Maybe a dumb question on standalone authorization services: does the authorization service end up having a representation for every single object in all of the rest of your datastores? (e.g. every document, every blob of storage, every user in every org).
If so, does that become a chokepoint in a distributed microservice architecture? Or can that be avoided with an in-process or sidecar architecture in which a given microservice's objects are not separately referenced in auth persistence? If not, how do folks determine which objects to register with the auth service and which to handle independently?
A Zanzibar-style service does not need _every_ object from your DB replicated into it, but only the relationships between the objects that matter for authorizing access. Many of these relationships require little/no metadata in your DB so they can live _solely_ in Zanzibar rather than being in both your DB and Zanzibar. This is pretty great because when permissions requirements change, you can often address them by only changing the Zanzibar schema, completely avoiding a database migration.
>does that become a chokepoint in a distributed microservice architecture?
It actually does the opposite because now all of your microservices can query Zanzibar at any time to get answers to authorization questions that were previously isolated to only a single application.
Full disclosure: I work on https://authzed.com (YC W21) -- a permission system as a service inspired by Zanzibar. We're also planning on doing a PapersWeLove NYC on Zanzibar in the coming months, so stay tuned!
As with everything, it depends on your requirements.
Say your goal is to externalize just your authorization policies from your code. A simple implementation might look like an OPA sidecar to your services, with the policy itself being sourced from a separate control plane - this might be something as simple as a centrally-managed S3 bucket.
The service implementation provides the attributes to OPA to allow it to evaluate the authorization policy as part of the query. e.g. which groups is this user in, what document are they accessing, is this a read, write or delete operation.
If you want to externalize sourcing of the attributes as well, that becomes more complicated. Now you need your authorization framework to know that Bob is in "Accounting" or that quarter_end_results.xls is a document of type "Financial Results".
You can either go push or pull for attribute sourcing.
The push model is to have the relevant attribute universe delivered to each of the policy decision points, along with the policy itself. This improves static stability, as you reduce the number of real-time dependencies required for authorization queries but can be a serious data distribution and management problem - particularly if you need to be sure that data isn't going stale in some sidecar process somewhere for some reason.
The pull model is to have an attribute provider that can you can query as necessary; probably backed with an attribute cache for sanity's sake. The problems are basically the opposite set - liveness is guaranteed but static stability is more complicated.
The methods are not equivalent: in particular, the pull model is sufficient to answer simple authorization questions like 'can X do Y to Z?' - we pull the attributes of X, Y and Z and evaluate the authorization policy.
However, if you need to answer questions like 'to which Z can X do Y?', how does that work? For simple cases you may be able to iterate over the universe of Z's asking the prior question; but it generalizes poorly.
I've been writing about application authorization here: https://www.osohq.com/academy/chapter-2-architecture (I'm CTO at Oso, but these guides are not Oso specific). It covers this in the later part of the guide.
Depending on your requirements, yes that's kind of what happens if you want to centralise. It can make sense for Google-scale problems where you really do need to handle the complex graph of relationships between all users and resources, and doing that in any one service is non-trivial.
In practice though, a lot of service-oriented architectures can get the same benefits by having a central user management service, and keeping most of the authorization in each service. That central service can provide information like what organizations/teams/roles etc. the user belongs to, and then the individual services can make decisions based on that data.
This is the approach I covered with the hybrid approach. With this you can still implement most complex authorization models.
This is a really interesting question that gets at the heart of service federation.
I don't know the answer for Zanzibar, but take a look at how AWS IAM solves it. IAM has very few strong opinions in its model of the world (essentially it divides the world into AWS account ID namespaces and AWS service names/namespaces, and there's not much detail beyond that). Everything else is handled through symbolic references (via string/wildcard matching) to principals, resources, and actions in the JSON policies, as well as variables in policy evaluation contexts (and conditions, which are predicates on the values of those variables, or parameters to customizations (policy evaluation helper procedures) provided by each service).
IAM is loosely coupled with the namespaces of the services it serves, and that allows different services to update their authz models independently with pretty much no state or model information centralized in IAM itself. This is a key, underappreciated part of what makes AWS able to move so fast.
