feat: Split WebAclReader behaviour over multiple classes

src/authorization/ParentContainerReader.ts

@@ -0,0 +1,115 @@
+import type { CredentialGroup } from '../authentication/Credentials';
+import type { ResourceIdentifier } from '../http/representation/ResourceIdentifier';
+import { getLoggerFor } from '../logging/LogUtil';
+import type { IdentifierStrategy } from '../util/identifiers/IdentifierStrategy';
+import { IdentifierMap, IdentifierSetMultiMap } from '../util/map/IdentifierMap';
+import type { MapEntry } from '../util/map/MapUtil';
+import { modify } from '../util/map/MapUtil';
+import type { PermissionReaderInput } from './PermissionReader';
+import { PermissionReader } from './PermissionReader';
+import type { PermissionMap, Permission, PermissionSet, AccessMap } from './permissions/Permissions';
+import { AccessMode } from './permissions/Permissions';
+
+/**
+ * Determines `delete` and `create` permissions for those resources that need it
+ * by making sure the parent container has the required permissions.
+ *
+ * Create requires `append` permissions on the parent container.
+ * Delete requires `write` permissions on both the parent container and the resource itself.
+ */
+export class ParentContainerReader extends PermissionReader {
+  protected readonly logger = getLoggerFor(this);
+
+  private readonly reader: PermissionReader;
+  private readonly identifierStrategy: IdentifierStrategy;
+
+  public constructor(reader: PermissionReader, identifierStrategy: IdentifierStrategy) {
+    super();
+    this.reader = reader;
+    this.identifierStrategy = identifierStrategy;
+  }
+
+  public async handle({ requestedModes, credentials }: PermissionReaderInput): Promise<PermissionMap> {
+    // Finds the entries for which we require parent container permissions
+    const containerMap = this.findParents(requestedModes);
+
+    // Merges the necessary parent container modes with the already requested modes
+    const combinedModes = modify(new IdentifierSetMultiMap(requestedModes), { add: containerMap.values() });
+    const result = await this.reader.handleSafe({ requestedModes: combinedModes, credentials });
+
+    // Updates the create/delete permissions based on the parent container permissions
+    for (const [ identifier, [ container ]] of containerMap) {
+      this.logger.debug(`Determining ${identifier.path} create and delete permissions based on ${container.path}`);
+      result.set(identifier, this.addContainerPermissions(result.get(identifier), result.get(container)));
+    }
+    return result;
+  }
+
+  /**
+   * Finds the identifiers for which we need parent permissions.
+   * Values are the parent identifier and the permissions they need.
+   */
+  private findParents(requestedModes: AccessMap): IdentifierMap<MapEntry<AccessMap>> {
+    const containerMap = new IdentifierMap<[ResourceIdentifier, Set<AccessMode>]>();
+    for (const [ identifier, modes ] of requestedModes.entrySets()) {
+      if (modes.has(AccessMode.create) || modes.has(AccessMode.delete)) {
+        const container = this.identifierStrategy.getParentContainer(identifier);
+        containerMap.set(identifier, [ container, this.getParentModes(modes) ]);
+      }
+    }
+    return containerMap;
+  }
+
+  /**
+   * Determines which permissions are required on the parent container.
+   */
+  private getParentModes(modes: ReadonlySet<AccessMode>): Set<AccessMode> {
+    const containerModes: Set<AccessMode> = new Set();
+    if (modes.has(AccessMode.create)) {
+      containerModes.add(AccessMode.append);
+    }
+    if (modes.has(AccessMode.delete)) {
+      containerModes.add(AccessMode.write);
+    }
+    return containerModes;
+  }
+
+  /**
+   * Merges the container permission set into the resource permission set
+   * based on the parent container rules for create/delete permissions.
+   */
+  private addContainerPermissions(resourceSet?: PermissionSet, containerSet?: PermissionSet): PermissionSet {
+    resourceSet = resourceSet ?? {};
+    containerSet = containerSet ?? {};
+    // Already copying the `permissionSet` here since the loop only iterates over the container entries.
+    // It is possible `resourceSet` contains a key that `containerSet` does not contain.
+    const resultSet: PermissionSet = { ...resourceSet };
+    for (const [ group, containerPermission ] of Object.entries(containerSet) as [ CredentialGroup, Permission ][]) {
+      resultSet[group] = this.interpretContainerPermission(resourceSet[group] ?? {}, containerPermission);
+    }
+    return resultSet;
+  }
+
+  /**
+   * Determines the create and delete permissions for the given resource permissions
+   * based on those of its parent container.
+   */
+  private interpretContainerPermission(resourcePermission: Permission, containerPermission: Permission): Permission {
+    const mergedPermission = { ...resourcePermission };
+
+    // https://solidproject.org/TR/2021/wac-20210711:
+    // When an operation requests to create a resource as a member of a container resource,
+    // the server MUST match an Authorization allowing the acl:Append or acl:Write access privilege
+    // on the container for new members.
+    mergedPermission.create = containerPermission.append && resourcePermission.create !== false;
+
+    // https://solidproject.org/TR/2021/wac-20210711:
+    // When an operation requests to delete a resource,
+    // the server MUST match Authorizations allowing the acl:Write access privilege
+    // on the resource and the containing container.
+    mergedPermission.delete = resourcePermission.write && containerPermission.write &&
+      resourcePermission.delete !== false;
+
+    return mergedPermission;
+  }
+}

