policy

README

Policy Service

This project has been migrated to Eclipse Foundation, and it can be found under https://gitlab.eclipse.org/eclipse/xfsc/

The policy service provides HTTP API to evaluate/execute OPA policies.

It is developed using the Goa v3 framework and uses the Go OPA framework as a library.

Swagger OpenAPI documentation

In the local docker-compose environment, the Swagger URL is available at http://localhost:8081/swagger-ui/

High-level Overview

flowchart LR
	A([client]) -- HTTP --> B[Policy API]
	subgraph policy
		B --> C[(policies DB)]
	end
	C --sync--- D[Git Server]

Policy Evaluation

The policy service exposes HTTP endpoints to evaluate/execute policies. The endpoint interface is conformant to the TSA requirements document.

To evaluate a policy a GET or POST request is sent to the evaluation URL. The example URL below is given for the local docker-compose environment. The host and port parts will be different for the different environments.

# URL with example policy repository, group, name and version
http://localhost:8081/policy/policies/xfsc/didresolve/1.0/evaluation

# URL with parameter placeholders
http://localhost:8081/policy/{repository}/{group}/{policy}/{version}/evaluation

There are four parameters in the URL specifying which exact policy should be evaluated - repository, group, policy and version. These parameters are also important during policy development (see below) as group and policy must be used as package name inside the policy source code file.

The body of the POST request can be empty, but if it's not empty, it must be JSON. It is passed directly to the policy execution runtime. Inside the policy it is accessed with the global variable name input. For example, if you pass to the evaluation endpoint the following JSON, it will be accessible by input.message:

{
  "message": "hello world"
}

Here is a complete example CURL request:

curl -X POST http://localhost:8081/policy/policies/xfsc/didresolve/1.0/evaluation -d '{"message":"hello world"}'

Policy Locking

The service exposes HTTP endpoints to lock and unlock policies. Locking a policy means that it's not allowed for evaluation (execution). Unlocking a policy allows its evaluation/execution to proceed normally.

Lock a policy with POST request:

curl -X POST http://localhost:8081/policy/policies/xfsc/didresolve/1.0/lock

Unlock a policy with DELETE request:

curl -X DELETE http://localhost:8081/policy/policies/xfsc/didresolve/1.0/lock

Policy Bundles

A policy bundle contains a Policy source code, static data, configuration and some additional meta-info necessary for verifying the origin of the policy (who signed the bundle).

The service allows to export a policy bundle by making HTTP request against a policy URL of the same format as is used for evaluation, but instead of using the evaluation word at the end, you replace it with export. That will pack the policy as ZIP bundle, and the ZIP bundle will be returned to the client.

wget http://localhost:8081/repository/policy/xfsc/didresolve/1.0/export

See here for more detailed overview of policy bundles export/import.

Policy Storage

Policies (rego source code and metadata) are stored in a storage, which is an interface and different implementations could be used. You can check the interface here.

Currently, there are two implementations of the storage interface:

• MongoDB
• Memory

Matrix for storage feature availability:

Feature	MongoDB	Memory
Policy Lock/Unlock	Yes	Yes*
Change Notifications	Yes	Yes*
Storage extension functions	Yes	Yes*
Automatic synchronization	Yes	N/A
Bundle import/export	Yes	Yes*

* Functionality is available only for the current instance of the policy service. Synchronization between instances of the policy service is not available.

In order to use another storage technology, one should implement the Storage interface.

flowchart LR
	A[Policy\nDeveloper] --git push/merge--> B[Git branch]
	subgraph Git Server
		B --> C[example/1.0/policy.rego]
		B --> D[example/2.0/policy.rego]
		B --> G[example/3.0/policy.rego]
	end
	C --> E[Sync]
	D --> E[Sync]
	G --> E[Sync]
	E --update--> F
	subgraph policy service
		F[(policies DB)]
	end

Policy Development

• Policy Extensions Functions

Policies are written in the Rego language. Please refer to the OPA documentation for detailed overview of Rego and OPA capabilities.

Some conventions must be followed when writing policies.

