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Consider an API that a client accesses directly (machine to machine) and that doesn't require user-specific authentication. The way I understand it, in client_credentials, the client must store a client_id and client_secret that it uses to acquire and refresh tokens. With an API key, the client just stores the key. What makes OAuth more secure in this case? It would appear to me that if the API key is never compromised, no attacker could pose as the intended client. And if the API key is compromised, it is effectively the same as compromising the client_id and client_secret, which an attacker would be able to use to obtain tokens and access the data in the API, posing as the client.
edit: clarified this is a machine-to-machine call
TLDR;
The difference comes down to direct access vs. delegated access.
OAuth allows you to make delegated access. The benefits of delegated access don't change if there is a user involved or not. The same arguments that make the OAuth Authorization code flow attractive for user-to-machine access, apply to the OAuth Client credentials flow for machine-to-machine access.
Ask yourself, do you want the resource server to handle client credentials or not?
On confidential clients for machine-to-machine access, the cost of delegated access vs. direct access may very well outweigh the benefits. That's why so many APIs still use API keys. You'll have to decide that for your individual use case.
Differences
In the OAuth client credentials flow, the client sends an access token to the resource server, which it got beforehand by the authorization server after presenting its client ID and secret. The resource server never sees the client secret. With an API key, the client sends the key with every request.
OAuth adds an additional layer of indirection with the authorization server, such that the credentials themselves never get transmitted to the resource server. This allows the authorization server to give the client only access for a limited amount of time or with limited permissions, without ever needing to change the actual client credentials. It also allows to revoke access tokens without revoking the credentials themselves. For multiple instances of a client this allows you to revoke access for some but not all.
Of course this all comes at the cost of a more complex implementation, and an additional roundtrip from the client to the authorization server.
I won't touch on transmission (URL, header, body, etc.) or format (random string, signed JWT, etc.), since these can be the same for access tokens just as for API keys.
Another, maybe not so obvious, advantage of OAuth is having a clear spec that libraries, documentation and discussions can be based on. With direct access there is no single best practice and different people may understand different things when referring to direct access methods like API keys.
With client credential flow your Client Id and Client Secret are sent to the authorization server to get back an access token. For all subsequent request to the API/resource servers, you pass the access token and not the client credentials themselves. The access token is usually a JWT, which is a set of encoded claims including the token expiry (exp), not before (nbf), token issuer (iss), authorized party (azp), roles, permissions, etc.
This has a number of advantages over a simple API Key approach. e.g.
If the access token (which is included in requests to the API/resource server) is compromised, it's only valid until it expires (which is typically ~1 day for M2M tokens). If an API Key is compromised, it can be used indefinitely or until it's explicitly blocked by the API/resource server.
JWT access tokens are encoded JSON objects that contains a number of fields (a.k.a. claims) that can be used for fine grained authorization e.g. roles, permissions, grant type, authorized party etc. An API Key is generally opaque and is all or nothing when it comes to auth.
You machine tokens can get validated and authorized on the API/resource servers the same way as your user tokens, so you don't end up with multiple auth implementations on the back-end.
OAuth Client Credentials Flow
What is the security difference between API Keys and the client credentials flow of OAuth?
OAuth client credentials flow is not meant to be used by public clients, just between machines.
From auth0.com/docs:
Client Credentials Flow
With machine-to-machine (M2M) applications, such as CLIs, daemons, or services running on your back-end, the system authenticates and authorizes the app rather than a user. For this scenario, typical authentication schemes like username + password or social logins don't make sense. Instead, M2M apps use the Client Credentials Flow (defined in OAuth 2.0 RFC 6749, section 4.4), in which they pass along their Client ID and Client Secret to authenticate themselves and get a token.
So, I am not sure what is your scenario, but I will assume in my reply that you are referring to public clients.
If it is in the public client code, then it is public
The way I understand it, in client_credentials, the client must store a client_id and client_secret that it uses to acquire and refresh tokens.
Yes, it needs to be stored in the client code for the client to be able to obtain the OAuth token.
If you use the client_secret from a web app or mobile app you are making it public, therefore not a secret anymore.
Extracting secrets from public clients
For example, in a web app all it takes to extract the client_secret is to hit F12 in the browser and search for it, thus how much time can this take?
