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Policy enforcement

In this sample we'll learn how to enable policy enforcement. As the EDC are a framework, they do not provide any evaluation out-of-the-box, but instead provide an evaluation system that can be easily configured to suit custom needs. We'll perform the necessary configurations and implement and register a function for evaluating a policy.

We will set up two connectors, a provider and a consumer, and let the provider offer an asset with a policy that imposes a location restriction. So depending on the consumer's location, the consumer will be able to negotiate a contract for requesting the asset or not. The sample consists of multiple modules:

  • policy-functions: creates the provider's offer and provides the function for policy enforcement
  • [policy-enforcement-provider|consumer]: contains the build and config files for the respective connector

Creating the policy functions extension

In this extension, we'll implement and register a function to evaluate the location-restricted policy we will create later.

Creating rule bindings

In this sample, the provider will offer an asset with a policy that imposes a constraint, but if we were to run the sample now, we would not see any policy evaluation happening. This is because the EDC do not regard any rules or constraints for evaluation unless we configure it. The EDC use the concept of policy scopes to define which rules and constraints should be evaluated in certain runtime contexts, as some rules or constraints may only make sense in some contexts, but not in others. A simple example is a rule that states data must be anonymized. Evaluating this during the contract negotiation would not make much sense, as at this point in time no data is being exchanged yet and therefore nothing can be anonymized. So we need to define which rules and constraints should be evaluated in which scopes. This is done by creating rule bindings at the RuleBindingRegistry. For our example, we create the following rule bindings:

ruleBindingRegistry.bind("use", ALL_SCOPES);
ruleBindingRegistry.bind(LOCATION_CONSTRAINT_KEY, NEGOTIATION_SCOPE);

When creating a rule binding, we can bind an action type or constraint to either all scopes or just a specific one. Here, we bind the action type use to all scopes, so that rules with this action type are always evaluated. For the location constraint we choose the negotiation scope, meaning it will only be evaluated during the contract negotiation. Information on available scopes can be found here.

Implementing the function for evaluation

With the rule bindings in place, the provider will now try to evaluate our policy including the constraint during a contract negotiation, but it does not yet know how to evaluate this constraint. For this, we need to implement a function, for which the EDC offer two interfaces: AtomicConstraintFunction and RuleFunction. The former is meant for evaluating a single constraint of a rule, while is latter is meant for evaluating a complete rule node (including constraints as well as duties that may be associated with a permission). For our example, we choose to implement an AtomicConstraintFunction, as we want to evaluate our location constraint:

public class LocationConstraintFunction implements AtomicConstraintFunction<Permission> {
    
    //...
    
    @Override
    public boolean evaluate(Operator operator, Object rightValue, Permission rule, PolicyContext context) {
        var region = context.getContextData(ParticipantAgent.class).getClaims().get("region");
        
        monitor.info(format("Evaluating constraint: location %s %s", operator, rightValue.toString()));
        
        return switch (operator) {
            case EQ -> Objects.equals(region, rightValue);
            case NEQ -> !Objects.equals(region, rightValue);
            case IN -> ((Collection<?>) rightValue).contains(region);
            default -> false;
        };
    }
}

When implementing either of the function interfaces, we have to override the evaluate method. For the AtomicConstraintFunction we get the constraint's operator and right value as well as the containing rule node and a PolicyContext as parameters. Using these, we have to determine whether the constraint is fulfilled. Since we want to check the requesting participant's location, we need to access information about the participant. This is supplied through the PolicyContext. We get the participant's claim with key region to obtain information about the participant's location. We can then compare the location to the expected value depending on the operator used. The function should return true, if the constraint is fulfilled, and false otherwise.

Note: we can use the region claim here because our connectors use the iam-mock extension, which always adds a claim with this exact name to all tokens. Depending on the identity provider used, different claims may be present, or the same claim may have a different name.