src/authorization/WebAclAuxiliaryReader.ts

@@ -0,0 +1,76 @@
+import type { CredentialGroup } from '../authentication/Credentials';
+import type { AuxiliaryStrategy } from '../http/auxiliary/AuxiliaryStrategy';
+import type { ResourceIdentifier } from '../http/representation/ResourceIdentifier';
+import { getLoggerFor } from '../logging/LogUtil';
+import { IdentifierSetMultiMap } from '../util/map/IdentifierMap';
+import type { MapEntry } from '../util/map/MapUtil';
+import { modify } from '../util/map/MapUtil';
+import type { PermissionReaderInput } from './PermissionReader';
+import { PermissionReader } from './PermissionReader';
+import { AclMode } from './permissions/AclPermission';
+import type { AclPermission } from './permissions/AclPermission';
+import type { AccessMap, AccessMode, PermissionMap, PermissionSet } from './permissions/Permissions';
+
+/**
+ * Determines the permission for ACL auxiliary resources.
+ * This is done by looking for control permissions on the subject resource.
+ */
+export class WebAclAuxiliaryReader extends PermissionReader {
+  protected readonly logger = getLoggerFor(this);
+
+  private readonly reader: PermissionReader;
+  private readonly aclStrategy: AuxiliaryStrategy;
+
+  public constructor(reader: PermissionReader, aclStrategy: AuxiliaryStrategy) {
+    super();
+    this.reader = reader;
+    this.aclStrategy = aclStrategy;
+  }
+
+  public async handle({ requestedModes, credentials }: PermissionReaderInput): Promise<PermissionMap> {
+    // Finds all the ACL identifiers
+    const aclMap = new Map(this.findAcl(requestedModes));
+
+    // Replaces the ACL identifies with the corresponding subject identifiers
+    const updatedMap = modify(new IdentifierSetMultiMap(requestedModes),
+      { add: aclMap.values(), remove: aclMap.keys() });
+    const result = await this.reader.handleSafe({ requestedModes: updatedMap, credentials });
+
+    // Extracts the ACL permissions based on the subject control permissions
+    for (const [ identifier, [ subject ]] of aclMap) {
+      this.logger.debug(`Mapping ${subject.path} control permission to all permissions for ${identifier.path}`);
+      result.set(identifier, this.interpretControl(identifier, result.get(subject)));
+    }
+    return result;
+  }
+
+  /**
+   * Finds all ACL identifiers and maps them to their subject identifier and the requested modes.
+   */
+  private* findAcl(accessMap: AccessMap): Iterable<[ResourceIdentifier, MapEntry<AccessMap>]> {
+    for (const [ identifier ] of accessMap) {
+      if (this.aclStrategy.isAuxiliaryIdentifier(identifier)) {
+        const subject = this.aclStrategy.getSubjectIdentifier(identifier);
+        // Unfortunately there is no enum inheritance so we have to cast like this
+        yield [ identifier, [ subject, new Set([ AclMode.control ] as unknown as AccessMode[]) ]];
+      }
+    }
+  }
+
+  /**
+   * Updates the permissions for an ACL resource by interpreting the Control access mode as allowing full access.
+   */
+  protected interpretControl(identifier: ResourceIdentifier, permissionSet: PermissionSet = {}): PermissionSet {
+    const aclSet: PermissionSet = {};
+    for (const [ group, permissions ] of Object.entries(permissionSet) as [ CredentialGroup, AclPermission ][]) {
+      const { control } = permissions;
+      aclSet[group] = {
+        read: control,
+        append: control,
+        write: control,
+        control,
+      } as AclPermission;
+    }
+    return aclSet;
+  }
+}