Now, in a mobile app, some may think it's secure because they are compiled into a binary but is almost as easy as it is in the browser, because we have several open-source tools that can help us with this task, like the MobSF framework, and on Linux, you can even achieve this with the strings command. Using the MobSF to perform static binary analysis on the mobile app binary allows for anyone without hacking knowledge to easily extract the client_secret in minutes, just like I show in my article How to Extract an API key from a Mobile App with Static Binary Analysis:
The range of open source tools available for reverse engineering is huge, and we really can't scratch the surface of this topic in this article, but instead, we will focus in using the Mobile Security Framework(MobSF) to demonstrate how to reverse engineer the APK of our mobile app. MobSF is a collection of open-source tools that present their results in an attractive dashboard, but the same tools used under the hood within MobSF and elsewhere can be used individually to achieve the same results.
So, the process of extracting the api-key in my article is the same you will use to extract the client_secret or any other string of your interest in the mobile app binary.
OAuth or API Key?
What makes OAuth more secure in this case? It would appear to me that if the API key is never compromised, no attacker could pose as the intended client. And if the API key is compromised, it is effectively the same as compromising the client_id and client_secret, which an attacker would be able to use to obtain tokens and access the data in the API, posing as the client.
If used from a public client neither are secure, because if read my linked article, you understand by now how easy is to bypass an API Key or extract the client_secret and client_id.
So, if your client is public you should not use the OAuth client credential flow, thus you need to go with the insecure API key approach or you can be more diligent and try to apply defence-in-depth approaches, but this will depend if the API clients are only web apps or mobile apps or both.
If your API clients are only web apps I invite you to read my answer to the question Secure API data from calls out of the app, especially the section dedicated to Defending the API Server.
In the case the API clients are only mobile apps then I recommend you to read this answer I gave to the question How to secure an API REST for mobile app?, especially the sections Securing the API Server and A Possible Better Solution.
On the other hand, if your API clients are both a web app and a mobile app I recommend you to apply the security measures more relevant to you from both answers linked above.
Remember that security is always about adding as many layers of defences as you can afford or it's required by law. Even in the past century, the castles were built with a lot of different security defence layers, thus this is nothing new to the digital era.
Do You Want To Go The Extra Mile?
In any response to a security question I always like to reference the excellent work from the OWASP foundation.
For APIS
OWASP API Security Top 10
The OWASP API Security Project seeks to provide value to software developers and security assessors by underscoring the potential risks in insecure APIs, and illustrating how these risks may be mitigated. In order to facilitate this goal, the OWASP API Security Project will create and maintain a Top 10 API Security Risks document, as well as a documentation portal for best practices when creating or assessing APIs.
For Mobile Apps
OWASP Mobile Security Project - Top 10 risks
The OWASP Mobile Security Project is a centralized resource intended to give developers and security teams the resources they need to build and maintain secure mobile applications. Through the project, our goal is to classify mobile security risks and provide developmental controls to reduce their impact or likelihood of exploitation.
OWASP - Mobile Security Testing Guide:
The Mobile Security Testing Guide (MSTG) is a comprehensive manual for mobile app security development, testing and reverse engineering.
For Web Apps
The Web Security Testing Guide:
The OWASP Web Security Testing Guide includes a "best practice" penetration testing framework which users can implement in their own organizations and a "low level" penetration testing guide that describes techniques for testing most common web application and web service security issues.
I am using the Goodreads api to get book data for my react native app. I have to use a key for using the api. Is it OK for me to store the api key on the app itself or should I put the key on a server that redirects all the data to the app?
Is it OK for me to store the api key on the app itself
No, because as I demonstrate in the article How to Extract an API Key from a Mobile App by Static binary analysis it can be extracted with the help of several open source tools, like by using the Mobile Security Framework, but you can also grab the API key with a MitM attack, as I show in the article Steal that API Key with a Man in the Middle Attack, that uses the open source tool MiTM Proxy.
If you leave a third party API key in the mobile app, then they are up for grabs from attackers, and when they start using it without your knowledge your bill in the third party provider may go through the roof before you acknowledge that something is wrong, and on that time the only solution is to revoke the API key, thus shutting down the use of the mobile app, and if you make a new release of your mobile app with a new API key it will be just a matter of hours until the attacker come back and steal the API key again.
or should I put the key on a server that redirects all the data to the app?
Yes, and this is a good approach, because now you have only one place to store and protect all third part API keys. This have the benefit to let you control and throttle the use of them as you see fit.
With this solution you still need an API key in your mobile app to allow access to your API server, but while you continue vulnerable for attackers to steal it, you are now in direct control of throttling the access to your API server and if you identify in each access the WHO and the WHAT is accessing the API server, then you have a more fine grade control, but attacker will continue to be able to slip between all our defenses, because is very hard to know WHAT is accessing the API server.
