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php – How do one use ACL to filter a list of domain-objects according to a certain user's permissions (e.g. EDIT)?

Posted by: admin April 23, 2020 Leave a comment

Questions:

When using the ACL implementation in Symfony2 in a web application, we have come across a use case where the suggested way of using the ACLs (checking a users permissions on a single domain object) becomes unfeasible. Thus, we wonder if there exists some part of the ACL API we can use to solve our problem.

The use case is in a controller that prepares a list of domain objects to be presented in a template, so that the user can choose which of her objects she wants to edit. The user does not have permission to edit all of the objects in the database, so the list must be filtered accordingly.

This could (among other solutions) be done according to two strategies:

1) A query filter that appends a given query with the valid object ids from the present user’s ACL for the object(or objects). I.e:

WHERE <other conditions> AND u.id IN(<list of legal object ids here>)

2) A post-query filter that removes the objects the user does not have the correct permissions for after the complete list has been retrieved from the database. I.e:

$objs   = <query for objects>
$objIds = <getting all the permitted obj ids from the ACL>
for ($obj in $objs) {
    if (in_array($obj.id, $objIds) { $result[] = $obj; } 
}
return $result;

The first strategy is preferable as the database is doing all the filtering work, and both require two database queries. One for the ACLs and one for the actual query, but that is probably unavoidable.

Is there any implementation of one of these strategies (or something achieving the desired results) in Symfony2?

How to&Answers:

Assuming that you have a collection of domain objects that you want to check, you can use the security.acl.provider service’s findAcls() method to batch load in advance of the isGranted() calls.

Conditions:

Database was populated with test entities, with object permissions of MaskBuilder::MASK_OWNER for a random user from my database, and class permissions of MASK_VIEW for role IS_AUTHENTICATED_ANONYMOUSLY; MASK_CREATE for ROLE_USER; and MASK_EDIT and MASK_DELETE for ROLE_ADMIN.

Test Code:

$repo = $this->getDoctrine()->getRepository('Foo\Bundle\Entity\Bar');
$securityContext = $this->get('security.context');
$aclProvider = $this->get('security.acl.provider');

$barCollection = $repo->findAll();

$oids = array();
foreach ($barCollection as $bar) {
    $oid = ObjectIdentity::fromDomainObject($bar);
    $oids[] = $oid;
}

$aclProvider->findAcls($oids); // preload Acls from database

foreach ($barCollection as $bar) {
    if ($securityContext->isGranted('EDIT', $bar)) {
        // permitted
    } else {
        // denied
    }
}

RESULTS:

With the call to $aclProvider->findAcls($oids);, the profiler shows that my request contained 3 database queries (as anonymous user).

Without the call to findAcls(), the same request contained 51 queries.

Note that the findAcls() method loads in batches of 30 (with 2 queries per batch), so your number of queries will go up with larger datasets. This test was done in about 15 minutes at the end of the work day; when I have a chance, I’ll go through and review the relevant methods more thoroughly to see if there are any other helpful uses of the ACL system and report back here.

Answer:

Itinerating over the entities is not feasible if you have a couple of thousandth entities – it will keep getting slower and consuming more memory, forcing you to use doctrine batching capabilities, thus making your code more complex (and innefective because after all you need only the ids to make a query – not the whole acl/entities in memory)

What we did to solve this problem is to replace acl.provider service with our own and in that service add a method to make a direct query to the database:

private function _getEntitiesIdsMatchingRoleMaskSql($className, array $roles, $requiredMask)
{
    $rolesSql = array();
    foreach($roles as $role) {
        $rolesSql[] = 's.identifier = ' . $this->connection->quote($role);
    }
    $rolesSql =  '(' . implode(' OR ', $rolesSql) . ')';

    $sql = <<<SELECTCLAUSE
        SELECT 
            oid.object_identifier
        FROM 
            {$this->options['entry_table_name']} e
        JOIN 
            {$this->options['oid_table_name']} oid ON (
            oid.class_id = e.class_id
        )
        JOIN {$this->options['sid_table_name']} s ON (
            s.id = e.security_identity_id
        )     
        JOIN {$this->options['class_table_nambe']} class ON (
            class.id = e.class_id
        )
        WHERE 
            {$this->connection->getDatabasePlatform()->getIsNotNullExpression('e.object_identity_id')} AND
            (e.mask & %d) AND
            $rolesSql AND
            class.class_type = %s
       GROUP BY
            oid.object_identifier    
SELECTCLAUSE;

    return sprintf(
        $sql,
        $requiredMask,
        $this->connection->quote($role),
        $this->connection->quote($className)
    );

} 

Then calling this method from the actual public method that gets the entities ids:

/**
 * Get the entities Ids for the className that match the given role & mask
 * 
 * @param string $className
 * @param string $roles
 * @param integer $mask 
 * @param bool $asString - Return a comma-delimited string with the ids instead of an array
 * 
 * @return bool|array|string - True if its allowed to all entities, false if its not
 *          allowed, array or string depending on $asString parameter.
 */
public function getAllowedEntitiesIds($className, array $roles, $mask, $asString = true)
{

    // Check for class-level global permission (its a very similar query to the one
    // posted above
    // If there is a class-level grant permission, then do not query object-level
    if ($this->_maskMatchesRoleForClass($className, $roles, $requiredMask)) {
        return true;
    }         

    // Query the database for ACE's matching the mask for the given roles
    $sql = $this->_getEntitiesIdsMatchingRoleMaskSql($className, $roles, $mask);
    $ids = $this->connection->executeQuery($sql)->fetchAll(\PDO::FETCH_COLUMN);

    // No ACEs found
    if (!count($ids)) {
        return false;
    }

    if ($asString) {
        return implode(',', $ids);
    }

    return $ids;
}

This way now we can use the code to add filters to DQL queries:

// Some action in a controller or form handler...

// This service is our own aclProvider version with the methods mentioned above
$aclProvider = $this->get('security.acl.provider');

$ids = $aclProvider->getAllowedEntitiesIds('SomeEntityClass', array('role1'), MaskBuilder::VIEW, true);

if (is_string($ids)) {
   $queryBuilder->andWhere("entity.id IN ($ids)");
}
// No ACL found: deny all
elseif ($ids===false) {
   $queryBuilder->andWhere("entity.id = 0")
}
elseif ($ids===true) {
   // Global-class permission: allow all
}

// Run query...etc

Drawbacks: This methods have to be improved to take into account the complexities of ACL inheritance and strategies, but for simple use cases it works fine. Also a cache has to be implemented to avoid the repetitive double query (one with class-level, another with objetc-level)

Answer:

Coupling Symfony ACL back to application and using it as sorting, is not good approach. You are mixing and coupling 2 or 3 layers of application together.
ACL functionality is to answer “YES/NO” to question “Am I allowed to do this?” If you need some sort of owned/editable articles, you can use some column like CreatedBy or group CreatedBy by criteria from another table. Some usergroups or accounts.

Answer:

Use joins, and in case you’re using Doctrine, get it to generate joins for you, as they are almost always faster. Therefore you should design your ACL schema that doing these fast filters are feasible.