This thread is a continuation of a discussion started by @pospi and David Hand to discuss how to use the capabilities API and what the best patterns for access control, governance and delegated authority are in Holochain apps.
The original thread: https://chat.holochain.org/appsup/channels/dev-capabilities
Sharing the key comments to bring visibility to the topic.
From @pospi: I think @david-hand was planning on leading the fact-finding we need for this at the moment, but to start perhaps a summary of our current thinking to pull apart & discuss is the most worthwhile thing:
A common use-case in REA networks is to have application-specific behaviour in other modules coded to respond to different types of AgentRelationships. For example, a Person who is a member of an Organisation may have special privileges that non-members do not.
This module deals with People, Organisations and recording the AgentRelationships between different entities- nothing further. Having a separate collaboration space to record this information allows for organisational structures to be shared with other modules without the logic for managing such structures needing to be replicated in each module. It may be accessed via other modules to perform access checks; though it is more likely that such access checks would reference the local Holochain capability register rather than data in other modules.
The expected parameters needed to allow for delegated authority are detailed in this Github issue but the details are pending decisions to be made by the HDK core team.
We probably want this module to orchestrate permissions and bridging for agents who join & leave managed groups, and filter those permissions down through the connected / deployed networks via way of capability grants. In implementing this we may want a split- one zome for the governance processes & agent relationships, another for applying REA-specific capabilities to the rest of the network. The latter would be reusable with other governance frameworks, the former would not. Capabilities (and access control logic) are always local to each module- to modules other than agent relationships, the agents who interact with them are all just anonymous people who happen to have permission to do certain things.
^referenced GH issue: https://github.com/holo-rea/holo-rea/issues/9
Related, more direct questions:
From David-Hand: What I would like to know is as follows:
Thanks for initiating this thread @dhtnetwork.
@pospi weāve been thinking about this too for our interchange. Correct me if you think itās not related.
We need to keep a record of which apps the users have āstaked their reputationā into. This is important because it gives the user read access (and in some cases write access) to information in other DNAs. The easy option is to record this table within our DNA, but we think it might be possible to keep this record in the manner you have described above.
@pospi I forget exactly where that conversation left off, and how old it was. I presume you have more questions about capability tokens, cross-DNA privileges, and how a set of modules like HoloREA could use those primitives ā if so, ask away!
Hint: for now it seems like a capability grant/claim is just a pattern thatās embodied in a special data structure with some convenience functions to make it easier to operate on it. I think the reason for this is that it was originally a low-level feature that got exposed in the HDK because it could be useful for app devs. My hunch is that you will want to take our pattern of cap tokens and reimplement it in a way that serves your needs ā partly because cap grants/claims are private entries that donāt get published to the DHT. Iām learning that, in proper capability-based security, the agent granting access to a resource must have full control over it. For Holochain this means that capability claims are exercised by asking the grantor to perform an action for you. In multi-agent environments where the DNA can ātrigger eventsā this doesnāt hold in the same way, although I still think itās true that you could design somethingā¦ perhaps you donāt have any one agent strictly controlling access to the resource, but you do have the DNA and the DHT enforcing how resource access is exercised. Would be a productive/fun topic to get into, and it would help inform my documentation writing too!
This sounds accurate 
The more I dive into CBAC the more I see it as the elegant general-purpose solution to access control in distributed systems. I think @thedavidmeister shares that opinion; indeed heās the main one who sold me on this.
So what weāre thinking in terms of capabilities mainly relates to how you implement RBAC (roles) on top of CBAC (capabilities); at a technical level weāre pretty sure itās about grouping sets of capabilities into roles to lessen configuration overhead.
We think thereās probably need for a use-case specific ārole configurationā mechanism that groups might want to author on their own; coupled with a general-purpose capability mapping zome and/or library. Short version-
We probably want this [RBAC] module to orchestrate permissions and bridging for agents who join & leave managed groups, and filter those permissions down through the connected / deployed networks via way of capability grants.
What level of abstraction do we think this lives at? Is facilitating group management functionality part of Holochainās core app infrastructure, or something to be done on a per-project basis?
Iām never sure what belongs in core-land vs library-land ā sometimes I think CRUD and even source chains shouldāve stayed out of core and been part of the HDK instead 
When I learned about our implementation of capability-based security, and how basically all that weāve opened up (so far) is sugar around committing capability grants/claims, I thought, āhm, we could do so much more with this concept!ā But it grew out of the need to enforce access restrictions on zome calls, and it shows that heritage in the fact that the grant entries are always private. What if we enforced capabilities at the validation level as well as the agent level?