You may be thinking by now... do you mind to explain the WHO vs the WHAT?
The Difference Between WHO and WHAT is Accessing the API Server
To better understand the differences between the WHO and the WHAT are accessing an API server, let’s use this picture:
The Intended Communication Channel represents the mobile app being used as you expected, by a legit user without any malicious intentions, using an untampered version of the mobile app, and communicating directly with the API server without being man in the middle attacked.
The actual channel may represent several different scenarios, like a legit user with malicious intentions that may be using a repackaged version of the mobile app, a hacker using the genuine version of the mobile app, while man in the middle attacking it, to understand how the communication between the mobile app and the API server is being done in order to be able to automate attacks against your API. Many other scenarios are possible, but we will not enumerate each one here.
I hope that by now you may already have a clue why the WHO and the WHAT are not the same, but if not it will become clear in a moment.
The WHO is the user of the mobile app that we can authenticate, authorize and identify in several ways, like using OpenID Connect or OAUTH2 flows.
OAUTH
Generally, OAuth provides to clients a "secure delegated access" to server resources on behalf of a resource owner. It specifies a process for resource owners to authorize third-party access to their server resources without sharing their credentials. Designed specifically to work with Hypertext Transfer Protocol (HTTP), OAuth essentially allows access tokens to be issued to third-party clients by an authorization server, with the approval of the resource owner. The third party then uses the access token to access the protected resources hosted by the resource server.
OpenID Connect
OpenID Connect 1.0 is a simple identity layer on top of the OAuth 2.0 protocol. It allows Clients to verify the identity of the End-User based on the authentication performed by an Authorization Server, as well as to obtain basic profile information about the End-User in an interoperable and REST-like manner.
While user authentication may let the API server know WHO is using the API, it cannot guarantee that the requests have originated from WHAT you expect, the original version of the mobile app.
Now we need a way to identify WHAT is calling the API server, and here things become more tricky than most developers may think. The WHAT is the thing making the request to the API server. Is it really a genuine instance of the mobile app, or is a bot, an automated script or an attacker manually poking around with the API server, using a tool like Postman?
For your surprise you may end up discovering that It can be one of the legit users using a repackaged version of the mobile app or an automated script that is trying to gamify and take advantage of the service provided by the application.
Well, to identify the WHAT, developers tend to resort to an API key that usually they hard-code in the code of their mobile app. Some developers go the extra mile and compute the key at run-time in the mobile app, thus it becomes a runtime secret as opposed to the former approach when a static secret is embedded in the code.
The above write-up was extracted from an article I wrote, entitled WHY DOES YOUR MOBILE APP NEED AN API KEY?, and that you can read in full here, that is the first article in a series of articles about API keys.
Your problem is not solved yet
Now that you know the difference between WHO and WHAT is accessing your API server you must have realized that your API server is still vulnerable to be abused by attackers.
You can resort now to employ several layers of defense, starting with reCaptcha V3, followed by Web Application Firewall(WAF) and finally if you can afford it a User Behavior Analytics(UBA) solution.
Google reCAPTCHA V3:
reCAPTCHA is a free service that protects your website from spam and abuse. reCAPTCHA uses an advanced risk analysis engine and adaptive challenges to keep automated software from engaging in abusive activities on your site. It does this while letting your valid users pass through with ease.
...helps you detect abusive traffic on your website without any user friction. It returns a score based on the interactions with your website and provides you more flexibility to take appropriate actions.
WAF - Web Application Firewall:
A web application firewall (or WAF) filters, monitors, and blocks HTTP traffic to and from a web application. A WAF is differentiated from a regular firewall in that a WAF is able to filter the content of specific web applications while regular firewalls serve as a safety gate between servers. By inspecting HTTP traffic, it can prevent attacks stemming from web application security flaws, such as SQL injection, cross-site scripting (XSS), file inclusion, and security misconfigurations.
UBA - User Behavior Analytics:
User behavior analytics (UBA) as defined by Gartner is a cybersecurity process about detection of insider threats, targeted attacks, and financial fraud. UBA solutions look at patterns of human behavior, and then apply algorithms and statistical analysis to detect meaningful anomalies from those patterns—anomalies that indicate potential threats. Instead of tracking devices or security events, UBA tracks a system's users. Big data platforms like Apache Hadoop are increasing UBA functionality by allowing them to analyze petabytes worth of data to detect insider threats and advanced persistent threats.