src/authorization/WebAclReader.ts

@@ -4,13 +4,14 @@ import { CredentialGroup } from '../authentication/Credentials';
 import type { AuxiliaryIdentifierStrategy } from '../http/auxiliary/AuxiliaryIdentifierStrategy';
 import type { ResourceIdentifier } from '../http/representation/ResourceIdentifier';
 import { getLoggerFor } from '../logging/LogUtil';
+import type { ResourceSet } from '../storage/ResourceSet';
 import type { ResourceStore } from '../storage/ResourceStore';
 import { INTERNAL_QUADS } from '../util/ContentTypes';
 import { createErrorMessage } from '../util/errors/ErrorUtil';
 import { ForbiddenHttpError } from '../util/errors/ForbiddenHttpError';
 import { InternalServerError } from '../util/errors/InternalServerError';
-import { NotFoundHttpError } from '../util/errors/NotFoundHttpError';
 import type { IdentifierStrategy } from '../util/identifiers/IdentifierStrategy';
+import { IdentifierMap, IdentifierSetMultiMap } from '../util/map/IdentifierMap';
 import { readableToQuads } from '../util/StreamUtil';
 import { ACL, RDF } from '../util/Vocabularies';
 import type { AccessChecker } from './access/AccessChecker';
@@ -18,7 +19,7 @@ import type { PermissionReaderInput } from './PermissionReader';
 import { PermissionReader } from './PermissionReader';
 import type { AclPermission } from './permissions/AclPermission';
 import { AclMode } from './permissions/AclPermission';
-import type { PermissionSet } from './permissions/Permissions';
+import type { PermissionMap } from './permissions/Permissions';
 import { AccessMode } from './permissions/Permissions';
 
 // Maps WebACL-specific modes to generic access modes.
@@ -29,24 +30,27 @@ const modesMap: Record<string, Readonly<(keyof AclPermission)[]>> = {
   [ACL.Control]: [ AclMode.control ],
 } as const;
 
-type AclSet = { targetAcl: Store; parentAcl?: Store };
-
 /**
- * Handles permissions according to the WAC specification.
+ * Finds the permissions of a resource as defined in the corresponding ACL resource.
+ * Does not make any deductions such as checking parent containers for create permissions
+ * or applying control permissions for ACL resources.
+ *
  * Specific access checks are done by the provided {@link AccessChecker}.
  */
 export class WebAclReader extends PermissionReader {
   protected readonly logger = getLoggerFor(this);
 
   private readonly aclStrategy: AuxiliaryIdentifierStrategy;
+  private readonly resourceSet: ResourceSet;
   private readonly aclStore: ResourceStore;
   private readonly identifierStrategy: IdentifierStrategy;
   private readonly accessChecker: AccessChecker;
 
