When using the OAuth protocol, you need a secret string obtained from the service you want to delegate to. If you are doing this in a web app, you can simply store the secret in your data base or on the file system, but what is the best way to handle it in a mobile app (or a desktop app for that matter)?
Storing the string in the app is obviously not good, as someone could easily find it and abuse it.
Another approach would be to store it on your server, and have the app fetch it on every run, never storing it on the phone. This is almost as bad, because you have to include the URL in the app.
The only workable solution I can come up with is to first obtain the Access Token as normal (preferably using a web view inside the app), and then route all further communication through our server, which would append the secret to the request data and communicate with the provider. Then again, I'm a security noob, so I'd really like to hear some knowledgeable peoples' opinions on this. It doesn't seem to me that most apps are going to these lengths to guarantee security (for example, Facebook Connect seems to assume that you put the secret into a string right in your app).
Another thing: I don't believe the secret is involved in initially requesting the Access Token, so that could be done without involving our own server. Am I correct?
Yes, this is an issue with the OAuth design that we are facing ourselves. We opted to proxy all calls through our own server. OAuth wasn't entirely flushed out in respect of desktop apps. There is no prefect solution to the issue that I've found without changing OAuth.
If you think about it and ask the question why we have secrets, is mostly for provision and disabling apps. If our secret is compromised, then the provider can only really revoke the entire app. Since we have to embed our secret in the desktop app, we are sorta screwed.
The solution is to have a different secret for each desktop app. OAuth doesn't make this concept easy. One way is have the user go and create an secret on their own and enter the key on their own into your desktop app (some facebook apps did something similar for a long time, having the user go and create facebook to setup their custom quizes and crap). It's not a great experience for the user.
I'm working on proposal for a delegation system for OAuth. The concept is that using our own secret key we get from our provider, we could issue our own delegated secret to our own desktop clients (one for each desktop app basically) and then during the auth process we send that key over to the top level provider that calls back to us and re-validates with us. That way we can revoke on own secrets we issue to each desktop client. (Borrowing a lot of how this works from SSL). This entire system would be prefect for value-add webservices as well that pass on calls to a third party webservice.
The process could also be done without delegation verification callbacks if the top level provider provides an API to generate and revoke new delegated secrets. Facebook is doing something similar by allowing facebook apps to allow users to create sub-apps.
There are some talks about the issue online:
http://blog.atebits.com/2009/02/fixing-oauth/
http://groups.google.com/group/twitter-development-talk/browse_thread/thread/629b03475a3d78a1/de1071bf4b820c14#de1071bf4b820c14
Twitter and Yammer's solution is a authentication pin solution:
https://dev.twitter.com/oauth/pin-based
https://www.yammer.com/api_oauth_security_addendum.html
With OAUth 2.0, you can store the secret on the server. Use the server to acquire an access token that you then move to the app and you can make calls from the app to the resource directly.
With OAuth 1.0 (Twitter), the secret is required to make API calls. Proxying calls through the server is the only way to ensure the secret is not compromised.
Both require some mechanism that your server component knows it is your client calling it. This tends to be done on installation and using a platform specific mechanism to get an app id of some kind in the call to your server.
(I am the editor of the OAuth 2.0 spec)
One solution could be to hard code the OAuth secret into the code, but not as a plain string. Obfuscate it in some way - split it into segments, shift characters by an offset, rotate it - do any or all of these things. A cracker can analyse your byte code and find strings, but the obfuscation code might be hard to figure out.
It's not a foolproof solution, but a cheap one.
Depending on the value of the exploit, some genius crackers can go to greater lengths to find your secret code. You need to weigh the factors - cost of previously mentioned server side solution, incentive for crackers to spend more efforts on finding your secret code, and the complexity of the obfuscation you can implement.
Do not store the secret inside the application.
You need to have a server that can be accessed by the application over https (obviously) and you store the secret on it.
When someone want to login via your mobile/desktop application, your application will simply forward the request to the server that will then append the secret and send it to the service provider. Your server can then tell your application if it was successful or not.
Then if you need to get any sensitive information from the service (facebook, google, twitter, etc), the application ask your server and your server will give it to the application only if it is correctly connected.
There is not really any option except storing it on a server. Nothing on the client side is secure.
Note
That said, this will only protect you against malicious client but not client against malicious you and not client against other malicious clients (phising)...
OAuth is a much better protocol in browser than on desktop/mobile.
