joerghoh commented on code in PR #571: URL: https://github.com/apache/jackrabbit-oak/pull/571#discussion_r875574343
########## oak-doc/src/site/markdown/security/authorization/bestpractices.md: ########## @@ -0,0 +1,270 @@ +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +Best Practices for Authorization +-------------------------------------------------------------------------------- + +<!-- MACRO{toc} --> + +## Before you get started +### Threat Model + +Before you start coding, creating content or setting up access control set aside some time to consider what is needed +when it comes to securing your application (and what could go wrong). In other words: write a threat model and +make sure you keep updating it as you continue developing. + +The following references provide a good overview as well as guidance on how to build a threat model: + +- https://shostack.org/resources/whitepapers/threat-modeling-what-why-how +- https://owasp.org/www-community/Threat_Modeling +- https://owasp.org/www-community/Threat_Modeling_Process + +### Content Modelling + +As suggested in [Jackrabbbit Wiki](https://jackrabbit.apache.org/archive/wiki/JCR/DavidsModel_115513389.html#DavidsModel-Rule#2:Drivethecontenthierarchy,don'tletithappen) +the content hierarchy in your JCR repository should be designed and access control requirements tend to be a good driver. + +Make sure the content design allows for readable and manageable access control setup later on to secure your data. +If extra complexity is required, it might indicate problems with your content model. Properly securing your content +secured might subsequently become increasingly hard and prone to mistakes. + +### Define Roles and Tasks + +Finally, write down basic characteristics and demands of your application without getting into access control details +or making any assumptions on how your needs will reflected in the repository: + +- what roles are present +- what kind of tasks are those roles designed to perform +- define if you have services accessing the repository and what kind of tasks they need to complete + +Note, that this document should be human readable not go into implementation details: +Instead of writing principal 'content-authors' needs jcr:write on /content, defined that you have an asset 'content', +defined what kind of data it contains and how sensitive the data are (similar to the threat model). +Then identify what roles are going to interact with these data and how they interact: for example you may identify +a role that is just reading data, a second role that is expected to read and write and a third one that is will only +approve new content and publish it). + +## General Best Practices + +### Know how to get what you need + +Familiarize yourself with JCR access control management and Oak authorization design and extensions before starting +to edit the permission setup of your Oak installation. This will help you avoid common pitfalls. If you find yourself +granting your _content-writers_ role full access to just get it work, you probably left your application vulnerable. + +- JCR Specification sections [Access Control Management](https://s.apache.org/jcr-2.0-spec/16_Access_Control_Management.html) +and [Permissions and Capabilities](https://s.apache.org/jcr-2.0-spec/9_Permissions_and_Capabilities.html) +- [Oak Authorization Documentation](../authorization.html) with separate sections for [Access Control Management](../accesscontrol.html) and [Permission Evaluation](../permission.html). +- Exercises for authorization topics below https://github.com/apache/jackrabbit-oak/tree/trunk/oak-exercise/src/test/java/org/apache/jackrabbit/oak/exercise/security/authorization + +### Principle of least privilege + +Keep in mind that not having any permissions granted is equivalent to denying everything (which is in +this case redundant). Start without any access and then keep granting permissions as needed, following the +[principle of least privilege](https://en.wikipedia.org/wiki/Principle_of_least_privilege). +In other words: only grant the minimal set of privileges required to perform a particular task. + +### Verification + +Write tests upfront that verify for each role and task the expected effective permissions (see definition of roles) are +granted. Neither less nor more. + +Ideally, your tests will fail as soon as someone is attempting to make any change to the permission setup. +Granting additional permissions may open up the door for a privilege escalation and revoking permissions will break +your application (if it doesn't you didn't follow the principle of least privilege). + +This may also include tests verify that really no permissions are granted at resources that are outside the scope of a +given role/task + +## Oak Specific Best Practices + +### Avoid deny + +All authorization models present with Apache Jackrabbbit Oak start without any access granted by default i.e. +implicit deny everywhere. It is therefore recommended to only grant access where needed and avoid adding explicit +deny access control entries. In particular in combination with subsequent allows the overall effect will be hard to +understand as soon as multiple principals are contained in a given subject. + +Be wary if you find yourself adding combinations of denies and allows as it might highlight problematic patterns in +your content model that will be hard to secure over time. + +### Avoid redundancy + +Don't specify redundant access control setup just to be on the safe side: + +- If access is granted, avoid repeating the same setup down the hierarchy. +- Avoid setup for principals with administrative access for which permission evaluation is omitted. It might even create a false sense of security. + +### Principal by principle + +Oak authorization is designed to