All this solutions work based on a negative identification model, by other words they try their best to differentiate the bad from the good by identifying what is bad, not what is good, thus they are prone to false positives, despite of the advanced technology used by some of them, like machine learning and artificial intelligence.
So you may find yourself more often than not in having to relax how you block the access to the API server in order to not affect the good users. This also means that this solutions require constant monitoring to validate that the false positives are not blocking your legit users and that at same time they are properly keeping at bay the unauthorized ones.
Regarding APIs serving mobile apps a positive identification model can be used by using a Mobile App Attestation solution that guarantees to the API server that the requests can be trusted without the possibility of false positives.
Mobile App Attestation
Use a Mobile App Attestation solution to enable the API server to know is receiving only requests from a genuine mobile app.
The role of a Mobile App Attestation service is to guarantee at run-time that your mobile app was not tampered or is not running in a rooted device by running a SDK in the background that will communicate with a service running in the cloud to attest the integrity of the mobile app and device is running on.
On successful attestation of the mobile app integrity a short time lived JWT token is issued and signed with a secret that only the API server and the Mobile App Attestation service in the cloud are aware. In the case of failure on the mobile app attestation the JWT token is signed with a secret that the API server does not know.
Now the App must sent with every API call the JWT token in the headers of the request. This will allow the API server to only serve requests when it can verify the signature and expiration time in the JWT token and refuse them when it fails the verification.
Once the secret used by the Mobile App Attestation service is not known by the mobile app, is not possible to reverse engineer it at run-time even when the App is tampered, running in a rooted device or communicating over a connection that is being the target of a Man in the Middle Attack.
The Mobile App Attestation service already exists as a SAAS solution at Approov(I work here) that provides SDKs for several platforms, including iOS, Android, React Native and others. The integration will also need a small check in the API server code to verify the JWT token issued by the cloud service. This check is necessary for the API server to be able to decide what requests to serve and what ones to deny.
Summary
Anything that runs on the client side and needs some secret to access an API can be abused in different ways and you must delegate the access to all third part APIs to a backend under your control, so that you reduce the attack surface, and at the same time protect their secrets from public pry eyes.
In the end, the solution to use in order to protect your API server must be chosen in accordance with the value of what you are trying to protect and the legal requirements for that type of data, like the GDPR regulations in Europe.
For react native use react-native-config library. While using this library you can secure your api keys as well as you can save more secret keys which use in the native code. Like we can save onesignal, codepush etc keys.
https://github.com/luggit/react-native-config
Store them in a .env file like this API_KEY=yourKey.
Install npm package react-native-dotenv.
Then import to to files as needed with react-native-dotenv package;
import { API_KEY } from 'react-native-dotenv'
The .env file should never be committed to Github.
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.
Is it possible to identify (authenticate) a mobile application HTTP request ?
for example a request from a web server can by identified by the domain or IP, assuming I know from where it should come from I can accept the request or deny if it came from an unexpected origin.
doe's mobile application has some sort of unique id (that cannot be mimicked)?
If you need to make secure HTTP calls (webservice API) from a mobile app (a native compiled app), you can try the following approach:
Edit: This approach assumes that you can't rely on the user operating the app for authentication purposes (because then you could simply ask the user to type in a secure password in the app).
Assuming you are implementing the app, save some sort of secret API key in the code.
When the app makes an API call via HTTP, it will always be done using HTTPS (so everything is encrypted).
The app will send the secret API key as a URL parameter.
The server will authenticate by checking if the secret key is correct.
Sniffing the app traffic will not reveal the secret key (because of the HTTPS).
You are mostly vulnerable to someone reverse-engineering your app to discover the secret key inside. This can be made tough by using various obfuscation and anti-debugging techniques, but cannot be made truly impossible. As long as you're using a compiled language (like Objective-C, not JS for a web-app) this will already be tough without any special games. If you avoid placing your API key string as-is and compute it using some short code in the app, you've made it about 1000 times tougher to discover.
Without knowing more about your specific problem, it's hard to suggest alternate approaches. Please give more details if you are looking for something different.
There are two methods used in practice. HTTP basic authentication (not much secure for mobile apps) and OAuth2 (secured compared to HTTP basic authentication).
HTTP Basic Authentication: The process is simple for both technical writers of API services, and also developers using them:
A developer is given an API key (typically an ID and Secret). This API key usually looks something like this: 3bb743bbd45d4eb8ae31e16b9f83c9ba:ffb7d6369eb84580ad2e52ca3fc06c9d.