I can't speak for Google, but I'm working on something similar as a personal project and here is my architecture;
Each service has its own store of objects. Each store also has a directory of Metadata describing the objects contained in each service.
When you send an Auth request to a service; the service you are sending the request to looks up which service is the authority for the given object and then routes the request to that service for auth.
You can do away with the Metadata store if you offload responsibility for remembering which store to use to the user. You provide them with a cookie that tells any of your Auth servers which store contains this users data.
You can and it doesn't have to be a choke point; as far as the ACL is concerned it's just a namespace (the microservice) and an opaque ID inside that namespace.
What the Zanzibar paper describes is two big things:
(1) The auth service gives those microservices an ability to set their own inheritance rules so that you do not need to store the fullest representation of those ACLs. If you are propertly targeting the DDD “bounded context” level with one bounded context per microservice, then in theory your microservice probably defines its own authorization scopes and inheritance rules between them. (A bounded context is a business-language namespace, and it is likely that your business-level users talking about “owners” in, say, the accounting context are different than the users talking about “owners” in a documentation context—or whatever you have.) Some upfront design is probably worthwhile to make the auth service handle that, rather than giving the clients each a library implementation of half of datalog and having each operation send a dozen RPCs to the auth service for each ACL check.
(2) The microservices agree on part of a protocol to allow some eventual consistency in the mix for caching: namely, the microservices agree that their domain entities will store these opaque version numbers called zookies (that the auth service generated) whenever they are modified, and hand them to the auth service when checking later ACLs. This, the paper says, gave them an ability to do things like building indexes behind the scenes to handle request load better, without sacrificing much security. Most of the ACL operations are going to not affect your one microservice over here because they happen in a different namespace or concern different objects in the same namespace: so, I need a mechanism in my auth service
to tell me if I need an expensive query against the live data, or if I can use a cache as long as it's not too old.
This is relevant only if you have zillions of objects of hundreds of types and more such types of objects are likely to emerge in future (as you launch more products/use-case).
And you have billions of users and their sharing permission models are complex and likely to keep evolving in the future with more devices, concepts of groups/family etc.
In such a scenario, doing access control in a safe and secure way that scales and evolves well to such a large base is itself a major undertaking. You want to decouple the access control metadata from the data blob storage itself so that they each can be optimally solved for their own unique challenges and they can evolve independently too.
There is an Open Source (Go) implementation of "Zanzibar" called
Keto [0] that integrates with the rest of the Ory ecosystem. We are actually testing it and looks great so far.
This comes up every time but I think it’s worth noting that Keto provides literally none of the consistency properties of Zanzibar. All of the distributed systems homework assignments for that project have been left as TODOs.
I'm curious what's driving the resurgence in interest authorization infrastructure, particularly the Zanzibar paper. As founder of Oso (https://www.osohq.com/), I have my own opinions, and I think this is a good thing. But would love to hear others' points of view here.
My guess is that it is mainly driven by the increasing adoption of microservice (or just generally more distributed architectures). Doing fine-grained authorization in that type of architecture quite difficult and people are starting to realize that.
I think the other replies to you are probably correct, but I also can't help but think that a lot of the small/mid size businesses that use AD for Auth, have been on prem for years, and weren't really planning to make a move very soon until the Pandemic hit, have sort of run face first into the fact that they're really stuck with Microsoft now and when Azure AD goes down, their whole business tends to go with it. I don't think there's an easy solution here, but I've seen some places coming face to face with this reality and there's been some very mixed feelings and not many alternatives.
Some factors might include increasing usage of microservices, frontend SPAs, serverless, and more early startups looking to integrate with enterprises, who now have high expectations of what's possible thanks to Auth0 and the like.
I'm currently building an abstracted authorization system for PostgreSQL, and one problem I ran into were timing attacks. Granted, I only had an unoptimised prototype, but querying a table and only checking if the user has permission to read the objects after the fact led to being able to differentiate "no matching object" and "one unavailable matching object". From skimming the paper, it seems Google use this approach, why are timing attacks not a problem for them? Is it because authorization checks are so fast? Or because they make sure only to query available objects, only using Zanzibar as a final "just in case" guard?
What exactly is the attack you're worried about here?
