There is a lot of good content on the internet that explains how to secure a Spring API with Keycloak: Create a Client that represents the API Service in Keycloak and use a link like the one below to get the access and refresh token:
<Domain>/auth/realms/<realm>/protocol/openid-connect/auth/{some parameters}
This yields both tokens. So far so good.
Now, however, I am not sure how the flow for the frontend accessing the API should look like.
Should the frontend directly access this endpoint and, therefore, obtain the access and refresh token? That would mean that the API can only have the access-type public because there is no way to store the client (the API) secret securely.
Or should there be a third server that somehow stores the refresh token for each user, that the user can call if his access token is no longer valid. This server would then use the client's refresh token (and the client secret that could be stored securely, since it would be in the backend) to get a new access token from Keycloak and would forward it to the user.
I guess the main question that I am asking is, whether the client/user should get the refresh token.
If one needs to implement a logic according to the second option, I would be interested in a link or description of how something like this can be done in Spring.
I think, in either case you need to use the Authorization Code Flow. The implicit flow, which was recommended for SPAs (frontends without a backend server) in former versions of OAuth2 must not be used anymore.
The best option is to have a backend server, so the user retrieves the auth code via redirection and the backend server exchanges this auth code with the access and refresh tokens (and keep them without forwarding them to the frontend).
If there is no backend in place and your frontend needs to retrieve and hold the tokens directly, I would recommend to use the Authorization Code Flow with a public client and the PKCE extension (which - put simply - ensures that the entity asking for the auth code is the same as the entity asking for the tokens and that the auth code was not stolen and used by a foreign entity). There are several sources with more detailed explanations, which might help you, for example: https://auth0.com/docs/flows/authorization-code-flow-with-proof-key-for-code-exchange-pkce
Hope this helps you with your architectural considerations.
I have a mobile app which talks to an ASP WebAPI on the back-end.
I've implemented the token flow authentication (with the help of Taiseer's guide).
Still there is one concept I can't grasp my mind around: CleintId and ClientSecret.
From what I understand the client secret (along with client id) is meant to
block access to the end point in my API that produces tokens. This way the end point is protected from malicious users trying to poke around the API and try to gain some information by invoking it with various inputs.
Meaning, only clients which hold the secret can start an authenticaon flow. And in my case, I have only one client which is a mobile app, and it's secret is stored in a secure place (KeyChain for iOs). But I've read that those key chains can be easily dumped and dissect for the secret.
So the conclusion I came up with, is that I can get rid of the whole client secret logic, mainly leaving ValidateClientAuthentication() blank:
public async override Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
{
context.Validated();
return;
}
And to me it dose not seem like a security hole, but just a thin layer in the flow that is gone now. Because, again, the client secret can be easily revealed by any malicious user holding a mobile device with the app installed, and once he gets it this layer of security is useless.
Are those assumptions are incorrect ?
Can I leave the ValidateClientAuthentication() method blank ?
As you already figured out, mobile applications cannot keep their credentials private because they can be extracted from the application binaries. Not to mention that requests can be easily intercepted using a proxy server and a traffic analyzer like Fiddler or Wireshark.
With the authorization code flow (1) or the resource owner password credentials grant, client authentication is not mandatory if the client cannot safely store its credentials and thus cannot be considered as a "confidential" application (see https://www.rfc-editor.org/rfc/rfc6749#section-4.1.3 and https://www.rfc-editor.org/rfc/rfc6749#section-4.3.2).
For non-confidential applications, it's safe to call context.Validated().
Personally, I try to avoid the resource owner password credentials grant as much as possible as it clearly defeats the purpose of OAuth2: keeping your password confidential and giving constrained authorizations. If your app is fully trusted, it shouldn't be a problem, though.
In practice, using the authorization code flow without enforcing client authentication is extremely rare, as it's simpler to use the implicit flow with mobile client applications, that offers a similar security level in this case (not to mention that it avoids a second roundtrip to the token endpoint).
I have been reading about JWT.
But from what I read it is not an authentication mechanism but more like a crucial component in a Authentication mechanism.