Iāve been chewing on a general-purpose application of the pattern to publicly enforced privileges in How to do validation on a custom function of a module? - #2 by pauldaoust Imagine the implementation described there, only with a lot fewer built-in assumptions and more generic params. Something likeā¦
pub struct PublicCapabilityBody<T> {
// Optional -- if None, anyone holding the token may make the claim, which
// might be the wrong thing to do when all grants are public on the DHT.
subject: Option<Address>,
// Application-specific.
terms: T
}
// This is kind of like a certificate.
pub struct PublicCapability<T> {
body: PublicCapabilityBody<T>,
authorization: holochain_core_types::signature::Provenance
}
Then your terms T could be anything you like:
PublicCapability). Expiry date is important because validation functions shouldnāt be checking the current state of the DHT, so all the information needed for determining the validity of the entry should be supplied at validation time (either by embedding it in the entry, committing it as a previous entry and supplying it as part of a validation package, or specifying it as a validation dependency (not supported yet)).Can you tell I like composition? It may be better, for the purpose of developer ergonomics, to bake in a bunch of assumptions about what developers will want in their terms:
public struct PublicCapabilityBody<T> {
subject: Option<Address>,
resource: Option<Address>,
expiry: Option<DateTime>,
extra_terms: T
}
The thing Iām having a hard time wrapping my mind around is that true capability-based security depends on one component having completely control over a resource and mediating access to it through the token and nothing more. In a distributed system where the controller of a resource may be offline for a long time, what does ācontrol of a resourceā mean? The DHT itself can enforce whether an action is valid or not, but it canāt control a resource that everybody knows about. Maybe capability-based security is the wrong pattern for this use case, and we need to reframe this as some sort of portable, certificate-based proof of privileges. Sort of like the W3Cās Verifiable Claims, which has some very very agent-centric language.
@pauldaoust because it isnāt a resource that everybody knows about if it is private behind a cap token?
@thedavidmeister yeah, thatās the problem Iām struggling with ā is it possible to take the concept of capability tokens (control of a resource + access granted via a token) and somehow project it into a public sphere? My current thoughts are (a) no, but (b) collectively-enforced use of collectively-granted use of collectively-held resources (in other words, verifiable claims + validation rules) can have some similar data structures and solve the same need to govern resource access. Maybe we need new patterns with new names. I feel like Elinor Ostromās work could inform us here.
@pauldaoust iām not 100% sure what problem youāre trying to solve, is it data availability for things sitting behind a capability?
@thedavidmeister more about a general pattern for controlling access to public things (which for Holochain means write access to the DHT). Iām thinking out loud, so my thoughts probably seem scattered as my understanding evolves.
My criteria, assumptions, and understanding of the problem space so far:
To my mind, the only thing that can satisfy the criteria given my assumptions is some sort of portable, verifiable claim/credential. This would look like a certificate signed by the agent who has authority to grant a particular privilege. More thoughts:
@pauldaoust i did some work with @philipbeadle around a JWT style analogy that could go somewhere near revocation by bridging into a deepkey DHT
this still only controls writes through an expiry model, either against a trusted source of timestamps or āthis token allows up to N writes before you need to get a new oneā
this is about writes tied to an authenticated identity rather than a key, against some other system, it might cover some of what youāre reaching for but not all
the thing is that if you start putting arbitrary logic on reads then monitoring network health would become (i think) infinitely difficult as per the design intent of rrDHT
i donāt know how youād enforce such a security model eitherā¦ you can revoke access to new things but not things that already exist in the public space
my gut is that youāre better off controlling who can join the network and open/maintain connections using membranes (could be token based) and slicing your DHTs along the lines of who should be participating with that public data within that network, than deliberately creating āsub-DHTsā within a single network
is there a specific use case you have in mind that breaks this model?
Not necessarily, Iām in that dangerous territory of considering possibilities without specific use cases.
To clarify, Iām not interested in solving read access ā as you say, membranes are the right place to control that sort of thing. When I referred to the inability to control read access, I just meant that it wouldnāt be sufficient to control write access to something simply by hoping that nobody would discover its hash, because everyone can eventually read everything.
It sounds like youāre saying that itād be much simpler to control write access by controlling who can join the DHT, than implementing some sort of privileges system within the DHT. Fair enough, and I think thatās probably true for most applications.
Actually, I am thinking about a use case where you would want to have different privileges in a DHTā¦ there are probably many others, but this one is salient because it relates to HoloREA.