Why do attackers have direct query access to your database? What useful information can they extract from knowing there is an unauthorized object in the database?
I'm not sure I understand the concern here. Typically there is a logged-in user, and server asks Zanzibar if the user can or cannot access some document. Whether a certain document exists or not isn't typically a secret i.e. you might get HTTP 403 (forbidden) or 404 depending on whether or not the document exists.
Maybe evening response time is some abstraction on top? It may be useful for protecting much more than just auth so it would make sense not to repeat that on every layer.
I'm just wondering if there's a one size fits all solution for authz. I spent a few days on a use case :
- users have one or several roles ( these are hierarchical )
- there are some objects in the system ( hierarchical too, eg files and folders )
- there are different features available according to a user's subscription.
I ended up with a 30 lines program which given a set of rules calculates who can access what in less than a millisecond. Does it worth an over-engineered mega system ?
The problem isn't the 30 lines, though. The problem is "millions of users, billions/trillions of objects" and both are non-hierarchical with pairwise sharing etc.
If the requirements were simple, the POSIX model would still work too :)
You are not wrong. And this pattern shows up everywhere. e.g. do you need a SaaS for "feature flags", since they're just an if statement?
In the case of authz, the argument for separating it as a concern is that many applications can share the same scheme, and you can have specialized tools for provisioning, auditing, etc.
I’m curious about what their approach is to handle consistency with object creation and deletion in the client service. ie how do clients guarantee that the relevant ACLs are created and destroyed in Zanzibar when clients create and destroy their objects.
Destroy can be done asynchronously with durable messaging but asynchronous creation of ACLs is annoying from an api consumer perspective.
Much more likely to be a reference to Brunner's classic work of dystopian fiction, which postulates that the 2010 population of Earth, projected to be around 7 billion people, could all stand shoulder to shoulder on a single island the size of Zanzibar.
The ideas (attribute based access control) have stood the test of time, but the spec is archaic, and there are relatively few implementations. You can achieve alot of what XACML was intended for with a general-purpose policy engine (OPA).
It might be. Notice that it's only been in use for about 3 years. The difference is you don't tend to upset users due to underlying infrastructure changes.
>On the fiftieth anniversary of the atrocious killing and raping of the Arabs of Zanzibar in the wake of the 1964 revolution in the Island, this paper sought to establish that this mayhem was genocide. In light of the almost complete failure to notice this tragedy, the paper pursued critical genocide studies and hidden genocide investigations to argue that this Arab tragedy in Zanzibar has been a denied genocide. Worse still, the paper showed that this genocide is commonly ignored even in studies devoted to bring to memory of hidden genocides life.
Somewhat off-topic I know, but I'd love to see this extended to some of the features that Sign in with Apple has in terms of private relay.
Signing in with Google yields (at a minimum) the e-mail address to the client which means that the list of third parties that have your e-mail (and can therefore spam you at will) is increasing exponentially. It would be great if Zanzibar extended the ACLs to include privacy controls with external services.
(Or I'm misunderstanding and this is only the component for internal Google authentication and not external federation for clients).
I can't get over the name because I definitely had a memorable experience going to Zanzibar in Toronto (https://www.yelp.ca/biz/zanzibar-toronto) shortly after turning 19.
aaronharnly|4 years ago
If so, does that become a chokepoint in a distributed microservice architecture? Or can that be avoided with an in-process or sidecar architecture in which a given microservice's objects are not separately referenced in auth persistence? If not, how do folks determine which objects to register with the auth service and which to handle independently?
jzelinskie|4 years ago
>does that become a chokepoint in a distributed microservice architecture?
It actually does the opposite because now all of your microservices can query Zanzibar at any time to get answers to authorization questions that were previously isolated to only a single application.
Full disclosure: I work on https://authzed.com (YC W21) -- a permission system as a service inspired by Zanzibar. We're also planning on doing a PapersWeLove NYC on Zanzibar in the coming months, so stay tuned!
NovemberWhiskey|4 years ago
Say your goal is to externalize just your authorization policies from your code. A simple implementation might look like an OPA sidecar to your services, with the policy itself being sourced from a separate control plane - this might be something as simple as a centrally-managed S3 bucket.