I have currently implemented a solution which works, but it was just to try out JWT and see how it works. But what I am after now is how one should make use of it. From my experience of it its basically just an encryption mechanism that gives you a unique encrypted key. You are also able to put information inside of this token.
I am wanting to implement it in terms on a ASP.NET web api 2 to be consumed by a mobile application.
So step 1:
app => Server : Login (user, pasword)
Server => app : Login OK, heres your JWT
app => server : Get my profile (sends JWT with request)
Server then decrypts JWT and determines the requests Identity.
Now this is just my understanding of it, Look I could be on the totally wrong path.
Is the Ideal of JWT so that you dont have to authenticate on every request? I just authenticate the users credentials once (on the initial login) and there on after the server can simply use JWT and no have to lookup the users pw and user in the DB?
I just want to use the JWT to Identity who the user is. I will then authorize then after i have authenticated them. As I know there is a big confused with the new MVC and Authentication and Authorization.
So what my question comes down to.
How can I safely and effectively Implement a Authentication Mechanism Using JWT?
I don't want to just cough something up that seems to work and not have any Idea of the security implications. I am sure that there exists a source some where that has possibly designed a secure mechanism that would suit my requirements.
My requirements are:
Must only have to check db for users credentials once off per session? Due to the use of bcrypt using a lot of resources to compare passwords.
Must be able to identify the user from their request. (I.e who they are, userId will be sufficient) and preferably without accessing the DB as well
Should be as low overhead as possible, with regards to resources on the server side processing the request.
If an intruder had to copy a devices previous request, then he should not be able to access the real users data. (obviously)
Thanks
Your understanding of JWTs is good. But here are a couple corrections and some recommendations.
Authentication and Authorization
JWTs have nothing to do with authentication. Hitting your DB and hashing passwords only happens when you authenticate on creation of the JWT. This is orthogonal to JWTs and you can do that in any way you like. I personally like Membership Reboot, which also has a good example of using JWTs.
Theoretically, you could have the user enter a password once a year and have the JWT be valid that entire year. This most likely not the best solution, if the JWT gets stolen at any point the users resources would be compromised.
Encryption
Tokens can, but don't have to be encrypted. Encrypting your tokens will increase the complexity of your system and amount of computation your server needs to read the JWTs. This might be important if you require that no one is able to read the token when it is at rest.
Tokens are always cryptographically signed by the issuer to ensure their integrity. Meaning they cannot be tampered with by the user or a third party.
Claims
Your JWTs can contain any information you want. The users name, birthdate, email, etc. You do this with claims based authorization. You then just tell your provider to make a JWT with these claims from the Claims Principle. The following code is from that Membership Reboot example and it shows you how this is done.
public override Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
{
var svc = context.OwinContext.Environment.GetUserAccountService<UserAccount>();
UserAccount user;
if (svc.Authenticate("users", context.UserName, context.Password, out user))
{
var claims = user.GetAllClaims();
var id = new System.Security.Claims.ClaimsIdentity(claims, "MembershipReboot");
context.Validated(id);
}
return base.GrantResourceOwnerCredentials(context);
}
This allows you to control with precision whom is accessing your resources, all without hitting your processor intensive authentication service.
Implementation
A very easy way to implement a Token provider is to use Microsoft's OAuth Authorization Server in your WebAPI project. It give you the bare bones of what you need to make a OAuth server for your API.
You could also look into Thinktecture's Identity Server which would give you much easier control over users. For instance, you can easily implement refresh tokens with identity server where the user is authenticated once and then for a certain amount of time (maybe a month) they can continue getting short lived JWTs from the Identity Server. The refresh tokens are good because they can be revoked, whereas JWTs cannot. The downside of this solution is that you need to set up another server or two to host the Identity service.
To deal with your last point, that an intruder should not be able to copy the last request to get access to a resource, you must use SSL at a bare minimum. This will protect the token in transport.
If you are protecting something extremely sensitive, you should keep the token lifetime to a very short window of time. If you are protecting something less sensitive, you could make the lifetime longer. The longer the token if valid, the larger the window of time a attacker will have to impersonate the authenticated user if the user's machine is compromised.
