coder/coderd/rbac

Authz

Package rbac implements Role-Based Access Control for Coder.

See USAGE.md for a hands-on approach to using this package.

Overview

Authorization defines what permission a subject has to perform actions to objects:

• Permission is binary: yes (allowed) or no (denied).
• Subject in this case is anything that implements interface rbac.Subject.
• Action here is an enumerated list of actions. Actions can differ for each object type. They typically read like, Create, Read, Update, Delete, etc.
• Object here is anything that implements rbac.Object.

Permission Structure

A permission is a rule that grants or denies access for a subject to perform an action on a object. A permission is always applied at a given level:

• site level applies to all objects in a given Coder deployment.
• org level applies to all objects that have an organization owner (org_owner)
• user level applies to all objects that have an owner with the same ID as the subject.

Permissions at a higher level always override permissions at a lower level.

The effect of a permission can be:

• positive (allows)
• negative (denies)
• abstain (neither allows or denies, not applicable)

Negative permissions always override positive permissions at the same level. Both negative and positive permissions override abstain at the same level.

This can be represented by the following truth table, where Y represents positive, N represents negative, and _ represents abstain:

Action	Positive	Negative	Result
read	Y	_	Y
read	Y	N	N
read	_	_	_
read	_	N	N

Permission Representation

Permissions are represented in string format as <sign>?<level>.<object>.<id>.<action>, where:

• negated can be either + or -. If it is omitted, sign is assumed to be +.
• level is either site, org, or user.
• object is any valid resource type.
• id is any valid UUID v4.
• id is included in the permission syntax, however only scopes may use id to specify a specific object.
• action is typically create, read, modify, delete, but you can define other verbs as needed.

Example Permissions

• +site.app.*.read: allowed to perform the read action against all objects of type app in a given Coder deployment.
• -user.workspace.*.create: user is not allowed to create workspaces.

Roles

A role is a set of permissions. When evaluating a role's permission to form an action, all the relevant permissions for the role are combined at each level. Permissions at a higher level override permissions at a lower level.

The following table shows the per-level role evaluation. Y indicates that the role provides positive permissions, N indicates the role provides negative permissions, and indicates the role does not provide positive or negative permissions. YN indicates that the value in the cell does not matter for the access result.

Role (example)	Site	Org	User	Result
site-admin	Y	YN_	YN_	Y
no-permission	N	YN_	YN_	N
org-admin	_	Y	YN_	Y
non-org-member	_	N	YN_	N
user	_	_	Y	Y
	_	_	N	N
unauthenticated	_	_	_	N

Scopes

Scopes can restrict a given set of permissions. The format of a scope matches a role with the addition of a list of resource ids. For a authorization call to be successful, the subject's roles and the subject's scopes must both allow the action. This means the resulting permissions is the intersection of the subject's roles and the subject's scopes.

An example to give a readonly token is to grant a readonly scope across all resources +site.*.*.read. The intersection with the user's permissions will be the readonly set of their permissions.

Resource IDs

There exists use cases that require specifying a specific resource. If resource IDs are allowed in the roles, then there is an unbounded set of resource IDs that be added to an "allow_list", as the number of roles a user can have is unbounded. This also adds a level of complexity to the role evaluation logic that has large costs at scale.

The use case for specifying this type of permission in a role is limited, and does not justify the extra cost. To solve this for the remaining cases (eg. workspace agent tokens), we can apply an allow_list on a scope. For most cases, the allow_list will just be ["*"] which means the scope is allowed to be applied to any resource. This adds negligible cost to the role evaluation logic and 0 cost to partial evaluations.

Example of a scope for a workspace agent token, using an allow_list containing a single resource id.

    "scope": {
      "name": "workspace_agent",
      "display_name": "Workspace_Agent",
      // The ID of the given workspace the agent token correlates to.
      "allow_list": ["10d03e62-7703-4df5-a358-4f76577d4e2f"],
      "site": [/* ... perms ... */],
      "org": {/* ... perms ... */},
      "user": [/* ... perms ... */]
    }

OPA (Open Policy Agent)

Open Policy Agent (OPA) is an open source tool used to define and enforce policies. Policies are written in a high-level, declarative language called Rego. Coder’s RBAC rules are defined in the policy.rego file under the authz package.

