feat: Add support for agentGroup ACL rules

Co-Authored-By: Ludovico Granata <Ludogranata@gmail.com>

src/authorization/access-checkers/AgentGroupAccessChecker.ts

@@ -0,0 +1,50 @@
+import type { Term } from 'n3';
+import type { ResourceIdentifier } from '../../ldp/representation/ResourceIdentifier';
+import type { RepresentationConverter } from '../../storage/conversion/RepresentationConverter';
+import { fetchDataset } from '../../util/FetchUtil';
+import { promiseSome } from '../../util/PromiseUtil';
+import { readableToQuads } from '../../util/StreamUtil';
+import { ACL, VCARD } from '../../util/Vocabularies';
+import type { AccessCheckerArgs } from './AccessChecker';
+import { AccessChecker } from './AccessChecker';
+
+/**
+ * Checks if the given WebID belongs to a group that has access.
+ * Implements the behaviour of groups from the WAC specification.
+ */
+export class AgentGroupAccessChecker extends AccessChecker {
+  private readonly converter: RepresentationConverter;
+
+  public constructor(converter: RepresentationConverter) {
+    super();
+    this.converter = converter;
+  }
+
+  public async handle({ acl, rule, credentials }: AccessCheckerArgs): Promise<boolean> {
+    if (typeof credentials.webId === 'string') {
+      const { webId } = credentials;
+      const groups = acl.getObjects(rule, ACL.terms.agentGroup, null);
+
+      return await promiseSome(groups.map(async(group: Term): Promise<boolean> =>
+        this.isMemberOfGroup(webId, group)));
+    }
+    return false;
+  }
+
+  /**
+   * Checks if the given agent is member of a given vCard group.
+   * @param webId - WebID of the agent that needs access.
+   * @param group - URL of the vCard group that needs to be checked.
+   *
+   * @returns If the agent is member of the given vCard group.
+   */
+  private async isMemberOfGroup(webId: string, group: Term): Promise<boolean> {
+    const groupDocument: ResourceIdentifier = { path: /^[^#]*/u.exec(group.value)![0] };
+
+    // Fetch the required vCard group file
+    const dataset = await fetchDataset(groupDocument.path, this.converter);
+
+    const quads = await readableToQuads(dataset.data);
+    return quads.countQuads(group, VCARD.terms.hasMember, webId, null) !== 0;
+  }
+}