Every article I've read vouching for the advantages of JWT state that one of these advantages is its ability for an auth system to be distributed across multiple servers. i.e . You aren't relying on a central repository of user auth details to do a lookup on every request.
However when it comes to implementation, I've read in many places that for added security you shouldn't just rely on the JWT signature verification itself, and that you should maintain a list of black or white list tokens generated by the server.
Doesn't this defeat the advantage I've listed above, as this list of tokens would need to be stored centrally where all servers can access it and it would require a lookup on each request?
How have people implemented this on their end?
You are making very good points in your question. Actually it would make sense to store an OAuth token at a central location in order to make it easier to implement signout/revoke functionality. If you just relied on the token signature you couldn't have possibly implemented such feature. Suppose that a user wanted to revoke an access token. In this case if you didn't have a central location/datastore for those tokens where you would have invalidated it and only relied on token signature, then the token would still have been valid.
So indeed, when you want to build more advanced systems that are dependent on OAuth tokens, a central store for those tokens is more than a must.
Related
I have familiarity with OAuth 2.0 / OpenID Connect but am new to WebAuthn. I am trying to understand how a scenario using those OAuth flows and connections would work using WebAuthn. I thought by mapping concepts from oauth to webauthn I would be able better understand the concepts.
I think similar to how in OAuth implicit grant flow a client may receive an id_token and access_token, in WebAuthn a client may receive a credential object from the Authenticator using navigator.credential.create.
The part I do not understand is how this credential can reliably be consumed by downstream services. In OAuth a client or server may send "access_tokens" and the receiving servers may request the public keys from the authorities to validate that it hasn't been tampered, is not expired, has correct audience, etc. This relies on the authorities having a publicly available /.well-known endpoint with the public keys.
However, I think because the keys are specific to the authenticator instead of a single shared public key it is not possible to have these be discoverable.
This is where I don't understand how credentials could be consumed by services. I thought the client would have to send the public key WITH the authenticator and client data but this is 3 pieces of information and awkward. Sending a single access_token seems actually cleaner.
I created a graphic to explain visually.
(It may have technical inaccuracies, but hopefully the larger point is made clearer)
https://excalidraw.com/#json=fIacaTAOUQ9GVgsrJMOPr,yYDVJsmuXos0GfX_Y4fLRQ
Here are the 3 questions embedded in the image:
What data does the client need to send to the server in order for the server to use the data? (Similar to sending access_token)
How would sever get the public key to decrypt data?
Which piece of data is appropriate / standardized to use as the stable user id?
As someone else mentioned - where there are a lot of commonalities between how WebAuthn and something like OpenID Connect work, they aren't really useful for understanding how WebAuthn works - they are better to explore after you understand WebAuthn.
A WebAuthn relying party does not have its own cryptographic keys or secrets or persistent configuration - it just has a relying party identifier, which is typically the web origin. The client (browser and/or platform) mediate between the relying party and authenticators, mostly protecting user privacy, consent, and providing phishing protection.
The relying party will create a new credential (e.g. key pair) with the authenticator of a user's choosing, be it a cell phone or a physical security key fob in their pocket. The response is the public key of a newly created key pair on the authenticator. That public key is saved against the user account by the RP.
In a future authentication, the authentication request results in a response signed by that public key. The private portion is never meant to leave the authenticator - at least not without cryptographic protections.
This does pair well with something like OpenID Connect. The registration is normally by web domain, which means that there could be a lot of manual registrations necessary (and potentially management, and recovery, and other IAM type activities) necessary. With OpenID Connect, you can centralize the authentication of several applications at a single point, and with it centralize all WebAuthn credential management.
I thought by mapping concepts from oauth to webauthn I would be able better understand the concepts.
