I'm adding some web api to my project (using mvc web api) for our mobile clients.I'm using OWIN and Bearer Token (password grant type) for user authentication, as far as I'm concerned it's best practice for user authentication and resource authorization, but my issue is that how I can authenticate my clients (using a standardized approach) so that only actual and real clients can have access to services (even anonymous services)
for example we have two types of clients android and IOS apps, only these two must have access to web api
What is the best solution (practice) for doing so and does owin have any solution for it ???
what I've tried so far is generating a public key for each client and version and giving the keys to our mobile developers and they plug the key inside a certificate and send the key in each request
here is an example of the key for an android client
"StoreFrontType" : "AndroidApp"
"StoreFrontVersion" : "1.0.0.0"
"Client_Token" : "1vnM/XHDmIfv1yhftbnCnc8R92vRhSBBsciKzyHEVYmAI2bTpHqWsgmVBGel6Rd"
I had a conversation with our mobile developers and they said that this approach is better than nothing but not secure enough because mobile apps(specially android) source code and certificate can be decompiled and read easily so it's not secure enough to use my approach because by this approach if some one get the public key (by either decompiling source or reading certificate) they can send request and they will be known as a valid client
any help would be appreciated
It depends on what your threat model is. There's no perfect solution for this problem. You cannot trust the mobile device to keep secret, anything identifying the device as a trusted client.
If a legitimate user of your mobile client wants to get the token/secret identifying the device as a trusted client, he/she will be able to. They could then give the identifier and token away to anyone and they would then be able to identify as a legitimate client.
If that is not a real concern for you, you could use the OAuth2 client credentials flow.
OAuth2 defines the client credentials flow for clients to get access tokens on their own behalf, but this flow is only for trusted client (i.e. web applications that reside on a server).
Related
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 have a website and an API. The website allows anonymous people to browse the catalogue, but you must be logged in to post stuff.
I have built an API that exposes the same functionality. The API is used by a mobile app we are developing, but we are also going to allow other developers to use the API (i.e. it's publicly documented). The entire API is currently requires OAuth (2.0) authentication. To prevent abuse we use rate-limiting per OAuth client-id/user-id combination.
Now a new requirement for the mobile app has come down: The app should allow anonymous users to browse our catalogue. I am not sure how to implement this, without opening up our API to abuse.
Anonymous OAuth access
The first problem is allowing anonymous access. If we still want the entire API protected by OAuth then our mobile app will have to use the client-credentials grant type (posting a client-id and secret key). But we would have to store the client-id and secret in the app itself. This is not secure since it can easily be reverse engineered.
Alternatively, we could use dynamic client registration. As soon as an app is installed, it registers with an (undocumented) API to create an OAuth client for itself. Problem here is, how do I protect the client registration endpoint? A secret key again? Plus, this leads to a large amount of OAuth clients registered.
Remove OAuth from public endpoints
Alternatively, we could remove OAuth from the public endpoints all together (i.e. browsing the catalogue) and only require OAuth for posting stuff or managing an account. But how would I protect the API from abuse then? Without OAuth I cannot rate-limit based on client-id.
I am not sure that rate-limiting based on IP address would work. We expect many mobile app users and I fear that crappy (Moroccan) mobile telecom providers are NAT-ing a large amount of phone users behind just a few IP addresses. This would quickly exhaust any rate-limit that we set.
Is this correct? Or can I safely rate-limit on IP address for mobile users?
Alternative security mechanism
I could also implement a different authentication mechanism alongside OAuth. Something that allows our mobile phone app access to the API, which can distinguish (and rate-limit) different phones/users but which is safe from people just extracting a shared secret key from our mobile app binary.
Any suggestions on how to allow anonymous access to my API but still rate-limit effectively?
Since, the mobile app is installed on a device, if you configure a secret, then that secret will be common for all installations of the mobile app. Thus, derailing the purpose of a secret.