There is a new extension to the Authorization Code Grant Type called Proof Key for Code Exchange (PKCE). With it, you don't need a client secret.
PKCE (RFC 7636) is a technique to secure public clients that don't use
a client secret.
It is primarily used by native and mobile apps, but the technique can
be applied to any public client as well. It requires additional
support by the authorization server, so it is only supported on
certain providers.
from https://oauth.net/2/pkce/
For more information, you can read the full RFC 7636 or this short introduction.
Here's something to think about. Google offers two methods of OAuth... for web apps, where you register the domain and generate a unique key, and for installed apps where you use the key "anonymous".
Maybe I glossed over something in the reading, but it seems that sharing your webapp's unique key with an installed app is probably more secure than using "anonymous" in the official installed apps method.
With OAuth 2.0 you can simply use the client side flow to obtain an access token and use then this access token to authenticate all further requests. Then you don't need a secret at all.
A nice description of how to implement this can be found here: https://aaronparecki.com/articles/2012/07/29/1/oauth2-simplified#mobile-apps
I don't have a ton of experience with OAuth - but doesn't every request require not only the user's access token, but an application consumer key and secret as well? So, even if somebody steals a mobile device and tries to pull data off of it, they would need an application key and secret as well to be able to actually do anything.
I always thought the intention behind OAuth was so that every Tom, Dick, and Harry that had a mashup didn't have to store your Twitter credentials in the clear. I think it solves that problem pretty well despite it's limitations. Also, it wasn't really designed with the iPhone in mind.
I agree with Felixyz. OAuth whilst better than Basic Auth, still has a long way to go to be a good solution for mobile apps. I've been playing with using OAuth to authenticate a mobile phone app to a Google App Engine app. The fact that you can't reliably manage the consumer secret on the mobile device means that the default is to use the 'anonymous' access.
The Google App Engine OAuth implementation's browser authorization step takes you to a page where it contains text like:
"The site <some-site> is requesting access to your Google Account for the product(s) listed below"
YourApp(yourapp.appspot.com) - not affiliated with Google
etc
It takes <some-site> from the domain/host name used in the callback url that you supply which can be anything on the Android if you use a custom scheme to intercept the callback.
So if you use 'anonymous' access or your consumer secret is compromised, then anyone could write a consumer that fools the user into giving access to your gae app.
The Google OAuth authorization page also does contain lots of warnings which have 3 levels of severity depending on whether you're using 'anonymous', consumer secret, or public keys.
Pretty scary stuff for the average user who isn't technically savvy. I don't expect to have a high signup completion percentage with that kind of stuff in the way.
This blog post clarifies how consumer secret's don't really work with installed apps.
http://hueniverse.com/2009/02/should-twitter-discontinue-their-basic-auth-api/
Here I have answer the secure way to storing your oAuth information in mobile application
https://stackoverflow.com/a/17359809/998483
https://sites.google.com/site/greateindiaclub/mobil-apps/ios/securelystoringoauthkeysiniosapplication
Facebook doesn't implement OAuth strictly speaking (yet), but they have implemented a way for you not to embed your secret in your iPhone app: https://web.archive.org/web/20091223092924/http://wiki.developers.facebook.com/index.php/Session_Proxy
As for OAuth, yeah, the more I think about it, we are a bit stuffed. Maybe this will fix it.
None of these solutions prevent a determined hacker from sniffing packets sent from their mobile device (or emulator) to view the client secret in the http headers.
One solution could be to have a dynamic secret which is made up of a timestamp encrypted with a private 2-way encryption key & algorithm. The service then decrypts the secret and determines if the time stamp is +/- 5 minutes.
In this way, even if the secret is compromised, the hacker will only be able to use it for a maximum of 5 minutes.
I'm also trying to come up with a solution for mobile OAuth authentication, and storing secrets within the application bundle in general.
And a crazy idea just hit me: The simplest idea is to store the secret inside the binary, but obfuscated somehow, or, in other words, you store an encrypted secret. So, that means you've got to store a key to decrypt your secret, which seems to have taken us full circle. However, why not just use a key which is already in the OS, i.e. it's defined by the OS not by your application.
So, to clarify my idea is that you pick a string defined by the OS, it doesn't matter which one. Then encrypt your secret using this string as the key, and store that in your app. Then during runtime, decrypt the variable using the key, which is just an OS constant. Any hacker peeking into your binary will see an encrypted string, but no key.
Will that work?
As others have mentioned, there should be no real issue with storing the secret locally on the device.