1. The filename of the policy must follow rules for the naming and directory structure: the group, policy name and version are directories inside the Git repo and policy file must be named policy.rego. For example: /xfsc/example/1.0/policy.rego.
2. In the same directory there could be a data file containing static JSON, which is automatically available for use during policy evaluation by using the data variable. The file must be named data.json. Example: /xfsc/example/1.0/data.json
3. In the same directory there could be a configuration file containing information for getting static JSON data from external URL. The file must be named data-config.json. Example: /xfsc/example/1.0/data-config.json

Note that there should only be one of the two files data.json or data-config.json in the same directory. If both files exist in the same directory tha data from the data.json file will be eventually overwritten by the data acquired using the configuration from the data-config.json file. 4. In the same directory there could be a configuration file containing JSON schema for validating the policy evaluation output. The file must be named output-schema.json. Example: /xfsc/example/1.0/output-schema.json 5. The policy package name inside the policy source code file must exactly match the group and policy (name) of the policy.

What does it mean?

• Let's see an example for the 1st convention.

package xfsc.example

allow {
    input.message == "hello world"
}

Next, the filename must be /xfsc/example/1.0/policy.rego. When such file is synchronized with the policy service (storage), the naming convention allows the service to understand which part is the policy group, which part is policy name and which part is version.

If we create the above policy and store it in the Git repo as /xfsc/example/1.0/policy.rego, after the Git server is synchronized with the Policy Storage, the policy service will automatically expose URLs for working with the policy at:

http://localhost:8081/policy/xfsc/example/1.0/evaluation
http://localhost:8081/policy/xfsc/example/1.0/lock

• The 2nd rule for static data file naming is to make sure that file /xfsc/example/1.0/data.json is passed and is available to the evaluation runtime when a policy is evaluated at URL:

http://localhost:8081/policy/xfsc/example/1.0/evaluation

Static data is accessed within the Rego policy with data.someKey. Example: If the /xfsc/example/1.0/data.json file is:

{
  "name": "some name"
}

one could access the data using data.name within the Rego source code.

• The 3rd rule for configuration file is to provide configurations for getting static JSON data from external URL. The file must contain a URL, an HTTP method and a period, after which an HTTP request is made to get the latest data.

The period must be added as duration e.g. 10h, 1h30m etc.

The file MAY contain body for the request. Example file contents:

{
  "url": "http://example.com/data.json?page=3",
  "method": "GET",
  "period": "10h",
  "body": {
    "key": "value"
  }
}

This means that every 10 hours an HTTP request is going to be made on the given URL, with GET method and the result is going to be stored as static data for this policy and passed during evaluation.

• The 4th rule for policy output schema validation is to provide a JSON schema which will be used to validate the output of the policy.

Example file contents:

{
  "type": "object",
  "properties": {
    "foo": {
      "type": "string",
      "minLength": 5
    }
  }
}

This policy output would be valid: {"foo":"barbaz"}. This policy output would be invalid: {"foo":"bar"}.

• The 5th rule for package naming is needed so that a generic evaluation function can be mapped and used for evaluating all kinds of different policies. Without a package naming rule, there's no way the service can automatically generate HTTP endpoints for working with arbitrary dynamically uploaded policies.

Access HTTP Headers inside a policy

HTTP request headers are passed to the evaluation runtime on each request. They can be accessed through a built-in extension function named external.http.header(). It accepts as argument the name of the header in Canonical format. For example, inside Rego the value of a header named Authorization can be retrieved as follows:

package example.example

auth := external.http.header("Authorization")

Header names are passed to the Rego runtime in Canonical format. This means that the first character and any characters following a hyphen are uppercase and the rest are lowercase.

More examples, if the policy service receive a request with the following headers:

accept-encoding: gzip, deflate
Accept-Language: en-us
fOO: Bar
x-loCATion: Baz

Inside a policy these headers could be accessed as follows:

accept_encoding := external.http.header("Accept-Encoding")
accept_language := external.http.header("Accept-Language")
foo := external.http.header("Foo")
location := external.http.header("X-Location")

Policy Extensions Functions

A brief documentation for the available Rego extensions functions which can be used during policy development.

Policy Extensions Functions

You can also look at the source code in package regofunc to understand the inner-working and capabilities of the extension functions.

GDPR

GDPR

Dependencies

Dependencies

License

Apache 2.0 license