Network Working GroupI. Young
Internet-DraftUKf
Intended status: InformationalL. Johansson, Ed.
Expires: February 4, 2013NDN
 S. Cantor
 Internet2
 August 3, 2012


The Entity Category SAML Entity Metadata Attribute Types
draft-macedir-entity-attribute-00.xml

Abstract

This document describes a SAML entity attribute which can be used to assign category membership semantics to an entity, and a second attribute for use in claiming interoperation or support for entities in such categories.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

Status of this Memo

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1.  Introduction and Motivation

This document describes a SAML attribute, referred to here as the "entity category attribute", values of which represent entity types or categories. When used with the SAML V2.0 Metadata Extension for Entity Attributes (Cantor, S., Ed., “SAML V2.0 Metadata Extension for Entity Attributes,” August 2009.) [SAML2MetadataAttr] each such entity category attribute value represents a claim that the entity thus labelled meets the requirements of, and is asserted to be a member of, the indicated category.

These category membership claims MAY be used by a relying party to provision policy for release of attributes from an identity provider, to influence user interface decisions such as those related to identity provider discovery, or for any other purpose. In general, the intended uses of any claim of membership in a given category will depend on the details of the category's definition, and will often be included as part of that definition.

Entity category attribute values are URIs, and this document does not specify a controlled vocabulary. Category URIs may therefore be defined by any appropriate authority without any requirement for central registration. It is anticipated that other specifications may provide management and discovery mechanisms for entity category attribute values.

A second SAML attribute, referred to here as the "entity category support attribute", contains URI values which represent claims by an entity to support and/or interoperate with entities in a given category or categories. These values, defined in conjunction with specific entity category values, provide entities in a category with the means to identify peer entities that wish to interact with them in category-specific fashion.



2.  Entity Category Attribute



2.1.  Syntax

Entity category attribute values MUST be URIs. It is RECOMMENDED that http:-scheme or https:-scheme URLs are used, and further RECOMMENDED that each such value resolves to a human-readable document defining the category.

The entity category attribute MUST be encoded as a SAML 2.0 Attribute element with @NameFormat urn:oasis:names:tc:SAML:2.0:attrname-format:uri and @Name http://macedir.org/entity-category.

A SAML entity is associated with one or more categories by including the Attribute element described here in the entity's metadata through use of the [SAML2MetadataAttr] (Cantor, S., Ed., “SAML V2.0 Metadata Extension for Entity Attributes,” August 2009.) metadata extension, in which the Attribute element is contained within an mdattr:EntityAttributes element directly contained within an md:Extensions element directly contained within the entity's md:EntityDescriptor. The meaning of the entity category attribute is undefined by this specification if it appears anywhere else within a metadata instance, or within any other XML document.



2.2.  Semantics

The presence of the entity category attribute within an entity's entity attributes represents a series of claims (one for each attribute value) that the entity is a member of each named category. The precise semantics of such a claim depend on the definition of the category itself.

The definition of the concept of a category is intentionally not addressed in this document, in order to leave it as general as possible. However, to be useful, category definitions SHOULD include the following as appropriate:

If significant changes are made to a category definition, the new version of the category SHOULD be represented by a different category URI.

Entity category attribute value URIs MUST be treated as opaque strings.



2.3.  Entity Category Example

<md:EntityDescriptor xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata"
      entityID="https://service.example.com/entity">
  <md:Extensions>
    <mdattr:EntityAttributes
        xmlns:mdattr="urn:oasis:names:tc:SAML:metadata:attribute">
      <Attribute xmlns="urn:oasis:names:tc:SAML:2.0:assertion"
          NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"
          Name="http://macedir.org/entity-category">
        <AttributeValue>http://example.org/category/dog</AttributeValue>
        <AttributeValue>urn:oid:1.3.6.1.4.1.21829</AttributeValue>
      </Attribute>
    </mdattr:EntityAttributes>
  </md:Extensions>
  ...
</md:EntityDescriptor>


3.  Entity Category Support Attribute



3.1.  Syntax

Entity category support attribute values MUST be URIs. It is RECOMMENDED that http:-scheme or https:-scheme URLs are used, and further RECOMMENDED that each such value resolves to a human-readable document defining the value's semantics. A given entity category value MAY be associated with multiple support values in order to allow for multiple forms of support, participation, or interoperation with entities in the category.

