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This article is written like a manual or guide. Please help rewrite this article and remove advice or instruction. (June 2023)
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| Paradigm | Declarative programming |
|---|---|
| Designed by | Pablo Giambiagi, David Brossard |
| Developer | Axiomatics |
| First appeared | July 16, 2012; 12 years ago (2012-07-16)[1] |
| Filename extensions | .alfa |
| Website | alfa.guide |
| Major implementations | |
| Axiomatics, Rock Solid Knowledge | |
| Influenced by | |
| XML, XACML | |
| Influenced | |
| Rego, Cedar | |
The Abbreviated Language for Authorization (ALFA) is a domain-specific language used in the formulation of access-control policies.[2]
XACML, the eXtensible Access Control Markup Language, uses XML as its main encoding language. Writing XACML policies directly in XACML leads to bloated, human-unfriendly text,[3] therefore a new, more lightweight, notation was necessary. Axiomatics researcher, Pablo Giambiagi, therefore designed ALFA, the Axiomatics Language for Authorization.
ALFA maps directly into XACML. ALFA contains the same structural elements as XACML i.e. PolicySet, Policy, and Rule.
In March 2014, Axiomatics announced it was donating ALFA to the OASIS XACML Technical Committee[4] in order to advance its standardization.
ALFA was consequently renamed Abbreviated Language for Authorization and filed for standardization.
The words doctor, view, medical record, Singapore... are all examples of attribute values. Attributes make up the building blocks of policies in ABAC and consequently in ALFA.
Just like XACML, ALFA has three structural elements:
Like in XACML, a PolicySet can contain PolicySet and Policy elements. A Policy can contain Rule elements. A Rule contains a decision (either Permit or Deny). In addition, in ALFA, it's possible to add Rule elements to PolicySet and Policy elements. PolicySet, Policy, and Rule elements can be nested or referenced to.
In order to resolve conflicts between siblings, ALFA (as does XACML) uses combining algorithms. There are several combining algorithms that may be used.
ALFA supports all the data types that are defined in the OASIS XACML Core Specification. Some datatypes e.g. numerical (integer, double) and boolean map directly from ALFA to XACML. Others need to be converted such as date or time attributes. To convert an attribute into the relevant data type, use the "value":datatype notation. See below for examples[5]
String, integer, double, and boolean all map directly from ALFA to XACML. They do not need a conversion
namespace exampleBoolean{
policy article{
target clause userRole == "editor" and actionId == "edit" and itemType=="article"
apply firstApplicable
rule publishedArticles{
target clause published == true
permit
}
}
}
The following attribute datatypes need an explicit conversion:
This policy, converts a String value to anyURI.
attribute userDisallowedResources{
category = subjectCat
id = "userDisallowedResources"
type = string
}
rule allowProfileAccess{
target clause url == "http://<host>:<port>/profile/":anyURI
permit
}
The following ALFA example represents a XACML policy which contains a single rule. The policy and rule both have a target. The rule also has a condition which is used to compare 2 attributes together to implement a relationship check (user ID must be equal to owner). Whenever one needs to check 2 attributes together, they must use a condition.
namespace example{
policy article{
target clause itemType=="article"
apply firstApplicable
rule editArticle{
target clause actionId == "edit" and userRole == "editor"
permit
condition userId == owner
}
}
}
namespace exampleTime{
policy checkTimeAccess {
apply firstApplicable
rule checkNightAccess {
target clause role == "supervisor" and document == "medicalrecord"
condition timeInRange(timeOneAndOnly(currentTime), "22:00:00":time, "06:00:00":time)
permit
}
}
}
ALFA can use policy (set) references. They are in fact used implicitly when doing the following.
namespace com.axiomatics{
namespace example{
/**
* A policy about what managers can do. It is linked to from the
* documents policy set.