Registering the function with the policy engine

After creating our function for evaluation, the last thing we need to do is register this function at the PolicyEngine, so that it is available for evaluation:

policyEngine.registerFunction(NEGOTIATION_SCOPE, Permission.class, LOCATION_CONSTRAINT_KEY, new LocationConstraintFunction(monitor));

When registering the function, we again have to specify a scope. This allows for evaluating the same rule or constraint differently in different runtime contexts. Since we bound our constraint to the negotiation scope, we also register our function for that scope. Next, we need to specify the type of rule our function should be used for. This is important, as the same constraint may have different implications as part of a permission, prohibition or duty. When registering an AtomicConstraintFunction, we also have to specify a key that the function is associated with. This has to resolve to exactly the constraint's left operand, so that the correct function for evaluation of a constraint can be chosen depending on its left operand. So we set the key to the same value we used as our constraint's left operand. And lastly, we hand over an instance of our function.

Now, during a contract negotiation, our provider will evaluate our constraint by calling our function's evaluate method.

Configuring the connectors

Next, let's configure the two connectors. For each connector we need a build file and a configuration file.

Build files

In the build file, we define the following dependencies for both connectors:

  • libs.edc.control.plane.core: the core module for the control-plane
  • libs.edc.configuration.filesystem: enables configuration via a properties file
  • libs.edc.management.api: provides the API for interacting with the control-plane
  • libs.edc.dsp: enables connector-to-connector communication via the Dataspace Protocol
  • libs.edc.iam.mock: mocks an identity provider

Note: we do not include any data-plane modules, as we are not going to transfer any data in this sample. To be able to actually transfer data, additional dependencies are required. More information can be found in the documentation and in the transfer samples.

Provider

For the provider, we also add a dependency on our previously created policy-functions extension, so that it is able to enforce a policy rule with a location constraint.

Configuration files

We create the config.properties files for both provider and consumer and first define their API bindings. We then define the DSP callback addresses, which are required for callback during the contract negotiation, as well as their participant IDs.

Consumer

For the consumer we also add the following property:

edc.mock.region=us

This defines the value for the consumer's region claim issued by the mock identity provider, which we use for evaluating the consumer's location.

Running the sample

Now, let's run the sample step by step.

1. Run connectors

First, we need to build and start both our connectors. Execute the following commands from the project root in two separate terminal windows (one per connector):

Provider:

./gradlew policy:policy-01-policy-enforcement:policy-enforcement-provider:build
java -Dedc.fs.config=policy/policy-01-policy-enforcement/policy-enforcement-provider/config.properties -jar policy/policy-01-policy-enforcement/policy-enforcement-provider/build/libs/provider.jar

Consumer:

./gradlew policy:policy-01-policy-enforcement:policy-enforcement-consumer:build
java -Dedc.fs.config=policy/policy-01-policy-enforcement/policy-enforcement-consumer/config.properties -jar policy/policy-01-policy-enforcement/policy-enforcement-consumer/build/libs/consumer.jar

2. Create the provider's offer

In order for the provider to offer any data, we need to create 3 things: an Asset (= what data should be offered), a PolicyDefinition (= under which conditions should data be offered), and a ContractDefinition, that links the Asset and PolicyDefinition.

2.1 Create the asset

We create an Asset with a DataAddress of type test. This asset will not work for a data transfer, as test is not an actual transfer type. But, as we're not going to transfer any data in this sample, this is sufficient for our example. You can view the request body for creating the asset in create-asset.json. Run the following command to create the asset:

curl -X POST -H "Content-Type: application/json" -H "X-Api-Key: password" \
  -d @policy/policy-01-policy-enforcement/resources/create-asset.json \
  "http://localhost:19193/management/v3/assets" | jq

2.2 Create the policy definition

Next. we'll create the PolicyDefinition, which contains a Policy and an ID. Each Policy needs to contain at least one rule describing which actions are allowed, disallowed or required to perform. Each rule can optionally contain a set of constraints that further refine the actions. For more information on the policy model take a look at the documentation or the policy section in the developer handbook.