I've written detailed blog post about configuring the OWIN Authorization server to issue signed JSON Web Tokens instead of default token. So the resource servers (Audience) can register with the Authorization server, and then they can use the JWT tokens issued by Token issuer party without the need to unify machineKey values between all parties. You can read the post JSON Web Token in ASP.NET Web API 2 using Owin
For the formal concept . The Authentication is the process of verifying who a user is, while authorization is the process of verifying what they have access to.
Let’s see the real life example
Imagine that your neighbor has asked you to feed his pets while he is away. In this example, you have the authorization to access the kitchen and open the cupboard storing the pet food. However, you can’t go into your neighbor’s bedroom as he did not explicitly permit you to do so. Even though you had the right to enter the house (authentication), your neighbor only allowed you access to certain areas (authorization).
For more detailed and for users who like more STEP BY STEP implementation on practical use of JSON Web Token in WEB API. This is must read post Secure WebAPI Using JSON WEB TOKEN
Updated to use: System.IdentityModel.Tokens.Jwt -Version 5.1.4
Is using sessions in a RESTful API really violating RESTfulness? I have seen many opinions going either direction, but I'm not convinced that sessions are RESTless. From my point of view:
authentication is not prohibited for RESTfulness (otherwise there'd be little use in RESTful services)
authentication is done by sending an authentication token in the request, usually the header
this authentication token needs to be obtained somehow and may be revoked, in which case it needs to be renewed
the authentication token needs to be validated by the server (otherwise it wouldn't be authentication)
So how do sessions violate this?
client-side, sessions are realized using cookies
cookies are simply an extra HTTP header
a session cookie can be obtained and revoked at any time
session cookies can have an infinite life time if need be
the session id (authentication token) is validated server-side
As such, to the client, a session cookie is exactly the same as any other HTTP header based authentication mechanism, except that it uses the Cookie header instead of the Authorization or some other proprietary header. If there was no session attached to the cookie value server-side, why would that make a difference? The server side implementation does not need to concern the client as long as the server behaves RESTful. As such, cookies by themselves should not make an API RESTless, and sessions are simply cookies to the client.
Are my assumptions wrong? What makes session cookies RESTless?
First of all, REST is not a religion and should not be approached as such. While there are advantages to RESTful services, you should only follow the tenets of REST as far as they make sense for your application.
That said, authentication and client side state do not violate REST principles. While REST requires that state transitions be stateless, this is referring to the server itself. At the heart, all of REST is about documents. The idea behind statelessness is that the SERVER is stateless, not the clients. Any client issuing an identical request (same headers, cookies, URI, etc) should be taken to the same place in the application. If the website stored the current location of the user and managed navigation by updating this server side navigation variable, then REST would be violated. Another client with identical request information would be taken to a different location depending on the server-side state.
Google's web services are a fantastic example of a RESTful system. They require an authentication header with the user's authentication key to be passed upon every request. This does violate REST principles slightly, because the server is tracking the state of the authentication key. The state of this key must be maintained and it has some sort of expiration date/time after which it no longer grants access. However, as I mentioned at the top of my post, sacrifices must be made to allow an application to actually work. That said, authentication tokens must be stored in a way that allows all possible clients to continue granting access during their valid times. If one server is managing the state of the authentication key to the point that another load balanced server cannot take over fulfilling requests based on that key, you have started to really violate the principles of REST. Google's services ensure that, at any time, you can take an authentication token you were using on your phone against load balance server A and hit load balance server B from your desktop and still have access to the system and be directed to the same resources if the requests were identical.
What it all boils down to is that you need to make sure your authentication tokens are validated against a backing store of some sort (database, cache, whatever) to ensure that you preserve as many of the REST properties as possible.
I hope all of that made sense. You should also check out the Constraints section of the wikipedia article on Representational State Transfer if you haven't already. It is particularly enlightening with regard to what the tenets of REST are actually arguing for and why.
First, let's define some terms:
RESTful:
One can characterise applications conforming to the REST constraints
described in this section as "RESTful".[15] If a service violates any
of the required constraints, it cannot be considered RESTful.
according to wikipedia.
stateless constraint:
We next add a constraint to the client-server interaction:
communication must be stateless in nature, as in the
client-stateless-server (CSS) style of Section 3.4.3 (Figure 5-3),
such that each request from client to server must contain all of the
information necessary to understand the request, and cannot take
advantage of any stored context on the server. Session state is
therefore kept entirely on the client.
according to the Fielding dissertation.