This seems to be working against you - you're trying to pattern match WebAuthn onto a solution for a different kind of problem (access delegation). Overloaded terminology around "authentication" doesn't help, but the WebAuthn specification does make things a bit more clear when it describes what it means with "Relying Party":
Note: While the term Relying Party is also often used in other contexts (e.g., X.509 and OAuth), an entity acting as a Relying Party in one context is not necessarily a Relying Party in other contexts. In this specification, the term WebAuthn Relying Party is often shortened to be just Relying Party, and explicitly refers to a Relying Party in the WebAuthn context. Note that in any concrete instantiation a WebAuthn context may be embedded in a broader overall context, e.g., one based on OAuth.
Concretely: in your OAuth 2.0 diagram WebAuthn is used during step 2 "User enters credentials", the rest of it doesn't change. Passing the WebAuthn credentials to other servers is not how it's meant to be used, that's what OAuth is for.
To clarify one other question "how would sever get the public key to decrypt data?" - understand that WebAuthn doesn't encrypt anything. Some data (JS ArrayBuffers) from the authenticator response is typically base64 encoded, but otherwise the response is often passed to the server unaltered as JSON. The server uses the public key to verify the signature, this is either seen for the first time during registration, or retrieved from the database (belonging to a user account) during authentication.
EDIT: Added picture for a clearer understanding of how webauthn works, since it has nothing to do with OAuth2 / OpenID.
(source: https://passwordless.id/protocols/webauthn/1_introduction)
Interestingly enough, what I aim to do with Passwordless.ID is a free public identity provider using webauthn and compatible with OAuth2/OpenID.
Here is the demo of such a "Sign in" button working with OAuth2/OpenID:
https://passwordless-id.github.io/demo/
Please note that this is an early preview, still in development and somewhat lacking regarding the documentation. Nevertheless, it might be useful as working example.
That said, I sense some confusion in the question. So please let me emphasize that OAuth2 and WebAuthN are two completely distinct and unrelated protocols.
WebAuthN is a protocol to authenticate a user device. It is "Hey user, please sign me this challenge with your device to prove it's you"
OAuth2 is a protocol to authorize access to [part of] an API. It is "Hey API, please grant me permission to do this and that on behalf of the user".
OpenID builds on OAuth2 to basically say "Hey API, please allow me to read the user's standardized profile!".
WebauthN is not a replacement for OAuth2, they are 100% independent things. OAuth2 is to authorize (grant permissions) and is unrelated to how the user actually authenticates on the given system. It could be with username/password, it could be with SMS OTP ...and it could be with WebauthN.
There is a lot of good information in the other answers and comments which I encourage you to read. Although I thought it would be better to consolidate it in a single post which directly responds to the question from OP.
How does WebAuthN allow dependent web API's to access public key for decrypting credential without having to send the key?
There were problems with the question:
I used the word "decrypt" but this was wrong. The data sent is signed not encrypted and so key is not used to decrypted but verify the signature.
I was asking how a part of OAuth process can be done using WebAuthN however, this was misunderstanding. WebAuthN is not intended to solve this part of process so the question is less relevant and doesn't make sense to be answered directly.
Others have posted that WebAuthN can be used WITH OAuth so downstream systems can still receive JWTs and verify signatures as normal. How these two protocols are paired is a out of scope.
What data does the client need to send to the server in order for the server to use the data?
#Rafe answered: "table with user_id, credential_id, public_key and signature_counter"
See: https://www.w3.org/TR/webauthn-2/#authenticatormakecredential
How would server get the public key to decrypt data?
Again, decrypt is wrong word. Server is not decrypting only verifying signature
Also, the word server has multiple meanings based on context and it wasn't clarified in the question.
WebAuthN: For the server which acts as Relying Party in WebAuthN context, it will verify signature during authentication requests. However, the server in question was intended to mean the downstream APIs would not be part of WebAuthN.
OAuth: As explained by others, theses API servers could still be using OAuth and request public key from provider for verification and token contains necessary IDs and scopes/permissions. (Likely means able to re-use existing JWT middlewares)
Which piece of data is appropriate / standardized to use as the stable user id?
For WebAuthN the user object requires { id, name, displayName }. However, it intentionally does not try to standardize how the ID may propagated to downstream systems. That is up to developer.