For our example, we create a Permission with action type use, as we want to allow the usage of our offered data. But we only want to allow the usage under the condition that the requesting participant is in a certain location, therefore we add a constraint to our permission. In that constraint we state that the participant's location has to be equal to eu. You can view the request body for creating the policy definition in create-policy.json. Run the following command to create the policy definition:

curl -X POST -H "Content-Type: application/json" -H "X-Api-Key: password" \
  -d @policy/policy-01-policy-enforcement/resources/create-policy.json \
  "http://localhost:19193/management/v3/policydefinitions" | jq

2.3 Create the contract definition

The last thing we create is a ContractDefinition, that references the previously created policy definition and asset. We will set the policy both as the access and the contract policy in the contract definition. To read up on the difference between the two, check out the developer handbook. You can view the request body for creating the contract definition in create-contract-definition.json Run the following command to create the contract definition:

curl -X POST -H "Content-Type: application/json" -H "X-Api-Key: password" \
  -d @policy/policy-01-policy-enforcement/resources/create-contract-definition.json \
  "http://localhost:19193/management/v3/contractdefinitions" | jq

With this, the provider now offers the asset under the condition that the requesting participant is located in the EU.

3. Make a catalog request

After starting both connectors, we'll first make a catalog request from the consumer to the provider to see the provider's offers. For this, we'll use an endpoint of the consumer's management API, specifying the provider's address in the request. The request body is prepared in catalog-request.json.

curl -X POST -H "Content-Type: application/json" -H "X-Api-Key: password" \
  -d @policy/policy-01-policy-enforcement/resources/catalog-request.json \
  "http://localhost:29193/management/v3/catalog/request" | jq

We'll receive the following catalog in the response, where we can see the offer created in the provider's extension.

{
  "@id": "4462b621-fb77-4e8c-91a5-8cbd85b967c2",
  "@type": "dcat:Catalog",
  "dcat:dataset": {
    "@id": "test-document",
    "@type": "dcat:Dataset",
    "odrl:hasPolicy": {
      "@id": "MQ==:dGVzdC1kb2N1bWVudA==:NjUzNTA5M2QtYTFjMi00YTRmLWE5NjYtYTM0ZjE2NjFjOTYy",
      "@type": "odrl:Set",
      "odrl:permission": {
        "odrl:target": "test-document",
        "odrl:action": {
          "odrl:type": "use"
        },
        "odrl:constraint": {
          "odrl:leftOperand": "location",
          "odrl:operator": {
            "@id": "odrl:eq"
          },
          "odrl:rightOperand": "eu"
        }
      },
      "odrl:prohibition": [],
      "odrl:obligation": [],
      "odrl:target": {
        "@id": "test-document"
      }
    },
    "dcat:distribution": [],
    "id": "test-document"
  },
  "dcat:service": {
    "@id": "fe9581ee-b4ec-473c-b0b7-96f30d957e87",
    "@type": "dcat:DataService",
    "dct:terms": "connector",
    "dct:endpointUrl": "http://localhost:8282/protocol"
  },
  "participantId": "provider",
  "@context": {
    "@vocab": "https://w3id.org/edc/v0.0.1/ns/",
    "edc": "https://w3id.org/edc/v0.0.1/ns/",
    "dcat": "https://www.w3.org/ns/dcat/",
    "dct": "https://purl.org/dc/terms/",
    "odrl": "http://www.w3.org/ns/odrl/2/",
    "dspace": "https://w3id.org/dspace/v0.8/"
  }
}

But why are we able to see this offer, even though we set the location restricted policy as the access policy and our consumer is not in the EU? While we did set the restricted policy as the access policy, we only bound the constraint to the NEGOTIATION_SCOPE using the RuleBindingRegistry, meaning it will not be regarded for evaluations in the cataloging phase.

We can now use the offer details received in the catalog to start a contract negotiation with the provider.

4. Start a contract negotiation

To start the contract negotiation between provider and consumer, we'll use an endpoint of the consumer's management API. In the request body for this request, we need to provide information about which connector we want to negotiate with, which protocol to use and which offer we want to negotiate. The request body is prepared in contractoffer.json. To start the negotiation, run the following command:

curl -X POST -H "Content-Type: application/json" -H "X-Api-Key: password" \
  -d @policy/policy-01-policy-enforcement/resources/contract-request.json \
  "http://localhost:29193/management/v3/contractnegotiations" | jq

You'll get back a UUID. This is the ID of the contract negotiation process which is being asynchronously executed in the background.