So server side sessions violate the stateless constraint of REST, and so RESTfulness either.
As such, to the client, a session cookie is exactly the same as any
other HTTP header based authentication mechanism, except that it uses
the Cookie header instead of the Authorization or some other
proprietary header.
By session cookies you store the client state on the server and so your request has a context. Let's try to add a load balancer and another service instance to your system. In this case you have to share the sessions between the service instances. It is hard to maintain and extend such a system, so it scales badly...
In my opinion there is nothing wrong with cookies. The cookie technology is a client side storing mechanism in where the stored data is attached automatically to cookie headers by every request. I don't know of a REST constraint which has problem with that kind of technology. So there is no problem with the technology itself, the problem is with its usage. Fielding wrote a sub-section about why he thinks HTTP cookies are bad.
From my point of view:
authentication is not prohibited for RESTfulness (otherwise there'd be little use in RESTful services)
authentication is done by sending an authentication token in the request, usually the header
this authentication token needs to be obtained somehow and may be revoked, in which case it needs to be renewed
the authentication token needs to be validated by the server (otherwise it wouldn't be authentication)
Your point of view was pretty solid. The only problem was with the concept of creating authentication token on the server. You don't need that part. What you need is storing username and password on the client and send it with every request. You don't need more to do this than HTTP basic auth and an encrypted connection:
Figure 1. - Stateless authentication by trusted clients
You probably need an in-memory auth cache on server side to make things faster, since you have to authenticate every request.
Now this works pretty well by trusted clients written by you, but what about 3rd party clients? They cannot have the username and password and all the permissions of the users. So you have to store separately what permissions a 3rd party client can have by a specific user. So the client developers can register they 3rd party clients, and get an unique API key and the users can allow 3rd party clients to access some part of their permissions. Like reading the name and email address, or listing their friends, etc... After allowing a 3rd party client the server will generate an access token. These access token can be used by the 3rd party client to access the permissions granted by the user, like so:
Figure 2. - Stateless authentication by 3rd party clients
So the 3rd party client can get the access token from a trusted client (or directly from the user). After that it can send a valid request with the API key and access token. This is the most basic 3rd party auth mechanism. You can read more about the implementation details in the documentation of every 3rd party auth system, e.g. OAuth. Of course this can be more complex and more secure, for example you can sign the details of every single request on server side and send the signature along with the request, and so on... The actual solution depends on your application's need.
Cookies are not for authentication. Why reinvent a wheel? HTTP has well-designed authentication mechanisms. If we use cookies, we fall into using HTTP as a transport protocol only, thus we need to create our own signaling system, for example, to tell users that they supplied wrong authentication (using HTTP 401 would be incorrect as we probably wouldn't supply Www-Authenticate to a client, as HTTP specs require :) ). It should also be noted that Set-Cookie is only a recommendation for client. Its contents may be or may not be saved (for example, if cookies are disabled), while Authorization header is sent automatically on every request.
Another point is that, to obtain an authorization cookie, you'll probably want to supply your credentials somewhere first? If so, then wouldn't it be RESTless? Simple example:
You try GET /a without cookie
You get an authorization request somehow
You go and authorize somehow like POST /auth
You get Set-Cookie
You try GET /a with cookie. But does GET /a behave idempotently in this case?
To sum this up, I believe that if we access some resource and we need to authenticate, then we must authenticate on that same resource, not anywhere else.
Actually, RESTfulness only applies to RESOURCES, as indicated by a Universal Resource Identifier. So to even talk about things like headers, cookies, etc. in regards to REST is not really appropriate. REST can work over any protocol, even though it happens to be routinely done over HTTP.
The main determiner is this: if you send a REST call, which is a URI, then once the call makes it successfully to the server, does that URI return the same content, assuming no transitions have been performed (PUT, POST, DELETE)? This test would exclude errors or authentication requests being returned, because in that case, the request has not yet made it to the server, meaning the servlet or application that will return the document corresponding to the given URI.