You should do dynamic registration. Here are the steps
Developer preconfigures the the following information with a trusted authority.
{
"software_id":"COMMON_VALUE_HERE",
"software_version": "OPTIONAL_BUILD_VERSION",
"client_name":"HUMAN_READABLE_CLIENT_NAME",
"client_uri":"OPTIONAL_FOR_CLIENT_CREDENTIALS",
"logo_uri":"OPTIONAL_FOR_CLIENT_CREDENTIALS",
"tos_uri":"OPTIONAL_TERMS_OF_USE"
}
The trusted authority generates a "software_statement" in exchange of the information that the developer provided. This contains the information that is constant for all installations of the native app.
After the app is installed on the user device, the app contacts the Authorization server for dynamic registration. The app posts the following to Authorization server
{
"redirect_uri" : "OPTIONAL_FOR_CLIENT_CREDENTIALS",
"scope": "SPACE SEPARATED SCOPES",
"software_statement": "MANDATORY"
}
The Authorization server verifies the information present in the "software_statement", generates and returns back a "client_id" and "client_secret" that are specific to the particular installation of software.
The client calls "POST" method on token endpoint with the newly received "client_id" and "client_secret", and receives an "access_token".
The client uses the "access_token" for accessing the "protected_resource".
The source of my answer is "oauth 2 in action" by Manning publication.
I've been digging through stackoverflow / security.stackexchange threads and getting no definite answers on providing a universal way for clients to securely consume RESTful services I'm am building through asp.net's web api. In searching for this answer, I see "authorization" and "authentication" used interchangeably, so I want to point out that I am merely wanting to verify both a requests identity and legitimacy. So, at this point, I am not authenticating users.
Amazon's model seems to be the model referenced when "rolling your own," but, in this context, I do understand Amazon has supplied the "papers" per say, so not much reinvention going on here. This post,
Designing a Secure REST (Web) API without OAuth, was super helpful.
What I gather is:
The application must require SSL requests, so a GET at "http://myapi.com/users/1" should be rejected with a bad request response letting the developer know https is required.
An app key / secret must be supplied by the client to verify who they are.
SSL + certificates is a good idea
Require a nonce value
When a client registers their app, require input of URL and IP that they will send requests from to verify upon receiving a request. My concern with this has been the portability of an external app, i.e. app is moved to new server with different IP and now it doesn't work.
I have few problems with 2 that, perhaps, my mind can't wrap itself around. First, isn't an app secret supposed to be secret? So, if a javascript client makes a request doesn't this compromise the app key's secrecy? Why have an app secret then when I can verify the requests identity through a combination of verifying app key, nonce value, and server ip? I do understand that a server side language such as php, ruby, or c#.net wouldn't expose the secret, but I would like this to be universally secure for JS and compiled languages alike.
Finally, Facebook has a developer security checklist telling developers to "Never include your App Secret in client-side or decompilable code," which would suggest an encrypted web.config or the like to me. This solution wouldn't work for exposing the REST service to anyone consuming via javascript.
Other threads I've combed through:
http://www.thebuzzmedia.com/designing-a-secure-rest-api-without-oauth-authentication/
https://developers.facebook.com/docs/facebook-login/security/
Best Practices for securing a REST API / web service
Security of REST authentication schemes
HTTP Basic Authentication instead of TLS client certification
RESTful Authentication
The way I secure my app is with OpenID Connect. For your example, the client you are talking about in #2 would be the RP (resource provider) and an authentication system like Google would be your OP (OpenID provider)
An app key / secret must be supplied by the client to verify who they are.
would actually be your application and your client secret would not leave your server any more than your /etc/passwd file. This secret is what is used by the RP to talk to the OP to get the data.
The flow in a nutshell is
User connects to your API endpoint e.g. /restapi
Your endpoint redirects the user to Google where you have registered your application
User signs into the OP (e.g. Google) and gets a code to pass to the RP
RP will go to OP to get openid information e.g. e-mail
RP will then use that openid information to look up its own authorization tables
Once RP validates the authorization for the user RP will provide the rest of the information.
