Compare `this` with `ctx.subject`

[fracek]

Preflight checklist

• I could not find a solution in the existing issues, docs, nor discussions.
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Describe your problem

I'm using Keto to implement permission for my SaaS-like product. Users can interact with it through a cli program (using a personal access token) or directly from the website (with session cookies). PATs can be "admin" tokens or "view" tokens, only "admin" tokens can make changes to the account. I implemented the following partial OPL policy:

class AccessToken implements Namespace {
}

class Account implements Namespace {
  related: {
    token: AccessToken[]
    admin_token: AccessToken[]
  }

  permits = {
    edit: (ctx: Context): boolean =>
      // this == ctx ||
      this.related.admin_token.includes(ctx.subject),

    view: (ctx: Context): boolean =>
        this.permits.edit(ctx) ||
        this.related.token.includes(ctx.subject),
  }
}

What's missing is a way to add the tuple Account:alice#edit@Account:alice.

Describe your ideal solution

My ideal solution is to add a permission check like this == ctx.subject.

Workarounds or alternatives

Add a editor relation from Account to Account and check that this.related.editor.includes(ctx.subject).

Version

v0.10.0-alpha.0

Additional Context

No response

[zepatrik]

From the way we write this.related.token.includes(ctx.subject) I think we should make the syntax either this == ctx.subject or this.equals(ctx.subject).
The workaround is valid but obviously cumbersome and not really necessary.

[hperl]

If we implement this, then the this == ctx.subject call should not hit the database. Then, it would be beneficial to have a special syntax for this.

On the syntax itself, I'm not sure if this == ctx.subject or this.equals(ctx.subject) are already clear enough to convey what is happening.

From an implementation point of view, this would require:

• adding support for this expression in the OPL parser
• adding a new userset rewrites type (maybe SubjectEqualsObject), and attach it to the relation if we parsed the expression
• implement the SubjectEqualsObject rewrite in the check engine (simple, just compare object and subject for a given relation tuple)

Of course, add tests to make sure your change was effective, and run the fuzzers if you touch parser code.

[github-actions]

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[beanow-at-crabnebula]

Thanks stale bot! I'm also subscribing to this issue.

Agreeing with the part where ideally this avoids hitting the database.

If we implement this, then the this == ctx.subject call should not hit the database. Then, it would be beneficial to have a special syntax for this.

My current workaround for this, is that our client library wrapping Keto calls is responsible for doing this comparison.
While that works, it would be even better if we can opt-in to this behavior using OPL. Keeps authorization logic in one place.

[BenjaminNolan]

This would massively simplify our namespace definitions and make working with Keto a lot nicer than it already is. :) If you need a hand with testing or reviewing this, I'd be happy to help and give feedback if needed. I note there's some discussion about this on Slack in January (just within the 90-day cut-off!) and February, but I can't see any further follow-ups since then, hence chiming in here. :)