*/
policy managers{
target clause role == "manager"
apply firstApplicable
rule allowSameDepartment{
condition user.department == document.department
permit
}
}
}
/**
* The main policy. It references the managers policy
*/
policyset documents{
target clause resourceType == "document"
apply firstApplicable
// The following is a policy reference
example.managers
}
}
Obligations and advice are statements in XACML that can be returned from the PDP to the PEP alongside the decision (Permit, Deny...). Obligations and advice are triggered on either Permit or Deny.
namespace example{
import Attributes.*
advice notify = "example.notify"
policy readDocuments{
target clause actionId=="read" and objectType=="document"
apply firstApplicable
/**
* This rule denies access if the time is not between 9 and 5
*/
rule denyOutsideHours{
target clause currentTime<"09:00:00":time or currentTime>"17:00:00":time
deny
on deny{
advice notify{
acme.obligations.message = "You cannot access this service outside office hours"
}
}
}
/**
* This rule grants managers access
*/
rule allowManagers{
target clause acme.user.role=="manager"
permit
}
/**
* This rule catches anything else that might have fallen to this point
*/
rule failsafeDeny{
deny
on deny{
advice notify{
acme.obligations.message = "Your request did not match the policy. Please try again"
}
}
}
}
}
Start by defining the attributes and obligations:
namespace com.axiomatics.examples{
import Attributes.*
obligation breakTheGlass = "com.axiomatics.examples.breakTheGlass"
obligation auditLog = "com.axiomatics.examples.auditLog"
namespace user{
attribute role{
category = subjectCat
id = "com.axiomatics.examples.user.role"
type = string
}
attribute identifier{
category = subjectCat
id = "com.axiomatics.examples.user.identifier"
type = string
}
}
namespace patient{
attribute assignedDoctor{
category = resourceCat
id = "com.axiomatics.examples.user.assignedDoctor"
type = string
}
}
namespace record{
attribute identifier{
category = resourceCat
id = "com.axiomatics.examples.record.identifier"
type = string
}
}
attribute actionId{
category = actionCat
id = "com.axiomatics.examples.actionId"
type = string
}
attribute objectType{
category = resourceCat
id = "com.axiomatics.examples.objectType"
type = string
}
attribute isEmergency{
category = environmentCat
id = "com.axiomatics.examples.isEmergency"
type = boolean
}
attribute message{
category = environmentCat
id = "com.axiomatics.examples.message"
type = string
}
The policy can now be defined with 3 rules:
/**
* Control access to medical records
*/
policy accessMedicalRecord{
target clause actionId == "view" and objectType == "medical record"
apply firstApplicable
/**
* Doctors can view medical records of patients they are assigned to
*/
rule allowRegularAccess{
target clause user.role == "doctor"
condition patient.assignedDoctor == user.identifier
permit
}
/**
* Doctors can view any medical reason in the case of an emergency
*/
rule allowBreakTheGlassAccess{
target clause isEmergency == true
permit
on permit{
obligation auditLog{
message = "A doctor has gotten access to a medical record by breaking the glass"
user.identifier = user.identifier
record.identifier = record.identifier
currentDateTime = currentDateTime
}
}
}
/**
* Deny other accesses. If access is normally denied, tell doctors how
* they can get access by "breaking the glass".
*/
rule denyAccess{
deny
on deny{
obligation breakTheGlass{
message = "You do not have access to this medical record. To be granted access, set the isEmergency flag to true."
record.identifier = record.identifier
currentDateTime = currentDateTime
}
}
}
}
}
The following is an example of an ABAC policy implemented using ALFA. It uses time as attributes. It uses a XACML condition to compare the currentTime attribute to the value representing 5pm (expressed in 24-hour time). Note the use of :time to convert the String value to the right data type.
rule allowAfter5pm{
permit
condition currentTime > "17:00:00":time
}
HL7 defines a series of medical access control use cases which can be easily defined in ALFA.
/* * Access Control Based on Category of Action * URL: https://web.archive.org/web/20160304081703/http://wiki.hl7.org/index.php?title=Security_and_Privacy_Ontology_Use_Cases#Access_Control_Based_on_Category_of_Action#Access_Control_Based_on_Category_of_Action * Access to progress notes */ policy progressNotes{ target clause objectType=="progress note" apply firstApplicable /* * A primary physician can create a patient's progress note */ rule createNote{ target clause role=="physician" and action=="create" condition primaryPhysician==requestorId permit } /* * A physician can update a patient's progress note he/she wrote themselves */ rule updateNote{ target clause role=="physician" and action=="update" condition author==requestorId permit } /* * Safety rule to explicitly deny access unless one of the matching rules above has been matched */ rule safetyHarness{ deny } }
A free extension for the VS Code editor that supports code completion, syntax highlighting, refactoring, and go-to-definition navigation. It can also compile ALFA into XACML 3.0.[6]
The ALFA Plugin for Eclipse is a tool that converts your Eclipse programming IDE to a dedicated editor of authorization policies using ALFA syntax. ALFA policies can then easily be converted into XACML 3.0 policies and loaded into your XACML policy management tool.[7]