work with `java.security.Principal` which is an abstract representation of any kind of +entity like e.g. individual, a role, a corporation, a login id or even an service. + +While JCR specification does not define how the repository knows about principals, Jackrabbit API defines a +[Principal Management](../principal.html) extension. + +#### Not every principal is a user/group + +Oak allows plugging custom sources of principals which are all reflected through the principal management API. +Therefore, don't assume that every principal is backed by a user or a group. The repository's user management is just +one potential source of principals. + +##### Example : everyone + + # everyone always exists even if there is no such group in the user management + + PrincipalManager principalMgr = ((JackrabbitSession) session).getPrincipalManagere(); + Principal everyone = principalManager.getEveryone() + +#### Membership is no guarantee + +Similarly, make sure you evaluate permissions to verify if a subject has access granted instead of checking if a user +is member of a group. How access control defined for a particular group principal affects its members is an +implementation detail of the authorization setup. + +##### Example : administrative access + +In the default authorization model full administrative access can be configured for arbitrary principals. +So, don't assume that there is a group 'administrators' and that its members have full access. + +#### Stick with group principals + +It is preferable to setup access control for group principals instead of individual user principals and then make sure +your `PrincipalProvider` resolves principal membership according to your needs. + +Further note, that the default authorization model will give precedence to user principals upon evaluation in other words +default access control entries for user principals will overwrite the effect of groups irrespective of the order in the list (see next section). + +### Understand default access control and permission management + +#### Remember inheritance + +When designing your access control setup keep in mind that effective permissions are inherited +down the node hierarchy: allowing `jcr:read` for _content-readers_ role on /content will also grant _content-readers_ +access to all nodes and properties in the subtree (e.g. /content/project1 or /content/project1/jcr:title). + +In addition, effective permissions get inherited through (nested) group principals according to the set of +principals resolved and added to the `javax.security.auth.Subject` upon repository login. + +See [Permission Evaluation in Detail](../permission/evaluation.html) for additional information as well as the +exercises at [L3_PrecedenceRulesTest](https://github.com/apache/jackrabbit-oak/blob/trunk/oak-exercise/src/test/java/org/apache/jackrabbit/oak/exercise/security/authorization/permission/L3_PrecedenceRulesTest.java) + +#### Built-in privileges + +JSR 382 defines a set of built-in privileges and how they apply to repository operations (see https://s.apache.org/jcr-2.0-javadoc/javax/jcr/security/Privilege.html). +The default set has been extended by Oak to cover additional features outside of the scope defined by JCR (like e.g. index +or user management). The complete list can be found in [Privilege Management : The Default Implementation](../privilege/default.html). + +The minimal set of privileges required for each repository operation can be looked up in [Mapping API Calls to Privileges](../privilege/mappingtoprivileges.html) +and [Mapping Privileges to Items](../privilege/mappingtoitems.html). + +##### Privileges affecting the parent node + +Note in particular for add/removing a node `jcr:addChildNodes` and `jcr:removeChildNodes` are required on +the parent node respectively i.e. allowing for modification of the child-node collection. +In addition `jcr:removeNode` needs to be granted on the target node of the removal. + +Thus the following subtle difference apply when evaluation effective permissions vs. privileges (see +also [Permissions vs Privileges](../permission/permissionsandprivileges.html)) and exercises at +[L4_PrivilegesAndPermissionsTest.java](https://github.com/apache/jackrabbit-oak/blob/trunk/oak-exercise/src/test/java/org/apache/jackrabbit/oak/exercise/security/authorization/permission/L4_PrivilegesAndPermissionsTest.java)): + + String parentPath = /content/parent + String toRemove = /content/parent/child + String toAdd = /content/parent/newchild + + Session session = ... + + # Testing Privileges + # ---------------------------------------------------------------------------------------- + + AccessControlManager acMgr = session.getAccessControlManager(); + Privilege jcrAddChildNodes = acMgr.privilegeFromName(Privilege.JCR_ADD_CHILD_NODES) + Privilege jcrRemoveChildNodes = acMgr.privilegeFromName(Privilege.JCR_REMOVE_CHILD_NODES) + Privilege jcrRemoveNode = acMgr.privilegeFromName(JCR_REMOVE_NODE) + + # test if (unspecified) child nodes can be added/removed from the parent + acMgr.hasPrivileges(parentPath, new Privilege[]{jcrAddChildNodes, jcrRemoveChildNodes} + + # test if existing child node can be removed + acMgr.hasPrivileges(toRemove, new Privilege[]{jcrRemoveNode} + + + # Testing Permissions (on the target node NOT on the parent) + # ---------------------------------------------------------------------------------------- + + # test if not-yet existing node could be added at /content/parent/newchild + session.hasPermission(toAdd, Session.ACTION_ADD_NODE) Review Comment: to be honest, I have not looked to much into this example. But maybe it might be best if we could expand this to a complete setup to illustrate the difference much better. Or even better, refer to an existing test. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
