't have session identifiers.
Each request must contain all data to be processed
Each request from client to server must contain all of the necessary information to be understood by the server. With it, you are not depending on any session context stored on the server.
When accessing protected resources that require authentication, for example, each request must contain all necessary data to be properly authenticated/authorized. It means the authentication will be performed for each request.
Have a look at this quote from the RFC 7235 regarding considerations for new authentication schemes:
5.1.2. Considerations for New Authentication Schemes
There are certain aspects of the HTTP Authentication Framework that
put constraints on how new authentication schemes can work:
HTTP authentication is presumed to be stateless: all of the
information necessary to authenticate a request MUST be provided
in the request, rather than be dependent on the server remembering
prior requests. [...]
And authentication data (credentials) should belong to the standard HTTP Authorization header. From the RFC 7235:
4.2. Authorization
The Authorization header field allows a user agent to authenticate
itself with an origin server -- usually, but not necessarily, after
receiving a 401 (Unauthorized) response. Its value consists of
credentials containing the authentication information of the user
agent for the realm of the resource being requested.
Authorization = credentials
[...]
Please note that the name of this HTTP header is unfortunate because it carries authentication data instead of authorization. Anyways, this is the standard header for sending credentials.
Token based authentication
When performing a token based authentication, the tokens are your credentials. In this approach, your hard credentials (username and password) are exchanged for a token that is sent in each request. Again, the authentication must be performed for every request, so you won't take advantage of any stored context on the server.
It's perfectly valid storing your tokens somewhere in your server. And it won't break the stateless constraint of the REST architecture.
Tokens
Basically, the tokens can be opaque (which reveals no details other than the value itself, like a random string) or can be self-contained (like JSON Web Token):
Random String: A token can be issued by generating a random string and persisting it to a database with an expiration date and with a user identifier associated to it.
JSON Web Token (JWT): Defined by the RFC 7519, it's a standard method for representing claims securely between two parties. JWT is a self-contained token and enables you to store a user identifier, an expiration date and whatever you want (but don't store passwords) in a payload, which is a JSON encoded as Base64. The payload can be read by the client and the integrity of the token can be easily checked by verifying its signature on the server. You won't need to persist JWT tokens if you don't need to track them. Althought, by persisting the tokens, you will have the possibility of invalidating and revoking the access of them. To find some great resources to work with JWT, have a look at http://jwt.io.
There are many databases where you can persist your tokens. Depending on your requirements, you can explore different solutions such as relational databases, key-value stores or document stores.
Your RESTful API would need to be stateless. Stateless means, that it should not rely on prior communication, like in the case of authentication and cookies set before the request in question.
That does not mean however that you can not cache some authentication token on the server side, provided, that a client could make a request without it. This all means, that if the client can fall back to standard HTTP authentication on every request, it should still be ok. The goal with this is to enable load balancing, distribution, and no (or limited) memory use on the server side for conversations.
Other than that, you don't really need to follow all the "rules" if you are not planning to use the benefits it provides. You can, if you want, implement it any way you want as long as the tradoffs are known.
Edit: found a previous discussion on the topic: Do sessions really violate RESTfulness?
So I have kind of an issue to understand why "tokens" have so much hype in the differents new web technologies for authentication.
I understand it's meant to improve the controls you can "lose" when using cookies and session. But a lot of people are talking about the fact that it sticks to the Restful "ideology" by allowing a client-server communication to be Stateless.
But... does it ? I mean, a stateless communication means that the server doesn't have to store any informations on the client for auth, and that requests are 100% independent from one to another.
In the case of tokens :
Server obviously needs to store those ( just as the client in most cases of applications if you want to keep token over restart) so, both client and server does have a states.
Client need to poll "/get token" in order to be able to request anything else, and the result of this request shut the result of any further requests in. So in other words, if I was designing a state diagram, my diagram would consist of more than one state.
So to me, tokens are nothing close to what we could call a "stateless" communication (which is a necessary condition for a architecture to be Restful).
By the way, I think HTTP credentials are closer to achieve a stateless communication, because basically, even if the server still have a state by storing the credentials, the auth+request process rely on only one single request, (as credentials are full part of the very first request of an HTTP "conversation").
One other point HTTP credentials hit better than tokens is the "Client/server roles" in Restful API. This point states that a RESTFul communication split client and server, meaning inter alia that the client doesn't have to deal with data storage. But in the case of token, they definitely needs to be stored, at least temporarily (and even more if (for example) you want the browser to keep the token after a restart by using cookies or localstorage). In contrast, HTTP cred can be filled in by the user at every request of a conversation making the client non-data-storing just as it should be in Restful representation.
Also I wanted to point out that according to Rest architecture, any information held by the client should on it's own be enough for the client to decide whether or not he should delete/modify it, which is not the case with 99% of tokens system that doesn't make the client store tokens' timeout date (where cookies does).