See: https://www.w3.org/TR/webauthn-2/#dictdef-publickeycredentialuserentity
For OAuth
sub: REQUIRED. Subject Identifier. A locally unique and never reassigned identifier within the Issuer for the End-User
See: https://openid.net/specs/openid-connect-core-1_0.html#TokenResponse
Hopefully I didn't make too many technical inaccuracies. 😬
I'm developing my very first mobile application and I need advice. I created REST API in spring boot and it works great but I want to restrict access. It should be used only by my app. There is no user login it only gets data from the server.
Would be some API token enough or is there any other way how can I do this?
maybe it's a stupid question but I really need advice.
thanks
You can use these pointers -
Least Privilege:
An entity should only have the required set of permissions to perform the actions for which they are authorized, and no more. Permissions can be added as needed and should be revoked when no longer in use.
Fail-Safe Defaults:
A user’s default access level to any resource in the system should be “denied” unless they’ve been granted a “permit” explicitly.
Economy of Mechanism:
The design should be as simple as possible. All the component interfaces and the interactions between them should be simple enough to understand.
Complete Mediation:
A system should validate access rights to all its resources to ensure that they’re allowed and should not rely on the cached permission matrix. If the access level to a given resource is being revoked, but that isn’t reflected in the permission matrix, it would violate the security.
Open Design:
This principle highlights the importance of building a system in an open manner—with no secret, confidential algorithms.
Separation of Privilege:
Granting permissions to an entity should not be purely based on a single condition, a combination of conditions based on the type of resource is a better idea.
Least Common Mechanism:
It concerns the risk of sharing state among different components. If one can corrupt the shared state, it can then corrupt all the other components that depend on it.
Psychological Acceptability:
It states that security mechanisms should not make the resource more difficult to access than if the security mechanisms were not present. In short, security should not make worse the user experience.
Always Use HTTPS (This is hard)
By always using SSL, the authentication credentials can be simplified to a randomly generated access token that is delivered in the username field of HTTP Basic Auth. It’s relatively simple to use, and you get a lot of security features for free.
If you use HTTP 2, to improve performance – you can even send multiple requests over a single connection, that way you avoid the complete TCP and SSL handshake overhead on later requests.
Use Password Hash
Passwords must always be hashed to protect the system (or minimize the damage) even if it is compromised in some hacking attempts. There are many such hashing algorithms which can prove really effective for password security e.g. PBKDF2, bcrypt and scrypt algorithms.
Never expose information on URLs
Usernames, passwords, session tokens, and API keys should not appear in the URL, as this can be captured in web server logs, which makes them easily exploitable.
https://api.domain.com/user-management/users/{id}/someAction?apiKey=abcd123456789 //Very BAD !!
The above URL exposes the API key. So, never use this form of security.
Consider OAuth
Though basic auth is good enough for most of the APIs and if implemented correctly, it’s secure as well – yet you may want to consider OAuth as well. The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf.
Consider Adding Timestamp in Request
Along with other request parameters, you may add a request timestamp as an HTTP custom header in API requests. The server will compare the current timestamp to the request timestamp and only accepts the request if it is within a reasonable timeframe (1-2 minutes, perhaps).
This will prevent very basic replay attacks from people who are trying to brute force your system without changing this timestamp.
Input Parameter Validation
Validate request parameters on the very first step, before it reaches to application logic. Put strong validation checks and reject the request immediately if validation fails. In API response, send relevant error messages and examples of correct input format to improve user experience.
You can use this as a checklist while making a rest API
Introduction
So in my developer team, we need two server-based applications one located in my company architecture let's call it company server (i.e. resource and authorization server in OAuth2 terminology) and the second one in customer architecture let's call it customer server (i.e client and resource owner). The customer server is loading data from the company server so my company server needs to authenticate it somehow.
My team decides to apply OAuth2 standard with authorization and resource server in a single monolith application, without even thinking of benefits. This would, of course, take more time to implement than a simple constant key stored in the header. So I wonder what are benefits of that solution.
I know that Basic Authentication needs user:password base64-encoded in every request but the customer server is a single user so token would be in fact constant key stored in the header and I will use that terminology in terms of simplicity.