-  public constructor(aclStrategy: AuxiliaryIdentifierStrategy, aclStore: ResourceStore,
+  public constructor(aclStrategy: AuxiliaryIdentifierStrategy, resourceSet: ResourceSet, aclStore: ResourceStore,
     identifierStrategy: IdentifierStrategy, accessChecker: AccessChecker) {
     super();
     this.aclStrategy = aclStrategy;
+    this.resourceSet = resourceSet;
     this.aclStore = aclStore;
     this.identifierStrategy = identifierStrategy;
     this.accessChecker = accessChecker;
@@ -57,79 +61,57 @@ export class WebAclReader extends PermissionReader {
    * Will throw an error if this is not the case.
    * @param input - Relevant data needed to check if access can be granted.
    */
-  public async handle({ identifier, credentials, modes }: PermissionReaderInput):
-  Promise<PermissionSet> {
+  public async handle({ credentials, requestedModes }: PermissionReaderInput): Promise<PermissionMap> {
     // Determine the required access modes
-    this.logger.debug(`Retrieving permissions of ${credentials.agent?.webId} for ${identifier.path}`);
-
-    const isAclResource = this.aclStrategy.isAuxiliaryIdentifier(identifier);
-    const mainIdentifier = isAclResource ? this.aclStrategy.getSubjectIdentifier(identifier) : identifier;
-
-    // Adding or removing resources changes the container listing
-    const requiresContainerCheck = modes.has(AccessMode.create) || modes.has(AccessMode.delete);
-
-    // Rather than restricting the search to only the required modes,
-    // we collect all modes in order to have complete metadata (for instance, for the WAC-Allow header).
-    const acl = await this.getAcl(mainIdentifier, requiresContainerCheck);
-    const permissions = await this.findPermissions(acl.targetAcl, credentials, isAclResource);
-
-    if (requiresContainerCheck) {
-      this.logger.debug(`Determining ${identifier.path} permissions requires verifying parent container permissions`);
-      const parentPermissions = acl.targetAcl === acl.parentAcl ?
-        permissions :
-        await this.findPermissions(acl.parentAcl!, credentials, false);
-
-      // https://solidproject.org/TR/2021/wac-20210711:
-      // When an operation requests to create a resource as a member of a container resource,
-      // the server MUST match an Authorization allowing the acl:Append or acl:Write access privilege
-      // on the container for new members.
-      permissions[CredentialGroup.agent]!.create = parentPermissions[CredentialGroup.agent]!.append;
-      permissions[CredentialGroup.public]!.create = parentPermissions[CredentialGroup.public]!.append;
-
-      // https://solidproject.org/TR/2021/wac-20210711:
-      // When an operation requests to delete a resource,
-      // the server MUST match Authorizations allowing the acl:Write access privilege
-      // on the resource and the containing container.
-      permissions[CredentialGroup.agent]!.delete =
-        permissions[CredentialGroup.agent]!.write && parentPermissions[CredentialGroup.agent]!.write;
-      permissions[CredentialGroup.public]!.delete =
-        permissions[CredentialGroup.public]!.write && parentPermissions[CredentialGroup.public]!.write;
-    }
-    return permissions;
+    this.logger.debug(`Retrieving permissions of ${credentials.agent?.webId ?? 'an unknown agent'}`);
+    const aclMap = await this.getAclMatches(requestedModes.distinctKeys());
+    const storeMap = await this.findAuthorizationStatements(aclMap);
+    return await this.findPermissions(storeMap, credentials);
   }
 
   /**
    * Finds the permissions in the provided WebACL quads.
-   * @param acl - Store containing all relevant authorization triples.
+   *
+   * Rather than restricting the search to only the required modes,
+   * we collect all modes in order to have complete metadata (for instance, for the WAC-Allow header).
+   *
+   * @param aclMap - A map containing stores of ACL data linked to their relevant identifiers.
    * @param credentials - Credentials to check permissions for.
-   * @param isAcl - If the target resource is an acl document.
    */
-  private async findPermissions(acl: Store, credentials: CredentialSet, isAcl: boolean): Promise<PermissionSet> {
-    const publicPermissions = await this.determinePermissions(acl, credentials.public);
-    const agentPermissions = await this.determinePermissions(acl, credentials.agent);
+  private async findPermissions(aclMap: Map<Store, ResourceIdentifier[]>, credentials: CredentialSet):
+  Promise<PermissionMap> {
+    const result: PermissionMap = new IdentifierMap();
+    for (const [ store, aclIdentifiers ] of aclMap) {
+      // WebACL only supports public and agent permissions
+      const publicPermissions = await this.determinePermissions(store, credentials.public);
+      const agentPermissions = await this.determinePermissions(store, credentials.agent);
+      for (const identifier of aclIdentifiers) {
+        result.set(identifier, {
+          [CredentialGroup.public]: publicPermissions,
+          [CredentialGroup.agent]: agentPermissions,
+        });
+      }
+    }
 