Likewise, in the case of a POST or PUT, can you send a given URI/payload, and regardless of how many times you send the message, it will always update the same data, so that subsequent GETs will return a consistent result?
REST is about the application data, not about the low-level information required to get that data transferred about.
In the following blog post, Roy Fielding gave a nice summary of the whole REST idea:
http://groups.yahoo.com/neo/groups/rest-discuss/conversations/topics/5841
"A RESTful system progresses from one steady-state to the
next, and each such steady-state is both a potential start-state
and a potential end-state. I.e., a RESTful system is an unknown
number of components obeying a simple set of rules such that they
are always either at REST or transitioning from one RESTful
state to another RESTful state. Each state can be completely
understood by the representation(s) it contains and the set of
transitions that it provides, with the transitions limited to a
uniform set of actions to be understandable. The system may be
a complex state diagram, but each user agent is only able to see
one state at a time (the current steady-state) and thus each
state is simple and can be analyzed independently. A user, OTOH,
is able to create their own transitions at any time (e.g., enter
a URL, select a bookmark, open an editor, etc.)."
Going to the issue of authentication, whether it is accomplished through cookies or headers, as long as the information isn't part of the URI and POST payload, it really has nothing to do with REST at all. So, in regards to being stateless, we are talking about the application data only.
For example, as the user enters data into a GUI screen, the client is keeping track of what fields have been entered, which have not, any required fields that are missing etc. This is all CLIENT CONTEXT, and should not be sent or tracked by the server. What does get sent to the server is the complete set of fields that need to be modified in the IDENTIFIED resource (by the URI), such that a transition occurs in that resource from one RESTful state to another.
So, the client keeps track of what the user is doing, and only sends logically complete state transitions to the server.
As I understand, there are two types of state when we are talking about sessions
Client and Server Interaction State
Resource State
Stateless constraint here refers to the second type in Rest. Using cookies (or local storage) does not violate Rest since it is related to the first.
Fielding says: 'Each request from client to server must contain all of the information necessary to understand the request, and cannot take advantage of any stored context on the server. Session state is therefore kept entirely on the client.'
The thing here is that every request to be fulfilled on the server needs the all necessary data from the client. Then this is considered as stateless. And again, we're not talking about cookies here, we're talking about resources.
HTTP transaction, basic access authentication, is not suitable for RBAC, because basic access authentication uses the encrypted username:password every time to identify, while what is needed in RBAC is the Role the user wants to use for a specific call.
RBAC does not validate permissions on username, but on roles.
You could tric around to concatenate like this: usernameRole:password, but this is bad practice, and it is also inefficient because when a user has more roles, the authentication engine would need to test all roles in concatenation, and that every call again. This would destroy one of the biggest technical advantages of RBAC, namely a very quick authorization-test.
So that problem cannot be solved using basic access authentication.
To solve this problem, session-maintaining is necessary, and that seems, according to some answers, in contradiction with REST.
That is what I like about the answer that REST should not be treated as a religion. In complex business cases, in healthcare, for example, RBAC is absolutely common and necessary. And it would be a pity if they would not be allowed to use REST because all REST-tools designers would treat REST as a religion.
For me there are not many ways to maintain a session over HTTP. One can use cookies, with a sessionId, or a header with a sessionId.
If someone has another idea I will be glad to hear it.
i think token must include all the needed information encoded inside it, which makes authentication by validating the token and decoding the info
https://www.oauth.com/oauth2-servers/access-tokens/self-encoded-access-tokens/
No, using sessions does not necessarily violate RESTfulness. If you adhere to the REST precepts and constraints, then using sessions - to maintain state - will simply be superfluous. After all, RESTfulness requires that the server not maintain state.
Sessions are not RESTless
Do you mean that REST service for http-use only or I got smth wrong? Cookie-based session must be used only for own(!) http-based services! (It could be a problem to work with cookie, e.g. from Mobile/Console/Desktop/etc.)
if you provide RESTful service for 3d party developers, never use cookie-based session, use tokens instead to avoid the problems with security.
I'm trying to make a web service secure.