Argument - Microservices
In M2M (machine-to-machine) communication according to this article, customer server should obtain the token by providing client_id and client_secret from authorization server then you can use with multiple resource servers. The first argument I see is that OAuth2 pattern allows us to use multiple resource servers without additionally reimplementing authorization in each of them (because token is JWT or resource server is checking token against authorization) but in our case we have only one monolithic company server that is responsible for being resource and authorization so I see no benefits of that.
Argument - Man-in-the-middle protection
The other argument of using OAuth2 is protection against man-in-the-middle attack if someone intercepts token. The authorization server can invalidate token (directly in storage or in case of signed JWT by short expiry time) and prevent using compromised token. But...
Connection between servers is SSL secured
There's no way to steal token from storage like in a web-based or mobile-based application because key is located on the server-side itself.
Summary
So I can't think of any security benefits using OAuth2 compared to using the constant key in every request in this situation.
Security is mostly a chicken-egg problem. You encrypt secrets with encryption key and then again you think how do we handle the encryption key in a secured way. Don't assume here that TLS/SSL is infallible. But the core objective has always been to reduce the attack surface and make it more difficult for malicious users to break the system.
Even when there is no "Man in the Middle", when you send the password with every request, both the receiving side and the sending side keep the password in memory. It leaves more opportunity for an attacker to get hold of the password. A simple memory dump can expose the password.
In case of tokens, you don't always need the private key in memory to verify the token signature. You can cache the valid tokens at the server end and simply do a string match. Or you can use a public private key pair.
So, it's okay not to use OAuth2, if the security requirements are not stringent enough to justify the development effort required for a more secured solution. But it is better to use proven best practices and solutions.
Looking at the Oauth2 specification, it says in section 6:
... the refresh token is bound to the client to which it was issued.
However, I can't find anything in the specification the explicitly states that the token should be bound to the requesting client also. I am assuming this to be the case, and the Introspection Extension seems to support that assumption, but I want to know if that is correct.
As an example, say I am using two applications that use Google as the Oauth2 Authorization Server. I'm assuming that Google will issue two different tokens, one to each application, and that the tokens can only be used by the client to which they were issued because they are bound to that client.
An access token can have various implementations. The one that is most widely adopted today is the "Bearer" token, in RFC 6750 https://www.rfc-editor.org/rfc/rfc6750. A Bearer token is not bound to the Client on purpose: it makes it easy to implement, lowers the barrier for adoption and caters for a wide range of use cases.
Assuming that a Bearer token cannot be easily stolen, it is acceptable to avoid binding it to a specific Client: the intended Client could indeed share the access token with another Client but it could just as well share the data that the access token permits access to if the token was bound.
In environments that demand higher security one could use a token that is bound to the Client as defined in RFC 7800 https://www.rfc-editor.org/rfc/rfc7800.
Yes, I think it is implicit in the specification that the access token should only be used by the application that the user authorized. Putting it differently - having something other than the authorized application use the token to access user data is pretty much the definition of a privacy failure, and is what authorization protocols are explicitly designed to prevent in the first place.
Now, in practice, I think that having one application use the access token from another would work fine in many OAuth 2.0 implementations. I don't thing the Token Introspection extension is widely used, and most access tokens are designed to be self-validating. Indeed, that's the reason why token stealing is a security risk. By contrast, the refresh token should only be useful when combined with the client secret, so it's "bound" to the client technically as well as philosophically.
I am creating an OAuth server which issues tokens to users. However, I don't want to store tokens in the database, and I want the processing to be fast.
What I'm thinking is to include various information in the token, so that when I decrypt it, the information is already enough to check for permissions and scopes.
I'm a little worried about the token's length growing as I add more scopes.
Is this a good idea? If not, what can you recommend?
What you are talking here is about InMemoryTokenStore which is the default implementation. Also Oauth2 already maintains the information required to check permissions and scopes in token in form of different access roles provided by authorization server to various clients. I think you don't need to explicitly store anything in token.