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OAK-9614 : Document best pratices for Oak Access Control Management a…
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| <!-- | ||
| 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 | ||
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| 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. | ||
| --> | ||
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| Best Practices for Authorization | ||
| -------------------------------------------------------------------------------- | ||
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| <!-- MACRO{toc} --> | ||
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| ## Before you get started | ||
| ### Threat Model | ||
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| 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. | ||
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| The following references provide a good overview as well as guidance on how to build a threat model: | ||
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| - 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 | ||
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| ### Content Modelling | ||
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| 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. | ||
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| 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. | ||
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| ### Define Roles and Tasks | ||
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| 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: | ||
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| - 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 | ||
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| 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). | ||
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| ## General Best Practices | ||
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| ### Know how to get what you need | ||
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| 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. | ||
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| - 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 | ||
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| ### Principle of least privilege | ||
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| 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. | ||
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| ### Verification | ||
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| Write tests upfront that verify for each role and task the expected effective permissions (see definition of roles) are | ||
| granted. Neither less nor more. | ||
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| 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). | ||
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| This may also include tests verify that really no permissions are granted at resources that are outside the scope of a | ||
| given role/task | ||
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| ## Oak Specific Best Practices | ||
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| ### Avoid deny | ||
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| 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. | ||
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| 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. | ||
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| ### Avoid redundancy | ||
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| Don't specify redundant access control setup just to be on the safe side: | ||
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| - 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. | ||
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| ### Principal by principle | ||
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| 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. | ||
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| While JCR specification does not define how the repository knows about principals, Jackrabbit API defines a | ||
| [Principal Management](../principal.html) extension. | ||
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| #### Not every principal is a user/group | ||
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| 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. | ||
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| ##### Example : everyone | ||
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| # everyone always exists even if there is no such group in the user management | ||
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| PrincipalManager principalMgr = ((JackrabbitSession) session).getPrincipalManagere(); | ||
| Principal everyone = principalManager.getEveryone() | ||
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| #### Membership is no guarantee | ||
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| 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. | ||
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| ##### Example : administrative access | ||
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| 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. | ||
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| #### Stick with group principals | ||
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| 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. | ||
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| 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). | ||
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| ### Understand default access control and permission management | ||
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| #### Remember inheritance | ||
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| 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). | ||
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| 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. | ||
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| 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) | ||
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| #### Built-in privileges | ||
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| 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). | ||
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| 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). | ||
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| ##### Privileges affecting the parent node | ||
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| 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. | ||
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| 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)): | ||
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| String parentPath = /content/parent | ||
| String toRemove = /content/parent/child | ||
| String toAdd = /content/parent/newchild | ||
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| Session session = ... | ||
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| # Testing Privileges | ||
| # ---------------------------------------------------------------------------------------- | ||
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| 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) | ||
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| # test if (unspecified) child nodes can be added/removed from the parent | ||
| acMgr.hasPrivileges(parentPath, new Privilege[]{jcrAddChildNodes, jcrRemoveChildNodes} | ||
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| # test if existing child node can be removed | ||
| acMgr.hasPrivileges(toRemove, new Privilege[]{jcrRemoveNode} | ||
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| # Testing Permissions (on the target node NOT on the parent) | ||
| # ---------------------------------------------------------------------------------------- | ||
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| # test if not-yet existing node could be added at /content/parent/newchild | ||
| session.hasPermission(toAdd, Session.ACTION_ADD_NODE) | ||
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| # test if the existing child node can be removed | ||
| session.hasPermission(toRemove, Session.ACTION_REMOVE) | ||
| session.hasPermission(toRemove, JackrabbitSession.ACTION_REMOVE_NODE) | ||
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| # test if a non-existing node could be removed (not possible with privilege evaluation) | ||
| session.hasPermission(nonExisting, JackrabbitSession.ACTION_REMOVE_NODE | ||
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| #### Use restrictions to limit effect | ||
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| Apart from picking the minimal set of privileges you can further minimize the risk of privilege escalation by | ||
| narrowing the effect of a given access control setup on certain items in the subtree. This is achieved by creating | ||
| access control entries that come with an additional restriction. | ||
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| See section [Restriction Management](restriction.html) for additional details as well as lessons [L7_RestrictionsTest](https://github.com/apache/jackrabbit-oak/blob/trunk/oak-exercise/src/test/java/org/apache/jackrabbit/oak/exercise/security/authorization/accesscontrol/L7_RestrictionsTest.java) | ||
| and [L8_GlobRestrictionTest](https://github.com/apache/jackrabbit-oak/blob/trunk/oak-exercise/src/test/java/org/apache/jackrabbit/oak/exercise/security/authorization/accesscontrol/L8_GlobRestrictionTest.java) | ||
| in the Oak exercise module. | ||
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| #### Access control setup for system user | ||
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| If your Oak setup supports principal-based authorization (see [Managing Access by Principal](principalbased.html)) it is | ||
| recommended to leverage it for system sessions associated with OSGi service. It helps to keep application owned | ||
| access control setup apart from regular content. | ||
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| See also [Service Authentication](https://sling.apache.org/documentation/the-sling-engine/service-authentication.html) in | ||
| Apache Sling. | ||
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| ### Leverage customizations | ||
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| Oak allows for customization and extensions of all parts of the authorization setup. | ||
| If you find yourself struggling to reflect your needs with the built-in functionality, consider extending and customizing | ||
| the authorization configuration of the repository. | ||
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| #### Leverage custom privileges | ||
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| If you identify application specific operations that cannot be reflected using the built in privileges, Oak allows to | ||
| register custom privileges (see section [Privilege Management](../privilege.html#jackrabbit_api)). | ||
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| Note however, that the built-in permission evaluation will not enforce those | ||
| custom privileges. Instead you have to enforce it in your application or by writing a custom authorization model | ||
| (see section [Combining Multiple Authorization Models](composite.html)) | ||
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| In the example above you might find that publishing content cannot easily be secured using built-in privileges and end | ||
| up registering a custom _myapp:publish_ privilege. | ||
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| #### Leverage custom restrictions | ||
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| Default authorization in Oak allows to limit the effect of invidual JCR access control entries by means of restrictions. | ||
| See section [Restriction Management](restriction.html) for the built-in restrictions and instructions on how to plug | ||
| custom restrictions into the security setup. | ||
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| #### Leverage a custom authorization model | ||
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| If you find that that built-in authorization model is not suited to reflect your needs and setting up access control | ||
| becomes cumbersome and overly complex, consider customizing authorization setup (see section [Combining Multiple Authorization Models](composite.html)). | ||
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| The _oak-exercise_ module defines a couple of [examples](https://github.com/apache/jackrabbit-oak/tree/trunk/oak-exercise/src/main/java/org/apache/jackrabbit/oak/exercise/security/authorization/models) | ||
| to illustrate alternative approaches. The corresponding training material is located in section | ||
| [Advanced Authorization Topics](https://github.com/apache/jackrabbit-oak/tree/trunk/oak-exercise/src/test/java/org/apache/jackrabbit/oak/exercise/security/authorization/advanced) |
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