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 currently developing a web application that is right now comprised of a front end which displays and interacts with the data using a REST API we have written. The only thing that will ever use the API is our front end website, and at some point a mobile app that we will develop.
I have done a lot of reading about how OAuth is the ideal mechanism for securing an API and at this point I am starting to have a good understanding of how it works.
My question is -- since I am never granting access to my API to a third-party client, is OAuth really necessary? Is there any reason it is advantageous? Furthermore, because the back end is simply the API, there is no gateway for a user to authenticate from (like if you were writing an app using the Twitter API, when a user authenticates they would be directed to the Twitter page to grant to access then redirected back to the client).
I am not really sure which direction to go in. It seems like there must be some approach halfway between http authentication and OAuth that would be appropriate for this situation but I'm just not getting it.
From my point of view, one of the scenarios that favor OAuth over other options is to work with untrusted clients, no matter if these are developed by you or a third party.
What's an untrusted client? Think from the point of who handles the credentials that grant access to your API.
For example, your web application could interact with your API in two falvors:
Your web app server side talks to your API. Your web app server is a trusted client because the credentials to access your API can only be access by whom have access to the server...You and your team. You could authenticate your web app server with a client_id and a client_secret.
You may want to make calls directly to your API from your Web app client, which runs on the end user's browser using JavaScript. The end user's browser is an untrusted client. If you were to deliver the credentials to your API down to the browser, anyone could check the JavaScript code and steal your credentials.
A third party Native App is also untrusted. A malicious developer that uses your API could save the credentials of and end user of your platform.
Your Native App is a trusted client and could manage the authentication with a simple username , password and a client id identifying your App.
How can OAuth help? OAuth Authorization code and Implicit grants can help you with this issue. These flows only work with clients that support a redirect, like a browser. And let you authenticate an untrusted client and a user against your Authorization Server to gain access to your Resource Server, your API, without exposing the credentials. Take a look at the RFC to see how it is done.
The good thing of OAuth is that it not only supports these redirect based authentication flows, but it also supports client credentials grant and user credentials grant. So an OAuth Authorization Server would cover all cases.
OAuth 2.0 originally seems like a PITA if you think about having to build a lot of it yourself, but most languages have some really solid OAuth 2.0 setups which you can just bolt in with varying amounts of fiddling. If you're using a framework like Laravel or RoR then it's barely any work.
PHP: http://oauth2.thephpleague.com/
Ruby (Rails or Grape): https://github.com/doorkeeper-gem/doorkeeper
If you don't want to redirect users as suggested in your post then ignore other comments and answers that talk about two legged flows. You can use the client_credentials grant type to have apps just provide their client id and secret in return for an access token, which is nice and easy.
I would ask how private are we talking, because if the only systems talking to it are within the backend and have no interaction with the outside world you could probably leave it wide open and just rely on the network to keep it safe (VPN/Firewall).
But if it's private in the sense of "our iPhone app uses it" then you definitely want to go with OAuth 2.0, or something like it.
2 legged OAuth is probably what you want to use. It's basically hashing a shared key, but you have the advantage of not having to write the code yourself.
Here's a related question: Two-legged OAuth - looking for information
You should use Oauth for mobile device to API layer communication.
However, there is no benefit of Oauth in this web UI layer to middle-layer access (machine to machine).
On the other hand there are some potential issues
Managing the access token expiry becomes a pain. Consider that your UI has to cache the access token across multiple nodes in a cluster. Refresh it when expired, and the fact that UI layer is negotiating security with backend will just take extra time once in a while.
In two legged Oauth (OAuth Client Credential as in v2.0) does not support any encryption. So you still need to send key and secret both to the server for getting an access token.
Backend has to implement issuing access token, refresh token, validating access token etc, without any significant benefit