I'm working on a React application. I am defining user roles and restricting access to components based on the permissions level of the role. I am looking in to using signed cookies to set the permissions from a php backend. When I determine whether the application should render a component based on the data in the cookie, how do I verify that the roles in the cookie have not been redefined by the user without sending the cookie to the backend?
That's not the right approach, in my opinion. The components should be free to load - if there's something built-in to a component that an un-authenticated user shouldn't be able to see, there's nothing stopping someone from going into the source and discovering it themselves.
You have to take a different approach for front-end applications - all the components and UI are public. When the component fetches information from the server to display to the user, the server will still do the session authentication and respond with a 4xx (401 would be a good place to start) and the component would handle that response appropriately.
If modifying the role in the cookie would allow the user to gain more rights, then the solution is not to check the validity of the cookie on the client side. The user could also modify the client side script to circumvent/skip the integrity check of the cookies, and you would have the same problem as before.
The only correct solution is, that the user won't get those informations/scripts at the first place. So you need to check on the server side what informations are allowed to be send to the client, only send the data the user is allowed to see, and verify all actions the user sends to the server on the server side before you execute them.
Let me first start by saying that I realize that this is very similar to many other questions about service access control but I can't seem to find one response that is relevant on all of the points below, so I am asking (possibly) again.
Some background:
I am building a web application with .NET that is protected by a custom forms authentication implementation. This same app (within the same domain) needs to leverage several REST services related to data management from within JavaScript/jQuery as many of the app's functions are not well suited to post back use in the forms.
I am trying to determine the most secure way to implement access control for the REST service based on the authentication done server side when the app was first accessed.
Here is an example use case for what I am describing:
user logs into asp.net site using forms authentication and upon successful authentication the user is taken to the landing page of the application
the user chooses to access a page at ~/Users.aspx from a link on the landing page, which forms auth allows based on the cookie created by the authentication in step 1
users.aspx loads some basic HTML elements, like an empty table and a hidden field that contains a token (GUID) generated at page load. The token in the hidden field is used by JavaScript to access a REST service that retrieves data to populate the table. The token is stored in a database with a pre-defined expiration.
when the REST service is called with the token it is checked for expiration and used to determine the user making the call and provide authorization to the data being accessed from the database, if the user is authorized to access/update the data the service performs the requested service operation, extends the expiration on the token, and returns a response.
I know that the token would be visible to someone sniffing the request/response on the network unless SSL is used to encrypt the transmission, so SSL is used to counter this.
My question is:
Are there other attacks that the service would be vulnerable to?
is there a better way to handle authorization and user identification for the REST service based on the server side login other than a statically assigned token for the service? It seems to me that the statically assigned user token would be less secure since it would give endless access to the service if it were obtained by a malicious user.
assuming the answer to #2 is no, is there a better way to transmit the token to the client and store it there for the life of the page use knowing that it needs to be accessible from JavaScript/jQuery?
I'm currently implementing the Javascript Facebook login API.
Based on the callback response from Facebook, this client side script then sends a request with query string parameters to a URL on our site. Based on the email in that URL, the client is authenticated.
This is not secure. No other token that we can verify against is returned from Facebook (as far as I know), and we are expected to log the user in based on an email in a query string parameter, and no password.
I'd like to add another query string parameter that gives us some sort of assurance that the query string data came from a JavaScript redirect following the response from Facebook.
I'm thinking that this should be some sort of hashed value created by a client script that I can compare against server side. However, every resource used to create this secret key would be available to an attacker, via client cookies or through inspecting the client script.
Is there a common and secure approach to this problem that I can use?
Facebook apparently uses OAuth. Without getting into too much details (which you could find in relevant OAuth and FB documentation), OAuth operates with a secret shared between your server and the service provider (Facebook, in this instance), which is never revealed to the frontend Javascript, and is used to confirm if the callback you receive is genuine.
Pass Facebook a unique callback URL each time you authenticate user.
This URL should contain some security token, which, if present, will identify the authenticity of the logon attempt.
You can add a state variable to your requests to Facebook. This will be returned to you by Facebook to validate your request.
https://developers.facebook.com/docs/reference/dialogs/oauth/
02/20/2011:
It was confirmed by Facebook today that indeed there is one call in which the access_token is broadcast in the open . . . it just happens to be one call I use to make sure that the USER is still logged in before saving to my application database. Their recommendation was to use the SSL option provided as of last month for canvase and facebook as a whole. For the most part the Auth and Auth are secure.
Findings:
Subsequent to my posting there was a remark made that this was not really a question but I thought I did indeed postulate one. So that there is no ambiquity here is the question with a lead in:
Since there is no data sent from Facebook during the Canvas Load process that is not at some point divulged, including the access_token, session and other data that could uniquely identify a user, does any one see any other way other than adding one more layer, i.e., a password, sent over the wire via HTTPS along with the access_toekn, that will insure unique untampered with security by the user?