The service implementation provides the attributes to OPA to allow it to evaluate the authorization policy as part of the query. e.g. which groups is this user in, what document are they accessing, is this a read, write or delete operation.
If you want to externalize sourcing of the attributes as well, that becomes more complicated. Now you need your authorization framework to know that Bob is in "Accounting" or that quarter_end_results.xls is a document of type "Financial Results".
You can either go push or pull for attribute sourcing.
The push model is to have the relevant attribute universe delivered to each of the policy decision points, along with the policy itself. This improves static stability, as you reduce the number of real-time dependencies required for authorization queries but can be a serious data distribution and management problem - particularly if you need to be sure that data isn't going stale in some sidecar process somewhere for some reason.
The pull model is to have an attribute provider that can you can query as necessary; probably backed with an attribute cache for sanity's sake. The problems are basically the opposite set - liveness is guaranteed but static stability is more complicated.
The methods are not equivalent: in particular, the pull model is sufficient to answer simple authorization questions like 'can X do Y to Z?' - we pull the attributes of X, Y and Z and evaluate the authorization policy.
However, if you need to answer questions like 'to which Z can X do Y?', how does that work? For simple cases you may be able to iterate over the universe of Z's asking the prior question; but it generalizes poorly.
samjs|4 years ago
Depending on your requirements, yes that's kind of what happens if you want to centralise. It can make sense for Google-scale problems where you really do need to handle the complex graph of relationships between all users and resources, and doing that in any one service is non-trivial.
In practice though, a lot of service-oriented architectures can get the same benefits by having a central user management service, and keeping most of the authorization in each service. That central service can provide information like what organizations/teams/roles etc. the user belongs to, and then the individual services can make decisions based on that data.
This is the approach I covered with the hybrid approach. With this you can still implement most complex authorization models.
ak217|4 years ago
I don't know the answer for Zanzibar, but take a look at how AWS IAM solves it. IAM has very few strong opinions in its model of the world (essentially it divides the world into AWS account ID namespaces and AWS service names/namespaces, and there's not much detail beyond that). Everything else is handled through symbolic references (via string/wildcard matching) to principals, resources, and actions in the JSON policies, as well as variables in policy evaluation contexts (and conditions, which are predicates on the values of those variables, or parameters to customizations (policy evaluation helper procedures) provided by each service).
IAM is loosely coupled with the namespaces of the services it serves, and that allows different services to update their authz models independently with pretty much no state or model information centralized in IAM itself. This is a key, underappreciated part of what makes AWS able to move so fast.
zelon88|4 years ago
Each service has its own store of objects. Each store also has a directory of Metadata describing the objects contained in each service.
When you send an Auth request to a service; the service you are sending the request to looks up which service is the authority for the given object and then routes the request to that service for auth.
You can do away with the Metadata store if you offload responsibility for remembering which store to use to the user. You provide them with a cookie that tells any of your Auth servers which store contains this users data.
crdrost|4 years ago
What the Zanzibar paper describes is two big things:
(1) The auth service gives those microservices an ability to set their own inheritance rules so that you do not need to store the fullest representation of those ACLs. If you are propertly targeting the DDD “bounded context” level with one bounded context per microservice, then in theory your microservice probably defines its own authorization scopes and inheritance rules between them. (A bounded context is a business-language namespace, and it is likely that your business-level users talking about “owners” in, say, the accounting context are different than the users talking about “owners” in a documentation context—or whatever you have.) Some upfront design is probably worthwhile to make the auth service handle that, rather than giving the clients each a library implementation of half of datalog and having each operation send a dozen RPCs to the auth service for each ACL check.
(2) The microservices agree on part of a protocol to allow some eventual consistency in the mix for caching: namely, the microservices agree that their domain entities will store these opaque version numbers called zookies (that the auth service generated) whenever they are modified, and hand them to the auth service when checking later ACLs. This, the paper says, gave them an ability to do things like building indexes behind the scenes to handle request load better, without sacrificing much security. Most of the ACL operations are going to not affect your one microservice over here because they happen in a different namespace or concern different objects in the same namespace: so, I need a mechanism in my auth service to tell me if I need an expensive query against the live data, or if I can use a cache as long as it's not too old.
vinay_ys|4 years ago
And you have billions of users and their sharing permission models are complex and likely to keep evolving in the future with more devices, concepts of groups/family etc.