5. Get the contract negotiation state

Using the ID received in the previous step, we can now view the state of the negotiation by calling another endpoint of the consumer's management API:

curl -X GET -H "X-Api-Key: password" "http://localhost:29193/management/v3/contractnegotiations/<UUID>" | jq

In the response we'll get a description of the negotiation, similar to the following:

{
  ...
  "edc:contractAgreementId": null,
  "edc:state": "TERMINATED",
  ...
}

We can see that the negotiation has been declined, and we did not receive a contract agreement. If we now take a look at the provider's logs, we'll see the following lines:

INFO 2024-02-12T11:07:32.954014912 Evaluating constraint: location EQ eu
DEBUG 2024-02-12T11:07:32.9562391 [Provider] Contract offer rejected as invalid: Policy eu-policy not fulfilled

The consumer was not able to get a contract agreement, because it does not fulfil the location-restricted policy. This means we have successfully implemented and configured the policy evaluation on provider side. Building up on this example, you can now tackle more complex policies, by e.g. defining and combining different constraints and creating the respective functions for evaluation.

Sample variations

You can play around with this sample a bit and run it in different variations, yielding different outcomes. Some possible variations are described in the following.

Note: the following variations do not build up on each other, so make sure to revert any changes done for one variation before proceeding with the next!

Set consumer region to eu

Our policy requires the consumer to be in the EU. Change the property edc.mock.region in the consumer's config.properties to the value eu and run the sample again. This time, the negotiation will reach the state FINALIZED and reference a contract agreement, as our consumer now fulfils the policy.

edc.mock.region=eu

Remove binding of constraint

In our PolicyFunctionsExtension, we've created a rule binding so that our constraint would be evaluated during the contract negotiation. Remove this binding and run the sample again (while leaving the consumer's property edc.mock-region with value us!). The negotiation will be confirmed and reference a contract agreement, even though our consumer is not in the correct location. This happens, as without the binding of the constraint, the provider will not regard it during evaluation.

ruleBindingRegistry.bind("use", ALL_SCOPES);
//ruleBindingRegistry.bind(LOCATION_CONSTRAINT_KEY, NEGOTIATION_SCOPE);

Remove binding of action type

In our PolicyFunctionsExtension, we've created rule bindings for our permission's action type as well as the constraint. In the previous variation, we've removed the binding for the constraint. For this variation, we want to leave the binding for the constraint in place, and instead remove the binding for the action type. Run the sample again (while leaving the consumer's property edc.mock-region with value us!) and you will see the negotiation being confirmed. Even though the constraint is bound to be evaluated and the consumer does not fulfil it, the constraint is not evaluated and our function never called. This happens because there is no rule binding for the permission containing the constraint, and thus the whole permission node is disregarded during evaluation.

//ruleBindingRegistry.bind("use", ALL_SCOPES);
ruleBindingRegistry.bind(LOCATION_CONSTRAINT_KEY, NEGOTIATION_SCOPE);

Bind the constraint to the cataloging scope

In our example, we've bound the constraint to the NEGOTIATION_SCOPE. Let's remove this binding and instead bind the constraint as well as our function to the CATALOGING_SCOPE and rebuild the provider. When running a sample again, you will not see the offer in the provider's catalog anymore. As the constraint is now evaluated during cataloging, the offer is filtered out because our consumer does not fulfil the location constraint. Since the request body for the negotiation is already prepared, you can still try to initiate a negotiation. Even though the constraint is not bound to the negotiation scope anymore, the negotiation will be terminated. When receiving a request for a negotiation, the provider will still evaluate its contract definitions' access policies using the catalog scope, to ensure that a consumer cannot negotiate an offer it is not allowed to see.

ruleBindingRegistry.bind(LOCATION_CONSTRAINT_KEY, CATALOGING_SCOPE);
policyEngine.registerFunction(CATALOGING_SCOPE, Permission.class, LOCATION_CONSTRAINT_KEY, new LocationConstraintFunction(monitor));