Using Wireshark I captured the local broadcast while loading my Canvas Application page. I was hugely surprised to see the access_token broadcast in the open, viewable for any one to see. This access_token is appended to any https call to the Facebook OpenGraph API.
Using facebook as a single click log on has now raised huge concerns for me. It is stored in a session object in memory and the cookie is cleared upon app termination and after reviewing the FB.Init calls I saw a lot of HTTPS calls so I assumed the access_token was always encrypted.
But last night I saw in the status bar a call from what was simply an http call that included the App ID so I felt I should sniff the Application Canvas load sequence.
Today I did sniff the broadcast and in the attached image you can see that there are http calls with the access_token being broadcast in the open and clear for anyone to gain access to.
Am I missing something, is what I am seeing and my interpretation really correct. If any one can sniff and get the access_token they can theorically make calls to the Graph API via https, even though the call back would still need to be the site established in Facebook's application set up.
But what is truly a security threat is anyone using the access_token for access to their own site. I do not see the value of a single sign on via Facebook if the only thing that was established as secure was the access_token - becuase for what I can see it clearly is not secure. Access tokens that never have an expire date do not change. Access_tokens are different for every user, to access to another site could be held tight to just a single user, but compromising even a single user's data is unacceptable.
http://www.creatingstory.com/images/InTheOpen.png
Went back and did more research on this:
FINDINGS:
Went back an re ran the canvas application to verify that it was not any of my code that was not broadcasting.
In this call: HTTP GET /connect.php/en_US/js/CacheData HTTP/1.1
The USER ID is clearly visible in the cookie. So USER_ID's are fully visible, but they are already. Anyone can go to pretty much any ones page and hover over the image and see the USER ID. So no big threat. APP_ID are also easily obtainable - but . . .
http://www.creatingstory.com/images/InTheOpen2.png
The above file clearly shows the FULL ACCESS TOKEN clearly in the OPEN via a Facebook initiated call.
Am I wrong. TELL ME I AM WRONG because I want to be wrong about this.
I have since reset my app secret so I am showing the real sniff of the Canvas Page being loaded.
Additional data 02/20/2011:
#ifaour - I appreciate the time you took to compile your response.
I am pretty familiar with the OAuth process and have a pretty solid understanding of the signed_request unpacking and utilization of the access_token. I perform a substantial amount of my processing on the server and my Facebook server side flows are all complete and function without any flaw that I know of. The application secret is secure and never passed to the front end application and is also changed regularly. I am being as fanatical about security as I can be, knowing there is so much I don’t know that could come back and bite me.
Two huge access_token issues:
The issues concern the possible utilization of the access_token from the USER AGENT (browser). During the FB.INIT() process of the Facebook JavaScript SDK, a cookie is created as well as an object in memory called a session object. This object, along with the cookie contain the access_token, session, a secret, and uid and status of the connection. The session object is structured such that is supports both the new OAuth and the legacy flows. With OAuth, the access_token and status are pretty much al that is used in the session object.
The first issue is that the access_token is used to make HTTPS calls to the GRAPH API. If you had the access_token, you could do this from any browser:
https://graph.facebook.com/220439?access_token=...
and it will return a ton of information about the user. So any one with the access token can gain access to a Facebook account. You can also make additional calls to any info the user has granted access to the application tied to the access_token. At first I thought that a call into the GRAPH had to have a Callback to the URL established in the App Setup, but I tested it as mentioned below and it will return info back right into the browser. Adding that callback feature would be a good idea I think, tightens things up a bit.
The second issue is utilization of some unique private secured data that identifies the user to the third party data base, i.e., like in my case, I would use a single sign on to populate user information into my database using this unique secured data item (i.e., access_token which contains the APP ID, the USER ID, and a hashed with secret sequence). None of this is a problem on the server side. You get a signed_request, you unpack it with secret, make HTTPS calls, get HTTPS responses back. When a user has information entered via the USER AGENT(browser) that must be stored via a POST, this unique secured data element would be sent via HTTPS such that they are validated prior to data base insertion.
However, If there is NO secured piece of unique data that is supplied via the single sign on process, then there is no way to guarantee unauthorized access. The access_token is the one piece of data that is utilized by Facebook to make the HTTPS calls into the GRAPH API. it is considered unique in regards to BOTH the USER and the APPLICATION and is initially secure via the signed_request packaging. If however, it is subsequently transmitted in the clear and if I can sniff the wire and obtain the access_token, then I can pretend to be the application and gain the information they have authorized the application to see. I tried the above example from a Safari and IE browser and it returned all of my information to me in the browser.
In conclusion, the access_token is part of the signed_request and that is how the application initially obtains it. After OAuth authentication and authorization, i.e., the USER has logged into Facebook and then runs your app, the access_token is stored as mentioned above and I have sniffed it such that I see it stored in a Cookie that is transmitted over the wire, resulting in there being NO UNIQUE SECURED IDENTIFIABLE piece of information that can be used to support interaction with the database, or in other words, unless there were one more piece of secure data sent along with the access_token to my database, i.e., a password, I would not be able to discern if it is a legitimate call. Luckily I utilized secure AJAX via POST and the call has to come from the same domain, but I am sure there is a way to hijack that.