In such a scenario, doing access control in a safe and secure way that scales and evolves well to such a large base is itself a major undertaking. You want to decouple the access control metadata from the data blob storage itself so that they each can be optimally solved for their own unique challenges and they can evolve independently too.
kyrra|4 years ago
[0] https://news.ycombinator.com/item?id=20132520
[1] https://news.ycombinator.com/item?id=26738344
themarkers|4 years ago
https://medium.com/airbnb-engineering/himeji-a-scalable-cent...
merqurio|4 years ago
[0]: https://github.com/ory/keto
jeffbee|4 years ago
gneray|4 years ago
matthewaveryusa|4 years ago
thinkharderdev|4 years ago
ZeroCool2u|4 years ago
TechBro8615|4 years ago
etxm|4 years ago
taftster|4 years ago
https://twitter.com/LeaKissner/status/1136631437514272768
dvdkon|4 years ago
bradstewart|4 years ago
Why do attackers have direct query access to your database? What useful information can they extract from knowing there is an unauthorized object in the database?
MrKristopher|4 years ago
comboy|4 years ago
shric|4 years ago
pnocera|4 years ago
finnh|4 years ago
If the requirements were simple, the POSIX model would still work too :)
dboreham|4 years ago
In the case of authz, the argument for separating it as a concern is that many applications can share the same scheme, and you can have specialized tools for provisioning, auditing, etc.
achalshah|4 years ago
amitkanfer|4 years ago
btbuilder|4 years ago
Destroy can be done asynchronously with durable messaging but asynchronous creation of ACLs is annoying from an api consumer perspective.
stevefan1999|4 years ago
[1]: https://metalgear.fandom.com/wiki/Zanzibar_Land_Disturbance
xenophonf|4 years ago
https://en.wikipedia.org/wiki/Stand_on_Zanzibar
It's not the kind of literary allusion I'd want to make, if I were a global multinational like Google/Alphabet, but there it is.
taftster|4 years ago
https://twitter.com/LeaKissner/status/1136691523104280576
pyuser583|4 years ago
Zanzibar is an island off the coast of East Africa known for being a place where people traded cotton for enslaved humans.
Not sure the connection.
guenthert|4 years ago
skj|4 years ago
The availability guarantees necessary for basic authorization are far more strict than auditing. Auth fails closed, audit fails open.
Anything that can be stripped out of auth should be, even if we're talking about a best effort extra rpc from the auth service.
Auditing typically needs more information than auth as well, and making the auth pipe wide is a risk.
unknown|4 years ago
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KrishnaAnaril|4 years ago
ogazitt|4 years ago
SergeAx|4 years ago
sitkack|4 years ago
skj|4 years ago
1f60c|4 years ago
(maybe?)
andred14|4 years ago
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villgax|4 years ago
[deleted]
m12k|4 years ago
liotier|4 years ago
dav|4 years ago
wideareanetwork|4 years ago
throwaways885|4 years ago
Tyr42|4 years ago
aww_dang|4 years ago
https://www.researchgate.net/publication/325605315_The_1964_...
>On the fiftieth anniversary of the atrocious killing and raping of the Arabs of Zanzibar in the wake of the 1964 revolution in the Island, this paper sought to establish that this mayhem was genocide. In light of the almost complete failure to notice this tragedy, the paper pursued critical genocide studies and hidden genocide investigations to argue that this Arab tragedy in Zanzibar has been a denied genocide. Worse still, the paper showed that this genocide is commonly ignored even in studies devoted to bring to memory of hidden genocides life.
bruckie|4 years ago
headmelted|4 years ago
Signing in with Google yields (at a minimum) the e-mail address to the client which means that the list of third parties that have your e-mail (and can therefore spam you at will) is increasing exponentially. It would be great if Zanzibar extended the ACLs to include privacy controls with external services.
(Or I'm misunderstanding and this is only the component for internal Google authentication and not external federation for clients).
delroth|4 years ago
Olshansky|4 years ago