On top of that, you can always rely on the UNIX-based security model of Android: only your application can access what you write to the file system. Just write the info to your app's default SharedPreferences object.
In order to obtain the secret, one would have to obtain root access to the Android phone.
I would like to secure my mobile app ( hybrid app, build with ionic framework). On backend site I use the play framework. I would implement the following case. The user of the app should authenticate to rest backend by email and password, if the credentials correct the backend generates an token return ok with the generate token to client, otherwise the backend return bad request. If the user would try to login with incorrect credentials more then 10 times the user would deactivated for 1 hour.
The mobile app would load json data from backend with ajax calls, on each call in header would set the field 'X-AUTH-TOKEN' and the generate token. The backend check the token and if the token is correct the client get data from server with status ok else the client get none data and the status unauthorized. If the user logged out the token would destroyed on server and client side. The token would not change as long as the user is logged in, in worst case the token would not changed over more than many days. I could implement, that on each call the date of last call can saved and if the last call is more than x days in past the server return unauthorized and destroy the token. So the user should logged in. Is the case secure enough, or should I implement more logic?
What you are describing is very similar, if not identical to the many, many implementations of OAuth2. For more information on these types of flows, including diagrams, check out how Google describes their OAuth2 processes here: https://developers.google.com/accounts/docs/OAuth2
I'm not familiar with the play framework but you should speak with framework experts to see if there is a well-tested, battle-hardened oauth2 implementation out there for the Play Framework. If so, you want to use that. You really don't want to (and shouldn't) roll your own implementation unless you know what you're doing and are willing to pay for people to pentest it. Really, please don't do this if unsure.
On the Ionic Framework / Angular / Cordova side, you've basically got it correct, but should always consider some basic security considerations:
My guess is that you'd use local storage to store the access token. In REST we don't have sessions like in a traditional web server scenario so we use the token in lieu of the session. Of course the downside is that local storage can easily be inspected to obtain the access key if someone had either root access on the device and was able to work their way into the app sandbox and knew exactly what api key to grab from local storage, but if someone has root or physical access to the device then you've got a bigger problem, so this isn't a design flaw per-say. To a certain extent, using this method you're relying upon the OS/browser's local storage sandbox to prevent other apps from accessing the local storage in your ionic app. This is a bet I would be willing to make, but you'll need to judge that based on your security vs usability needs.
What you should really be focusing on is protecting the token from people who may be listening on the wire (think coffee shop wifi). This means setting up your auth rest servers to use exclusively HTTPS (don't fail back to HTTP). This may have downsides, but will be worth it to protect your user's data. You also correctly identified using the token header. You should never pass auth tokens in anything but the header or POST data.
Generally speaking, what you are describing should be safe for use in a consumer level app. This assumes you don't unwittingly use any malicious third party code in your app. As always, you should be especially wary of third party code and only use code that you absolutely trust. Any code run from inside your app can access local storage in the Cordova/browser local storage sandbox and could theoretically export the api token for use in other software to access your api. With that said, you asked about authentication and not authorization. Keep in mind that your users need to only have access to do certain things in the app based on user-roles or some sort of ACL. This authorization outside the scope of this answer but you need to ensure that this is done on the server side and has rate limiting or soft-deletes for shared resources to prevent a malicious user from deleting everything.
Good luck with ionic and have fun.
I may not be going about this in the best way possible, but as a school project, I'm in a group where we are developing a system to handle checking in and checking out of dorm rooms and handling any charges that may arise because of damages to items in the room. We are digitizing the project and putting in on the web and writing a native iPhone app (part of the assignment, I'd rather just make it a universal web app, but oh well). For the iPhone app, we're putting together a web API but I'm having some doubts about our attempts to keep the API secure.
Our process right now is a call to the API to log in with a username and a password hash, if it was a successful login, an Authentication Token is generated and returned to the iPhone in XML along with various other data. Each subsequent request requires this AuthToken. A user can either sign out, or if there's inactivity for 20 minutes, the AuthToken is destroyed server side. But this leaves the API open for the "Pass The Hash" attack where anybody listening in on the request can get the password hash out of the query string. Anybody with Wireshark and a simple filter can wait for somebody to sign in when everybody would be moving into the dorms and be able to manipulate just about anything.
Every single request is susceptible to the Pass The Hash attack. When logging in, the username and password can be repeated later to obtain a different AuthToken. Not only that, any already generated AuthTokens could be used and the session extended without the real user knowing.