-    return {
-      [CredentialGroup.agent]: this.updateAclPermissions(agentPermissions, isAcl),
-      [CredentialGroup.public]: this.updateAclPermissions(publicPermissions, isAcl),
-    };
+    return result;
   }
 
   /**
    * Determines the available permissions for the given credentials.
    * Will deny all permissions if credentials are not defined
    * @param acl - Store containing all relevant authorization triples.
-   * @param credentials - Credentials to find the permissions for.
+   * @param credential - Credentials to find the permissions for.
    */
-  private async determinePermissions(acl: Store, credentials?: Credential): Promise<AclPermission> {
+  private async determinePermissions(acl: Store, credential?: Credential): Promise<AclPermission> {
     const aclPermissions: AclPermission = {};
-    if (!credentials) {
+    if (!credential) {
       return aclPermissions;
     }
 
     // Apply all ACL rules
     const aclRules = acl.getSubjects(RDF.type, ACL.Authorization, null);
     for (const rule of aclRules) {
-      const hasAccess = await this.accessChecker.handleSafe({ acl, rule, credential: credentials });
+      const hasAccess = await this.accessChecker.handleSafe({ acl, rule, credential });
       if (hasAccess) {
         // Set all allowed modes to true
         const modes = acl.getObjects(rule, ACL.mode, null);
@@ -147,122 +129,101 @@ export class WebAclReader extends PermissionReader {
   }
 
   /**
-   * Sets the correct values for non-acl permissions such as create and delete.
-   * Also adds the correct values to indicate that having control permission
-   * implies having read/write/etc. on the acl resource.
+   * Finds the ACL data relevant for all the given resources.
+   * The input set will be modified in place.
    *
-   * The main reason for keeping the control value is so we can correctly set the WAC-Allow header later.
+   * @param targets - Targets to find ACL data for.
+   *
+   * @returns A map linking ACL resources to the relevant identifiers.
    */
-  private updateAclPermissions(aclPermissions: AclPermission, isAcl: boolean): AclPermission {
-    if (isAcl) {
-      return {
-        read: aclPermissions.control,
-        append: aclPermissions.control,
-        write: aclPermissions.control,
-        create: aclPermissions.control,
-        delete: aclPermissions.control,
-        control: aclPermissions.control,
-      };
+  private async getAclMatches(targets: Iterable<ResourceIdentifier>):
+  Promise<IdentifierSetMultiMap<ResourceIdentifier>> {
+    const aclMap = new IdentifierSetMultiMap<ResourceIdentifier>();
+
+    for (const target of targets) {
+      this.logger.debug(`Searching ACL data for ${target.path}`);
+      const aclIdentifier = await this.getAclRecursive(target);
+      aclMap.add(aclIdentifier, target);
     }
-    return {
-      ...aclPermissions,
-      create: aclPermissions.write,
-      delete: aclPermissions.write,
-    };
+
+    return aclMap;
   }
 