Suppose I participate in a co-op. Within our little co-op DHT, all of us have permission to do whatever we like. But in interfacing with the outside world, only some of us have the authority to represent the co-op. And those people may leave the org and new ones may replace them.
So now letās consider a global marketplace DHT. Those who are purchasing from / selling to me have to know that I have the right to represent the co-op. So in that global marketplace, the co-op has a record that makes its entity-ness known to the world, signed by its founders. This record indicates that anyone presuming to represent the co-op must carry a claim with them that has the signature of at least one of the founders, either directly or as part of a chain of claims.
I read a bit about JWT, and it sounds like theyāre very similar to W3C Verifiable Claims/Credentials ā in fact, you can format a VC as a JWT. So it sounds like weāre on the same page there (and thatās probably because I got the idea from you, many months ago). It strikes me that itās not that different from an SSL cert too ā itās just a cryptographically signed way of communicating that some authority recognises some other entity and claims that they should have the right to do such-and-such a thing.
I did notice that JWT payloads are encrypted, though, which wouldnāt work for this use case because the details of the claim needs to be readable in order to be validated.
@pauldaoust JWE payloads are encrypted while JWT are just base64 and plaintext
even more, the JWT spec allows to specify the alg used to sign, so we were looking at whether we could specify the deepkey-compatible DNA used to be the identity provider
this is all authentication though, on top of which authorization can be built
this all sounds exactly like what @philipbeadle is working on right now
this has nothing to do with capabilities though
thatās about protecting access to semi-private data
that needs to sit with the owner of the data because once something becomes shared, the network needs to monitor its health in an agent centric way
i have no idea how youād build efficient heuristics to monitor the health of data that you donāt know who is allowed to see it, until after you interact with them directly 1:1 and then run a function that may or may not be time sensitiveā¦
so yeah:
identity tokens for internal and external authentications 
capability logic for semi-private owned data
slicing DHTs across membrane/access boundaries
trying to create sub-DHTs on the fly 
oh yeah, youāre right ā just base64. Thatās what I get for skimming!
Sounds like Iām gonna have to talk to @philipbeadle some more!
When you say āsemi-privateā do you mean private source chain entries that I share through N2N messaging after you present a valid claim? I thought capabilities were meant as a primitive to facilitate this sort of thing, around which app devs build all the communication logic.
oh! Curious to hear why thatās a ā is it starting to feel like an anti-pattern?
ah. got it. Re: on-the-fly sub-DHTs, my thinking was that the UI could just call admin/dna/install_from_file and pass a param (maybe a UUID, maybe a property) that would fork the DNA into a separate space. Then it would call all the admin functions to create/start an instance from that new DNA and bind it to an interface, etc. Then of course the UI would be responsible for handling all the flow between instances; you canāt set up a conductor bridge at runtime, can you? I canāt imagine how it would be possible, because the DNA would have to know about the bridge at compile time, and also you might have many mini-spaces to bridge to (thinking of private chat channels for instance).
Membrane control could involve passing a "progenitor" key/value into install_from_file that contains the public key of the root authority that signs all the claims that people bring with them. Thisāll only work when weāre able to put arbitrary data (such as the aforementioned claims) into the agent ID entry though, because validate_agent is what creates the membrane.
Anyhow, thatās the plan Iāve mapped out for the tutorial that accompanies my Core Concepts article on āSpawning new DNA instances from a templateā (not yet written). Let me know if you think this is wacky or bad 
@pauldaoust thatās something different again, thatās not a āsub-DHTā building new apps from templates is still very much a complete, standalone DHT with its own network health heuristics and validation, etc.
the bit you canāt do is within a single DHT say āsome of you get this set of data and some of you get this other set of dataā, outside the standard neighbourhood logic
Oh, I get it. Thought you meant sub-DHT as the many forked-mini-DHTs pattern weāve already established. The SSB folks are working on something that would control propagation (or at least visibility) of data using double ratchets and tangles, but thatās not something I think we should think about supporting.
Anyhow, Iām tempted to delete my previous post because I think it takes away from the conversation at hand. Mind if I do that and delete your follow-up as well?
@pauldaoust i think itās nice to continue the train of thought
i kind of like how messy the forums are, feels very organic
Creating new DHTs and joining new DHTs is on my roadmap for Hylo. When you create a new Community it will created new DHts for Community, Post, Comments. My current issue is managing the instanceID so the UI knows which DHT to be calling.