I have thought of the idea of tying the AuthToken to an IP address and rejecting requests that use a valid AuthToken from an alternate IP address, is this reliable or will the iPhone be jumping IP addresses when on the cell network instead of Wifi? I want to give any malicious users a hard time, but obviously not legitimate users.
The project is still in the early stages so now would be the time to make drastic changes to the API like this. Any tips on securing a web API would be awesome.
Your best bet would be to send everything over SSL. That will prevent anyone listening to the wire and sniffing either the password hash or the authentication token.
You should also consider sending a nonce to the client that gets hashed along with the password to prevent replay attacks.
It's also pretty easy to change the authentication token on each request. This prevents both replay and session-fixation. Just make sure the tokens are good random numbers.
You need to use HTTPS.
Most anything on HTTP is susceptible if you include people using Wireshark. HTTPS encrypts all traffic between the client and the server and will prevent most packet sniffing attacks.
I'm working on a Windows Phone 7 application, and to go with it I will need a web service to send out live tile push notifications. I will save the clients URI channel in a database and every hour or so I will send out the correct live tile to all the subscribed clients. I will not be sending out any sensitive data to the clients, nor do the clients send any data to the service save for their channel URI, and I've made sure to protect the database against any sql-injections.
The exposed methods are for registering and unregistering a client, as well as sending the correct live tile to a client that requests it.
Given this information, does anyone have any recommendations on how I should secure the service, or is security even needed to begin with in this case?
Thanks!
EDIT:
Thanks for the answers! My peers decided to not use any security at all though, other than purging faulty requests from the database, since the scope of the application is quite limited and no sensitive data is being transmitted. Let's hope it won't bite us in our behinds later on, eh!
Unfortunately the best solution to this problem (at the moment) is to generate a hash in your app and use that to verify the data is really coming from your app. Obviously you'll need to obfuscate tyour code if doing this.
This is the best you can do without any authentication against the backend.
If you can, have the users register and authenticate with the backend and then tie this authentication token to the ANID of the device and do everything over SSL.
Unfortunately, currenlty, security of services and prevention of spoffed requests is quite tricky with WP7 without requiring a login to the backend.
Make sure you secure your channel to your backend service with SSL. This way the data you send to the server such as a the ChannelUri will be secure.
Building a hash into your application isnt security. People could get your XAP and decompile it to get the hash.
IMHO you are better to ensure your ChannelUri (unique to your app and not "stored" in your XAP anywhere) is secured when you send it.
On the backend just make sure you purge records that fail when you try and send it a tile notification. This will get rid of any records entered by non-phone parties.
Bottom line is that you need a login infrastructure with your backend to properly ensure only valid users are using your service.
I'm currently thinking how I could protect my REST API which is used only by my mobile application from being used by other applications?
Could a API-Key be a good solution, because just me know the secret API key.
Is there a better solution?
Leon, you keep mentioning "someone else using my API with another application". So, you want to tie your API to be used only by one application? So, you don't want to give access rights to a user, you want to give them instead to an instance of your application running on the user's mobile device.
In essence: You don't trust the user!
Well, in that case you need to make sure your application is closed source, need to code your credentials into your application in such a way that nobody can retrieve them or store the credentials for it in a specially encrypted manner on the device, the decryption key for it being readable only by your application. In a way, you need to implement a form of DRM to prevent people from doing stuff with data on their mobile device. And you need to hope that nobody can reverse engineer it.
If your app becomes popular / interesting enough, count on the fact that people who are very, very good at this sort of thing will look at your application and will break your encryption before you know it. Maybe, if you put the same amount of effort into it as Skype has, maybe then you can ward them off for a while.
But ask yourself: Why bother? Why don't I trust my users? Is it really worth it to jump through hoops like this to prevent some other application from using my API?
Just lead your user through a registration process in which each app instance gets a unique key from the server (or a unique HTTP auth password) and stores that somewhere on the user's mobile device. Then, to access the interesting features in the API, require the presence of this key/password. But don't go through extreme length to obfuscate or encrypt the key when you store it locally, it's not worth it. If you every detect misuse later, you can always revoke the access rights for a particular account on the server anyway.
Use HTTP Authentication. REST is all about using the facilities available in HTTP, so the native HTTP auth should be used. With basic authentication you’ll have to use HTTPS though. If you cannot do that use HTTP digest auth or NTLM.
All of them have different strengths and weaknesses, and not every one of them might be supported by your HTTP server and client library.