He is responsible for storing API key in a secure place on their server, so that no one can access it. He makes API requests to the API service by feeding the API key in the HTTP Authorization header along with the word 'Basic' (which is used by the API server to properly decode the authorization credentials). The key is also Base64 encoded.
For example key could be: 3bb743bbd45d4eb8ae31e16b9f83c9ba:ffb7d6369eb84580ad2e52ca3fc06c9d
encoded in base64: M2JiNzQzYmJkNDVkNGViOGFlMzFlMTZiOWY4M2M5YmE6ZmZiN2Q2MzY5ZWI4NDU4MGFkMmU1MmNhM2ZjMDZjOWQ=.
The API server reverses this process. When it finds the HTTP Authorization header, it will decode base64 result, read the API key ID and Secret and validate these tokens before allowing the request to be processed.
HTTP Basic Authentication is simple but for mobile apps securing the API Key is a main concern. HTTP Basic Authentication requires raw API keys to be sent over the wire for each request, thereby increasing chances of misuse in the long run.
Also it is impractical as you cannot safely embed API keys into a mobile app that is distributed to many users.
For instance, if you build a mobile app with your API keys embedded inside of it, a user could reverse engineer your app, exposing this API key, and abusing your service.
So HTTP Basic Authentication risky in open environments, like web browsers and mobile applications.
NOTE: Like all authentication protocols, HTTP Basic Authentication must be used over SSL at all times.
OAuth2 for Mobile API Security:
OAuth2 is an excellent protocol for securing API services from open devices, and provides a better way to authenticate mobile users via token authentication.
OAuth2 token authentication works from a user perspective (OAuth2 name it password grant flow):
When a user starts the mobile app he is prompted for username or email and password.
The developer sends a POST request from app to API service with the login data included (over SSL). Then validate the user credentials, and create access token for the user which expires after a certain amount of time. This access token can be stored on mobile device, treating it like an API key which allows access to API service. When the access token expires user is prompted again for login details.
OAuth2 generates access tokens that can be stored in an open environment temporarily and are secure. It is secure because the access token are generated for temporary purpose and it reduces damage potential.
The token is stored according to the mobile platform used. For Android app, access tokens can be stored in Shared Preferences and for iOS app, in the Keychain.
It depends on how you define "mobile application". Any application running on a mobile device ? Web browsing running on a mobile device ? What is a mobile device to you ?
Anyways, the general short answer, is that you can detect the device type using the User-Agent sent in the HTTP headers. All popular mobile browsers sends this. But be aware, that:
It can be spoofed (easily)
Some applications (ie iPhone or Android apps and similar) can be written in such a way, that they don't send a user agent with the HTTP requests. Best practice mandates to send the User-Agent though.
I don't know of a more reliable way to do this; and as long as stuff happens over HTTP there generally won't be any way of knowing anything about the client for certain. For mostly all the use cases, you will be alright with looking at the User-Agent.
You can buy access to User-Agent databases containing various device data, if applicable, two of such being WURFL or DeviceAtlas.
I am developing an API that will be used by users of my customers. Here is what the flow will look like:
User of my cloud based service creates an API key.
User embeds the API key into their own custom applications.
User deploys the application to their own end users.
The application talks to our API.
I am looking for advice on how to secure this API. I see a few issues:
API key has to be embedded into the users application and is therefore vulnerable to being stolen and abused.
Once an API key is compromised, it can easily be disabled, but how will my users update their applications to use a new API key short of having to rebuild the application and redeploy.
Does anyone have any ideas on how to design this?
I may be mistaken but maybe you could have your customers' users talk to your customers' APIs instead. Basically, your customers would keep their secret key on their servers, and not embed them in the clients they give their users, so it couldn't be hijecked (unless their server was compromised of course). Then the users would talk to your API through your customers' APIs.
It would be slower and need more work on the part of your customers, but also safer.
Two solutions that I can see to this, although I'm sure there are more..
Use oauth's RSA signature method, and implement a secure certification exchange of keys using your "cloud based service" as the exchange mechanism (or a public cert provider).
Implement a service that allows clients to "renew" their consumer key/secret automatically, but then secure that mechanism using RSA or some other public key encryption method.
Both of these are not easy, and would require your user's applications to "phone home" in order to update their consumer keys.
In the future I think OAuth 2 will provide at least protocol definitions for things like this, but for now, if you're using OAuth 1.0a, what you want to do doesn't really fit into the spec very well (i.e. you have to design much of it yourself.)