   /**
-   * Finds the ACL data relevant for its resource, and potentially its parent if required.
-   * All quads in the resulting store(s) can be interpreted as being relevant ACL rules for their target.
+   * Finds the ACL document relevant for the given identifier,
+   * following the steps defined in https://solidproject.org/TR/2021/wac-20210711#effective-acl-resource.
    *
-   * @param target - Target to find ACL data for.
-   * @param includeParent - If parent ACL data is also needed.
+   * @param identifier - {@link ResourceIdentifier} of which we need the ACL document.
    *
-   * @returns The relevant triples.
+   * @returns The {@link ResourceIdentifier} of the relevant ACL document.
    */
-  private async getAcl(target: ResourceIdentifier, includeParent: boolean): Promise<AclSet> {
-    this.logger.debug(`Searching ACL data for ${target.path}${includeParent ? 'and its parent' : ''}`);
-    const to = includeParent ? this.identifierStrategy.getParentContainer(target) : target;
-    const acl = await this.getAclRecursive(target, to);
-
-    // The only possible case where `acl` has 2 values instead of 1
-    // is when the `target` has an acl, and `includeParent` is true.
-    const keys = Object.keys(acl);
-    if (keys.length === 2) {
-      const result: AclSet = { targetAcl: await this.filterStore(acl[target.path], target.path, true) };
-      // The other key will be the parent
-      const parentKey = keys.find((key): boolean => key !== target.path)!;
-      result.parentAcl = await this.filterStore(acl[parentKey], parentKey, parentKey === to.path);
-
-      return result;
-    }
-
-    // Only 1 key: no parent was requested, target had no direct acl resource, or both
-    const [ path, store ] = Object.entries(acl)[0];
-    const result: AclSet = { targetAcl: await this.filterStore(store, path, path === target.path) };
-    if (includeParent) {
-      // In case the path is not the parent, it will also just use the defaults just like the target
-      result.parentAcl = path === to.path ? await this.filterStore(store, path, true) : result.targetAcl;
-    }
-
-    return result;
-  }
-
-  /**
-   * Finds the ACL resources from all resources in the path between the two (inclusive) identifiers.
-   * It is important that `from` is a child path of `to`, otherwise behaviour is undefined.
-   *
-   * The result is a key/value object with the keys being the identifiers of resources in the path
-   * that had a corresponding ACL resource, and the value being the contents of that ACL resource.
-   *
-   * The function stops after it finds an ACL resource relevant for the `to` identifier.
-   * This is either its corresponding ACL resource, or one if its parent containers if such a resource does not exist.
-   *
-   * Rethrows any non-NotFoundHttpErrors thrown by the ResourceStore.
-   * @param from - First resource in the path for which ACL data is needed.
-   * @param to - Last resource in the path for which ACL data is needed.
-   *
-   * @returns A map with the key being the actual identifier of which the ACL was found
-   * and a list of all data found within.
-   */
-  private async getAclRecursive(from: ResourceIdentifier, to: ResourceIdentifier): Promise<Record<string, Store>> {
+  private async getAclRecursive(identifier: ResourceIdentifier): Promise<ResourceIdentifier> {
     // Obtain the direct ACL document for the resource, if it exists
-    this.logger.debug(`Trying to read the direct ACL document of ${from.path}`);
-    const result: Record<string, Store> = {};
-    try {
-      const acl = this.aclStrategy.getAuxiliaryIdentifier(from);
-      this.logger.debug(`Trying to read the ACL document ${acl.path}`);
-      const data = await this.aclStore.getRepresentation(acl, { type: { [INTERNAL_QUADS]: 1 }});
-      this.logger.info(`Reading ACL statements from ${acl.path}`);
+    this.logger.debug(`Trying to read the direct ACL document of ${identifier.path}`);
 
-      result[from.path] = await readableToQuads(data.data);
+    const acl = this.aclStrategy.getAuxiliaryIdentifier(identifier);
+    this.logger.debug(`Determining existence of  ${acl.path}`);
+    if (await this.resourceSet.hasResource(acl)) {
+      this.logger.info(`Found applicable ACL document ${acl.path}`);
+      return acl;
+    }
+    this.logger.debug(`No direct ACL document found for ${identifier.path}`);
 
