How do you delegate the ability to delegate?

Lets say you are running a large cloud (purely hypothetical here) and you want to let a user manage their own project. They are "admin" but they should be able to invite or eject people.

In order to do this, an ordinary user needs to be able to make a role assignment. However, Keystone does not support this today: if you are admin somewhere, you are admin everywhere:

Access control in OpenStack is controlled by Policy. An informal survey of operators shows that most people run with the stock policies such as the Nova policy:

In order to scope admin to the proejct, we would need to have rules that enforce this scoping: Evey rule should check that the project_id in the token provided matches the project_id of the resource of the API.

If we manage to get the policy files rewritten this way, We then need a way to limit what roles a user can assign. The default mechanism would say that a user needs to have an administrative role on the project (or domain) that they want to assign the role on.

I don't think anything I've written thus far is controversial. Then, why has it not happened yet? here are the list of problems we need to solve:

1. Operators expect the existing policy files to work as is. Changing them will break workflow. 2. If everything is scoped, we need a way to delete resources left orphan when a project is deleted from Keystone and the service does not get the notification (or know how to handle it).

Of the two, I think the top one is the more difficult to solve. Scoping everything can be handled via one of two mechanism; either allow a power-admin user to get a token scoped to some random project (even if it has been deleted) or allow a token scoped to an administrative project to also delete resources for a random project.

Dealing with the existing policy file issues is trickier, and that is the real reason for the Dynamic Policy approach: give the endpoints the ability to fetch their policy files from Keystone. If policy goes from being a configuration file to data, it is managed outside of the configuration management tools, and becomes much more fluid. This has risks, and should be an Opt-In mechanism.

Fetching the policy files from Keystone also provides the start of a richer set of management for policy rules. Currently, each of the stock policy files exists only in their seperate git repos. There is no sharing of policy rules across projects. If the policy files were managed, rule by rule, from a centralized repository, rules could be shared, providing, among other things, the ability to enforce hierarchical roles, roles namespaced to a service, and other, richer policy management.

Feedback on this approach from operators is greatly appreciated. I need to justify the effort that would go in to making this happen, so if you want it, speak up.

If, on the other hand, you feel that this is needlessly complicated or would make deployments more difficult, that is important too, and please let me know.

Finally, if you can see some alternative methods of implementing a more dynamic access control, please chime in.

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