The entity category support attribute MUST be encoded as a SAML 2.0 Attribute element with @NameFormat urn:oasis:names:tc:SAML:2.0:attrname-format:uri and @Name http://macedir.org/entity-category-support.

A SAML entity claims a form of support for entities in one or more categories by including the Attribute element described here in the entity's metadata through use of the [SAML2MetadataAttr] (Cantor, S., Ed., “SAML V2.0 Metadata Extension for Entity Attributes,” August 2009.) metadata extension, in which the Attribute element is contained within an mdattr:EntityAttributes element directly contained within an md:Extensions element directly contained within the entity's md:EntityDescriptor. The meaning of the entity category support attribute is undefined by this specification if it appears anywhere else within a metadata instance, or within any other XML document.



3.2.  Semantics

The presence of the entity category support attribute within an entity's entity attributes represents a series of claims (one for each attribute value) that the entity supports peer entities in a category in a particular fashion. The precise semantics of such a claim depend on the definition of the category support identifier itself. Category support claims will often be defined to be self-asserted.

The definition of the concept of "support" for a category is intentionally not addressed in this document, in order to leave it as general as possible. It is assumed that entity category definitions MAY define one or more support values signifying particular definitions for "support" by peers as motivated by use cases arising from the definition of the category itself.

A common case is expected to be the definition of a single support value whose URI is identical to that defined for the category itself.

If significant changes are made to a category support definition, the new version SHOULD be represented by a different category support URI.

Entity category support attribute value URIs MUST be treated as opaque strings.



3.3.  Entity Category Support Example

<md:EntityDescriptor xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata"
      entityID="https://idp.example.edu/entity">
  <md:Extensions>
    <mdattr:EntityAttributes
        xmlns:mdattr="urn:oasis:names:tc:SAML:metadata:attribute">
      <Attribute xmlns="urn:oasis:names:tc:SAML:2.0:assertion"
          NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"
          Name="http://macedir.org/entity-category-support">
        <AttributeValue>http://example.org/category/dog/basic</AttributeValue>
        <AttributeValue>http://example.org/category/dog/advanced</AttributeValue>
        <AttributeValue>urn:oid:1.3.6.1.4.1.21829</AttributeValue>
      </Attribute>
    </mdattr:EntityAttributes>
  </md:Extensions>
  ...
</md:EntityDescriptor>


4.  Acknowledgements

This work has been a collaborative effort within the REFEDS and MACE-Dir communities. Special thanks to (in no particular order):



5.  IANA Considerations

This memo includes no request to IANA.



6.  Security Considerations

The presence of the entity category attribute within an entity's entity attributes represents a series of claims (one for each attribute value) that the entity is a member of the named categories. Before accepting and acting on such claims, any relying party needs to establish, at a level of assurance sufficient for the intended use, a chain of trust concluding that the claim is justified.

Some of the elements in such a chain of trust might include:

Although entity category support attribute values will often be defined as self-asserted claims by the containing entity, the provenance of the metadata remains relevant to a relying party's decision to accept a claim of support as legitimate, and the specific definition of a support claim will influence the assurance required to act on it.



7. Normative References

[RFC2119] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).
[SAML2MetadataAttr] Cantor, S., Ed., “SAML V2.0 Metadata Extension for Entity Attributes,” August 2009 (PDF).
[SAML2MetadataDRI] La Joie, C., Ed., “SAML V2.0 Metadata Extensions for Registration and Publication Information Version 1.0,” April 2012 (PDF).


Authors' Addresses

  Ian A. Young
  UK Access Management Federation for Education and Research
Email:  ian@iay.org.uk
  
  Leif Johansson (editor)
  NORDUNet
Email:  leifj@sunet.se
  
  Scott Cantor
  Internet2
Email:  cantor.2@osu.edu