When OPA evaluates policies, it binds input data to a global variable called input. In the rbac package, this structured data is defined as JSON and contains the action, object and subject (see regoInputValue in astvalue.go). OPA evaluates whether the subject is allowed to perform the action on the object across three levels: site, org, and user. This is determined by the final rule allow, which aggregates the results of multiple rules to decide if the user has the necessary permissions. Similarly to the input, OPA produces structured output data, which includes the allow variable as part of the evaluation result. Authorization succeeds only if allow explicitly evaluates to true. If no allow is returned, it is considered unauthorized. To learn more about OPA and Rego, see https://www.openpolicyagent.org/docs.

Application and Database Integration

• rbac/authz.go – Application layer integration: provides the core authorization logic that integrates with Rego for policy evaluation.
• database/dbauthz/dbauthz.go – Database layer integration: wraps the database layer with authorization checks to enforce access control.

There are two types of evaluation in OPA:

• Full evaluation: Produces a decision that can be enforced. This is the default evaluation mode, where OPA evaluates the policy using input data that contains all known values and returns output data with the allow variable.
• Partial evaluation: Produces a new policy that can be evaluated later when the unknowns become known. This is an optimization in OPA where it evaluates as much of the policy as possible without resolving expressions that depend on unknown values from the input. To learn more about partial evaluation, see this OPA blog post.

Application of Full and Partial evaluation in rbac package:

• Full Evaluation is handled by the RegoAuthorizer.Authorize() method in authz.go. This method determines whether a subject (user) can perform a specific action on an object. It performs a full evaluation of the Rego policy, which returns the allow variable to decide whether access is granted (true) or denied (false or undefined).
• Partial Evaluation is handled by the RegoAuthorizer.Prepare() method in authz.go. This method compiles OPA’s partial evaluation queries into SQL WHERE clauses. These clauses are then used to enforce authorization directly in database queries, rather than in application code.

Authorization Patterns:

• Fetch-then-authorize: an object is first retrieved from the database, and a single authorization check is performed using full evaluation via Authorize().
• Authorize-while-fetching: Partial evaluation via Prepare() is used to inject SQL filters directly into queries, allowing efficient authorization of many objects of the same type. dbauthz methods that enforce authorization directly in the SQL query are prefixed with Authorized, for example, GetAuthorizedWorkspaces.

Testing

• OPA Playground: https://play.openpolicyagent.org/
• OPA CLI (opa eval): useful for experimenting with different inputs and understanding how the policy behaves under various conditions. opa eval returns the constraints that must be satisfied for a rule to evaluate to true.
  • opa eval requires an input.json file containing the input data to run the policy against. You can generate this file using the gen_input.go script. Note: the script currently produces a fixed input. You may need to tweak it for your specific use case.

Full Evaluation

opa eval --format=pretty "data.authz.allow" -d policy.rego -i input.json

This command fully evaluates the policy in the policy.rego file using the input data from input.json, and returns the result of the allow variable:

• data.authz.allow accesses the allow rule within the authz package.
• data.authz on its own would return the entire output object of the package.

This command answers the question: “Is the user allowed?”

Partial Evaluation

opa eval --partial --format=pretty 'data.authz.allow' -d policy.rego --unknowns input.object.owner --unknowns input.object.org_owner --unknowns input.object.acl_user_list --unknowns input.object.acl_group_list -i input.json

This command performs a partial evaluation of the policy, specifying a set of unknown input parameters. The result is a set of partial queries that can be converted into SQL WHERE clauses and injected into SQL queries.

This command answers the question: “What conditions must be met for the user to be allowed?”

Benchmarking

Benchmark tests to evaluate the performance of full and partial evaluation can be found in authz_test.go. You can run these tests with the -bench flag, for example:

go test -bench=BenchmarkRBACFilter -run=^$

To capture memory and CPU profiles, use the following flags:

• -memprofile memprofile.out
• -cpuprofile cpuprofile.out

The script benchmark_authz.sh runs the authz benchmark tests on the current Git branch or compares benchmark results between two branches using benchstat. benchstat compares the performance of a baseline benchmark against a new benchmark result and highlights any statistically significant differences.

• To run benchmark on the current branch:

  benchmark_authz.sh --single
  

• To compare benchmarks between 2 branches:

  benchmark_authz.sh --compare main prebuild_policy