-      if (from.path.length <= to.path.length) {
-        return result;
-      }
-    } catch (error: unknown) {
-      if (NotFoundHttpError.isInstance(error)) {
-        this.logger.debug(`No direct ACL document found for ${from.path}`);
-      } else {
-        const message = `Error reading ACL for ${from.path}: ${createErrorMessage(error)}`;
+    // Find the applicable ACL document of the parent container
+    this.logger.debug(`Traversing to the parent of ${identifier.path}`);
+    if (this.identifierStrategy.isRootContainer(identifier)) {
+      this.logger.error(`No ACL document found for root container ${identifier.path}`);
+      // https://solidproject.org/TR/2021/wac-20210711#acl-resource-representation
+      // The root container MUST have an ACL resource with a representation.
+      throw new ForbiddenHttpError('No ACL document found for root container');
+    }
+    const parent = this.identifierStrategy.getParentContainer(identifier);
+    return this.getAclRecursive(parent);
+  }
+
+  /**
+   * For every ACL/identifier combination it finds the relevant ACL triples for that identifier.
+   * This is done in such a way that store results are reused for all matching identifiers.
+   * The split is based on the `acl:accessTo` and `acl:default` triples.
+   *
+   * @param map - Map of matches that need to be filtered.
+   */
+  private async findAuthorizationStatements(map: IdentifierSetMultiMap<ResourceIdentifier>):
+  Promise<Map<Store, ResourceIdentifier[]>> {
+    // For every found ACL document, filter out triples that match for specific identifiers
+    const result = new Map<Store, ResourceIdentifier[]>();
+    for (const [ aclIdentifier, matchedTargets ] of map.entrySets()) {
+      const subject = this.aclStrategy.getSubjectIdentifier(aclIdentifier);
+      this.logger.debug(`Trying to read the ACL document ${aclIdentifier.path}`);
+      let contents: Store;
+      try {
+        const data = await this.aclStore.getRepresentation(aclIdentifier, { type: { [INTERNAL_QUADS]: 1 }});
+        contents = await readableToQuads(data.data);
+      } catch (error: unknown) {
+        // Something is wrong with the server if we can't read the resource
+        const message = `Error reading ACL resource ${aclIdentifier.path}: ${createErrorMessage(error)}`;
         this.logger.error(message);
         throw new InternalServerError(message, { cause: error });
       }
-    }
 
-    // Obtain the applicable ACL of the parent container
-    this.logger.debug(`Traversing to the parent of ${from.path}`);
-    if (this.identifierStrategy.isRootContainer(from)) {
-      this.logger.error(`No ACL document found for root container ${from.path}`);
-      // Solid, §10.1: "In the event that a server can’t apply an ACL to a resource, it MUST deny access."
-      // https://solid.github.io/specification/protocol#web-access-control
-      throw new ForbiddenHttpError('No ACL document found for root container');
+      // SubjectIdentifiers are those that match the subject identifier of the found ACL document (so max 1).
+      // Due to how the effective ACL document is found, all other identifiers must be (transitive) children.
+      // This has impact on whether the `acl:accessTo` or `acl:default` predicate needs to be checked.
+      const subjectIdentifiers: ResourceIdentifier[] = [];
+      const childIdentifiers: ResourceIdentifier[] = [];
+      for (const target of matchedTargets) {
+        (target.path === subject.path ? subjectIdentifiers : childIdentifiers).push(target);
+      }
+      if (subjectIdentifiers.length > 0) {
+        const subjectStore = await this.filterStore(contents, subject.path, true);
+        result.set(subjectStore, subjectIdentifiers);
+      }
+      if (childIdentifiers.length > 0) {
+        const childStore = await this.filterStore(contents, subject.path, false);
+        result.set(childStore, childIdentifiers);
+      }
     }
-    const parent = this.identifierStrategy.getParentContainer(from);
-    return {
-      ...result,
-      ...await this.getAclRecursive(parent, to),
-    };
+    return result;
   }
 
   /**
@@ -279,7 +240,9 @@ export class WebAclReader extends PermissionReader {
     // Find subjects that occur with a given predicate/object, and collect all their triples
     const subjectData = new Store();
     const subjects = store.getSubjects(directAcl ? ACL.terms.accessTo : ACL.terms.default, target, null);
-    subjects.forEach((subject): any => subjectData.addQuads(store.getQuads(subject, null, null, null)));
+    for (const subject of subjects) {
+      subjectData.addQuads(store.getQuads(subject, null, null, null));
+    }
     return subjectData;
   }
 }