It's not for a bank or anything of that sort, but the organization using it may lose some money if the service will be used by someone not authorized (it's hard to tell exactly how much..).
The purpose is not to allow unauthorized applications to use any method (other than "GetChallenge". for users authentication there is a different mechanism which checks for username and password. I actually combined the two, but they serve different purposes):
So here's what I do:
I send a (ASP.NET) session key (for everyone to read. ASP.NET's session Is 15 randomly generated bytes, it lives for 20 minutes unless prolonged, and ASP.NET will not receive any request without it).
In my SignIn method, apart from username and password (which anyone can acquire, since it's a part of a public site), I receive a third parameter - the session key hashed by md5 algorithm with 6 bytes as salt.
And only if the hash is correct (I'm hashing and comparing it on the server side) - I let the users sign in.
From then on in every method, I check if the user is signed in.
Added: The username and password are sent as clear text, and that's not a problem (not the one I'm addressing at least). The problem is for someone (other than the company we're working with) writing an application which uses my web service. The web service should only be used by an authorized application.
Also, the session id is sent back and forth with every request and response (as a part of ASP.NET session mechanism. That's how ASP.NET knows to "track" a session specific for a user). Sorry for not clarifying that from the first place.
(irrationally thought it was obvious).
How strong and effective is that security strategy?
Thanks.
Updated based on your edit and comment
It's pretty secure and is very similar to the approach used by Google, Facebook and others for their API keys. Except...
Session ID plain text potential issue
I would recommend against using Session ID as part of a security mechanism.
The one issue is with passing the session key in plain text across the network. There is potential that this could open up some Session hijack and other attacks.
From the Microsoft Docs:
The SessionID is sent between the server and the browser in clear text, either in a cookie or in the URL. As a result, an unwanted source could gain access to the session of another user by obtaining the SessionID value and including it in requests to the server. If you are storing private or sensitive information in session state, it is recommended that you use SSL to encrypt any communication between the browser and server that includes the SessionID.
As you are using the Session ID as part of your security mechanism I would say that is sensitive data.
One way to ensure someone doesn't get hold of your session key is to run your service on HTTPS. Personally I would avoid using the Session ID in this way and generating a non-related value instead.
Recommended change
Follow more closely the model used by Google and the like. Generate a new GUID for each application, store the GUID in a database on the server, pass the GUID in each request to your server from the client.
Benfits:
Identifies the client application uniquely, allowing you to track and manage usage per client nicely
Easily disable any client by removing the GUID from your data store
No sensitive data on the wire
I would still run the service on HTTPS as it's easy to setup and gives the added benefit of protecting any other data you send to your service.
The purpose of encryption is not to
allow unauthorized applications to use
any method
Wrong. The purpose of encryption it to prevent the understanding of data whilst either in transit or stored. It prevents data being 'useable' by those that do not have the means to decrypt.
What you are describing is something similar to a public/private key system. You're making your session key available to everyone. Then only after they've md5 with the correct salt (as per your server side comparison) you're then trusting that source.
You've got NO authentication here except for username and password. Also your data isn't encrypted during transit. I fail to see how this is at all secure.
I think you're best bet is to use an SSL certificate (so your web service is running over HTTPS) along with the username and password. If you want to be doubly secure you might want to go down the route of checking source IP ranges and login locations as an additional check. Perhaps a forced password change interval will help in the case that consumers are passing credentials to a third party + audit how the web service is actually being used.
As a side note if you want to hash something don't use MD5, its broken.
From a web services perspective the ideal way to use authentication or provide security to your service is something like this: Web Service Authentication (Token and MD5 Hashing to encrypt password).
The way you describe it, it does not seem secure at all.
What is the point of letting the SignIn method accept a hashed session key, if the session key is public ("for everyone to read")?
Plus: "in every method, I check if the user is signed in. " How do you check that?
A common (and reasonably secure) strategy would be to generate a (unique, sufficiently long and random) session ID server-side, and send it to the client after it has authenticated. Then check every client request and only accept it if it contains the session ID. To do this, either embed the ID into all links on every page, or set it as a cookie, depending on what's easier for you.
On logout, just delete the session ID on the server.
That way, no one can invoke any method without a valid session.