I am totally open to any ideas on this topic on how to uniquely identify my USERS other than adding another layer (password) via this single sign on process or if someone would just share with me that I read and analyzed my data incorrectly and that the access_token is always secure over the wire.
Mahalo nui loa in advance.
I am not terribly familiar with Facebook's authentication/authorization methods, but I do believe that they implement oauth (or something close to it) for delegation, distributed authorization, and "single sign-on".
OAuth is described by RFC-5849
EDIT: Facebook Uses OAuth 2.0 which is still in working draft.
In OAuth, and similar systems, the "access_token" is only part of the picture. There is also typically a secret key, which is known only by the service provider (facebook) and the client application (your app). The secret key is the only part that is expected to stay secret - and that part is never sent over the wire (after it's initial issuance).
In the case of Facebook, I think the secret key is assigned to you when you register your application to use their API, and the 'access_token' is returned to you for a given user, whenever the user agrees to allow your app to access their info.
Messages are sent in the clear, including the user's username, and the relevant "access_token"; However, each message must also include a valid signature in order to be accepted by the server. The signature is a cryptographically computed string, that is created using a technique called HMAC.
Computing the HMAC signature requires both the token and the secret, and includes other key parts of the message as well. Each signature is unique for the given message contents; and each message uses a nonce to ensure that no two messages can ever be exactly identical.
When the server receives a signed message, it starts by extracting the access_token (clear-text), and determining which app the token was issued for. It then retrieves the matching secret from its own local database (the secret is not contained in the message). Finally, the server uses the clear-text message, the clear-text access_token, and the secret to compute the expected HMAC signature for the message. If the computed signature matches the signature on the received message, then the message must have been sent by someone who knows the same secret (i.e. your application).
Have a look at Section 3.1 of RFC-5849 for an OAuth specific example, and further elaboration on the details.
Incidentally, the same approach is used by Amazon to control access to S3 and EC2, as well as most other service providers that offer API access with long-term authorization. Suffice it to say - this approach is secure. It might be a little counter-intuitive at first, but it makes sense once you think it through.
Adding a few links and quotes from Facebook Documentation:
Facebook is indeed using the HMAC-SHA256 algorithm. Registration document (PHP Example reading signed_request section).
Always verify the signed_request:
If you are unable to validate the
signed_request because you can't embed
your application secret (e.g. in
javascript or a desktop application)
then you MUST only use one piece of
information from the payload, the
oauth_token.
The Authentication Document contains a lot of useful info about the different flows you may use to authenticate a user. Also read the Security Considerations section at the bottom of the page:
Cross site request forgery is an
attack in which an trusted
(authenticated and authorized) user
unknowingly performs an action on
website. To prevent this attack, you
should pass an identifier in the state
parameter, and then validate the state
parameter matches on the response. We
strongly recommend that any app
implementing Facebook user login
implement CSRF protection using this
mechanism.
It was confirmed by Facebook that indeed there is one call in which the access_token is broadcast in the open - it just happens to be one call I use to make sure that the user is still logged in before saving to my application database. Their recommendation was to use the SSL option provided as of last month for canvas and Facebook as a whole. For the most part the Auth and Auth are secure.
To ensure a secure interface between a third party application and a Facebook application or even any website that uses Facebook Single Sign on, an identity question would provide the extra layer when used in conjunction with the access_token.
Either that or require your users to use Facebook with the new SSL feature of Facebook and Facebook Canvas Applications. If the access_token is broadcast in the open it cannot be used to uniquely identify anyone in your third party database when needing to have a confirmed identity before database interactions.
We have a POST to a PL/SQL database procedure that (a) does some database operations based on the POST parameters and (b) redirects the user to a page showing the results.
The problem is, when the user does a browser "refresh" of the results page, that still has the original request, so it calls the database procedure and resends the parameters.
There are things we can do with saving state so bad things don't happen if the request gets sent in again. But that got me wondering.
Is there a way to tell the browser to set the url to the redirect call, not the original user request? This would probably be in either the redirect itself, or in Javascript on the target page.
You don't mention what you are using to serve the page, but make sure you perform an EXTERNAL redirect. Some platforms will internally redirect within a site.
For instance, with Apache HTTP Server, you need to specify the force-redirect flag in mod_rewrite: http://httpd.apache.org/docs/1.3/mod/mod_rewrite.html#RewriteRule
The 4th response here has a decent explanation of this as well.
The canonical solution is described pretty well on Wikipedia. See Post/Redirect/Get. You want the code that's handling the POST to redirect to a GET when it's work is done, as refreshing a GET will not resubmit form data.