Use Access Grants to Access Resources

AccessGrantSession

The inrupt-client-accessgrant module provides an AccessGrantSession that builds an authenticated Session object using both:

• an OpenID-based session and

• one or more access grants.

Then, a SolidClient/SolidSyncClient can use this session to access resources using the approved access grant(s).

Continuing the example from Create Access Requests/Grants, ExamplePrinter backend server, with the appropriate access grants, can access the resources for printing.

For convenience, ExamplePrinter’s backend server’s code to instantiate AccessGrantClient for ExamplePrinter is repeated here:

public class ExamplePrinterRequestingClass {

   private final URI PS_ACCESS_GRANT_URI = URI.create("https://vc.inrupt.com");
   private Session session;  // Session for ExamplePrinter.
   // ... Logic to initialize the ExamplePrinter's session has been omitted for brevity.

   private final AccessGrantClient accessgrantClient = new AccessGrantClient(PS_ACCESS_GRANT_URI)
         .session(session);

   // ...
   // ...

}

1. Get the Access Grant(s) to Use

The user can only access those access grants where the user is the creator of the access grant (i.e., the grantor) or the recipient of the access grant (i.e., the grantee). That is, the ESS’ Access Grant service only returns those access grants where the user is the creator or the recipient.

Fetch a Specific Access Grant

If the Access Grant’s id is known, the application can directly retrieve the access grant using AccessGrantClient.fetch with the Access Grant’s id.

The fetch operation can return expired or future access grants.

// String grantID = "https://vc.{ESS DOMAIN}/vc/xxxxxx...";
AccessGrant accessGrant = accessgrantClient.fetch(URI.create(grantID), AccessGrant.class)
      .toCompletableFuture()
      .join();

Query for Access Grants

The application can use AccessGrantClient.query to query for active (i.e., current and not expired) access grants. To use AccessGrantClient.query for access grants, you can pass in a CredentialFilter object CredentialFilter<AccessGrant> that specifies the query filter values (i.e., a combination of the resource, creator, recipient, purpose, and type).

You can use CredentialFilter.Builder and its methods to build a CredentialFilter for access grants:

Method	Descriptions
.status	Optional. Include a credential status in the query object. The following values are supported for access grants: ACTIVE when used with AccessGrant queries, this returns all active access grants: those that have not expired and have not been revoked. EXPIRED when used with AccessGrant queries, this returns all access grants that have expired. REVOKED when used with AccessGrant queries, this returns all access grants that have been revoked by the resource owner.
.fromAgent	Optional. Include the creator of the access grant in the query filter. This is the resource owner.
.toAgent	Optional. Include the recipient of the access grant in the query filter. This is the agent that is granted access. In the example, the value is the ExamplePrinter’s WebID https://id.example.com/examplePrinter.
.resource	Optional. Include the resource in the query object. Use this filter to return access grants bound to a specific resource.
.purpose	Optional. Include a purpose in the query object. Use this filter to return access grants bound to a specific purpose.
.issuedWithin	Optional. Include a time constraint on the issuance date in the query object. All matched credentials will have been issued within the provided duration value. Certain time constraints are available for use with this method, including: P1D One day P7D Seven days P1M One month P3M Three months
.revokedWithin	Optional. Include a time constraint on the revocation date in the query object. All matched credentials will have been revoked within the provided duration value. Certain time constraints are available for use with this method, including: P1D One day P7D Seven days P1M One month P3M Three months
.build	Builds the CredentialFilter object. To build a query object for access grants (i.e., CredentialFilter<AccessGrant>), specify the class AccessGrant.class to the .build method.

The following example queries for active access grants, given to ExamplePrinter, that provide access for a specific resource for the purpose of photo printing. Specifically,

1. The example uses the CredentialFilter.Builder and its methods to:

   • Specify the resource .resource(...), the purpose .purpose(...), and the status .status(CredentialStatus.ACTIVE), and

   • Build .build(AccessGrant.class) a CredentialFilter<AccessGrant>.

2. Calls AccessGrantClient.query with the built CredentialFilter<AccessGrant> object.

   CredentialFilter<AccessGrant> accessGrantFilter = CredentialFilter
       .newBuilder()
       .status(CredentialFilter.CredentialStatus.ACTIVE)
       .resource(URI.create("https://storage.example.com/some/resource"))
       .purpose(URI.create("https://purpose.example.com/PhotoPrinting"))
       .build(AccessGrant.class);
   
   CredentialResult<AccessGrant> result = accessgrantClient
       .query(accessGrantFilter)
       .toCompletableFuture().join();

3. Navigate through the response CredentialResult object.

List<AccessGrant> items = result.getItems();

if (result.nextPage().isPresent()) {
    CredentialResult<AccessGrant> page2 = agClientForUser
        .query(result.nextPage().get())
        .toCompletableFuture().join();
}

From the list, the agent can select the access grant to use.

2. Create an AccessGrantSession

To instantiate an AccessGrantSession, call the constructor with the following parmeters:

• OpenID-based session

• Access Grants to Use

For example, the following code instantiates an AccessGrantSession using both the ExamplePrinter’s OpenID Session and the access grant:

Session agSession = AccessGrantSession.ofAccessGrant(session, accessGrant);

3. Create a Solid Client

To access the resource with access grants, create a SolidSyncClient or SolidClient using the AccessGrantSession:

SolidSyncClient client = SolidSyncClient.getClient().session(agSession);

4. Access the Resource

Use the SolidSyncClient.send() method to access the non-RDF resources and SolidSyncClient.read() method to read RDF resources.

For example, the following code uses the client associated with ExamplePrinter and the access grants to read the image file (a Non-RDF resource) at the resource URL:

SolidNonRDFSource resource = client.read(URI.create("https://storage.example.com/some/resource"), SolidNonRDFSource.class).toCompletableFuture().join();

If you receive an HTTP 403 Forbidden error, check that you have enabled the use of access grants for the resource.