So in conclusion, a lot of people are blaming HTTP creds or session for violating the Restfulness of an architecture. But tokens systems doesn't solve the issue at all, does it ?
As noted in your comments, I am assuming you are referring to jwt.io.
Server obviously needs to store those ( just as the client in most
cases of applications if you want to keep token over restart) so, both
client and server does have a states.
There is no requirement for the server to store any state. Even the default example on jwt.io demonstrates this:
{
"sub": "1234567890",
"name": "John Doe",
"admin": true
}
Using the JSON Web Token this information is signed and stored on the client. The information cannot be changed without knowing the secret, so in this design it is considered secure provided a "strong enough" secret key is used.
This is why it can be considered stateless. As you mentioned, the client does need to store the token and therefore carries state. However, the server does not, meaning the implementation on the server side can be considered stateless.
I'm building a picture diary on web application google app engine using python. Users can sign up and post pictures to their diary.
Also, I'm trying to conform as much as I can to the REST architecture of doing things.
The authentication scheme is based like this for the web application:
1. Post username/password from the frontend
2. Backend sets up a cookie if authentication is successful
3. The rest of the AJAX calls made are authenticated using this cookie.
Is there any way to conform to REST without using cookies ?
Now, I'm also building an android application where users can sign in and post/view their picture diary. I need to expose the data from web application's datastore so I'll be building a webservice to fetch data from the datastore.
The authentication scheme for the android client:
OPTION a
1. Post username/password over https to the web service
2. Web service returns a unique authorization token (store the token in the username/pwd table on the datastore)
3. Request subsequent services by adding this token to the Request Header of the request
4. Server maps the token to the username/pwd table and returns data if token is found
5. Authorization token expires after a certain period of time
OPTION b
1. Set up a secret key on the client and server side
2. Use "username:hash of password and secret key" in the authorization header of every request
3. server generates the password by extracting the password from the hash value using the same hash algorithm ; if successful returns data
btw, I didn't wanna use basic authorization because of its security vulnerabilities.
Which is better ?
Are there other significantly better ways to accomplish what I'm trying to do ? Security is quite a concern for me btw.
I'd appreciate if anyone has any insight into this issue. thanks.
I've been doing some research myself as to what would be the best solution. I think the 2-legged oauth might work in my case as Leonm suggested.
In this case the server has to provide the client with a consumer key/secret which in my case is hardcoded in the app.
The steps now would be:
1. Generate a signature using the oauth_parameters(consumer_key, signature_method, timestamp), request url, request parameters, and the SECRET.
2. Include the signature, oauth parameters when making a request.
3. Server verifies the request by generating the signature again except in this case it uses the SECRET that corresponds to the key
I think this way I am pretty much confirming to the REST principles. The server is statless as I far I understand now.
What are the pros/cons on doing things this way?
If "security is a concern" then I would say that you'd be a lot better off using open standards and a library to achieve what you want. The main reason for this is that if you do it yourself, you're very likely to forget something; these standards have had a lot of eyes looking at them, looking for holes.
Your options include (in increasing level of complexity)
Basic authentication and HTTPS
Everything is encrypted, which makes it impossible to compress or look into, it increases the overhead somewhat, using more horsepower on the server, and more perhaps battery power on the client. Simple to implement, since it's well supported by libraries.
Digest authentication
Unencrypted messages pass the wire, but the authentication is securely managed in the Authorization headers. See the wikipedia entry for more information.
OAuth
See how Google is providing OAuth for installed applications. I believe it isn't what you're looking for, since you're not asking to share data between applications, just authenticating users.
Roll your own
If you want to roll your own, I suggest looking at e.g. how Google's (now deprecated ?) ClientLogin used to work.
Clients would GET a protected resource, and get a 401 with instructions to perform a GoogleLogin authentication, including a URI for where to perform the login itself
Clients (knowing how to do this) POST a request in a specific manner to that URI
The server responds with a specific response including a (long) token
The client can now perform GET requests to the protected resource with that token.
Statelessness
You cite REST, which dictates that requests should not specifically depend on prior interaction: "... each request from client to server must contain all of the information necessary to understand the request, and cannot take advantage of any stored context on the server." (fielding) This means that a server shouldn't store conversational context (like an authentication token) in a table.
One way of fixing this is by using any of the token based approaches (where the server tells the client about a token it should use for future requests) where the token is not a random number, but a message to the server itself. To protect yourself from client tampering, it can be signed, and if you're afraid of clients looking at it, you can encrypt it.
Edit: Although I'm not certain, it seems unlikely that Google has a table of all authentication tokens ever issued; The length of their tokens suggests that the token is some encrypted message proving that whoever holds this token actually provided real credentials in some realm at some time.
OAuth does exactly what you want to do in a standard way.
You could use a combination of HTTPS and HTTP Basic Auth. Both are existing standards and should be secure enough when used together.