CDNI interfaces update for HTTPS delegation
draft-fieau-cdni-interfaces-https-delegation-01

Abstract

The delivery of content over HTTPS involving multiple CDNs raises credential management issues. This document recalls the methods under study at the IETF. Then it specifies the updates needed in CDNI Control and Metadata interfaces to setup HTTPS delegation between an uCDN and dCDN.

Status of This Memo

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Known delegation methods
• 4. SecuredDelegation object definition
• 5. Delegation methods
• 5.1. AcmeStarDelegationMethod object
• 5.2. SubcertsDelegationMethod object
• 6. Metadata Simple Data Type Descriptions
• 6.1. Periodicity
• 7. IANA considerations
• 7.1. CDNI MI AcmeStarDelegationMethod Payload Type
• 7.2. CDNI MI SubCertsDelegationMethod Payload Type
• 8. Security considerations
• 9. Discussion
• 10. References
• 10.1. Normative References
• 10.2. Informative References
• Authors' Addresses

1. Introduction

When content is delivered over HTTPS using one or more CDNs along the path, credential management is required. This is specifically required when an entity delegates delivery of encrypted content to another trusted entity. This document presents updates needed in CDNI Control and Metadata interfaces to setup HTTPS delegation between an uCDN and dCDN.

Several delegation methods are currently proposed within several IETF working groups (refer to [I-D.fieau-cdni-https-delegation] for an overview of delegation works ongoing at the IETF). They specify separately the provisioning of their credentials.

This document specifies an update to the CDNI control / Triggers and Metadata interfaces to support these methods. Furthermore, it includes a proposal of registry to enable the adding of new methods in the future.

Section 2 is about terminology used in this document. Section 3 presents delegation methods specified at the IETF. Section 4 introduces a secured delegation object for CDNI. Section 5 addresses the delegation methods objects. Section 6 describes simple data types. Section 7 is about an IANA registry for delegation methods. Section 8 raises the security issues. Section 9 opens the discussion.

2. Terminology

This document uses terminology from CDNI framework documents such as CDNi framework document [RFC7336], CDNI requirements [RFC7337] and CDNI interface specifications documents: CDNI Metadata interface [RFC8006], CDNI Control interface / Triggers [RFC8007] and Logging interface [RFC7937].

3. Known delegation methods

A few methods are currently being proposed at the IETF to handle delegation of HTTPS delivery between entities respecting those constraints (refer to [I-D.fieau-cdni-https-delegation]). Note that many of these methods are still an ongoing work at the IETF within specific WGs.

We however anticipate the need to handle delegation in interconnected CDNs and a need to address within the CDNI WG. Despite the types of delegation methods, we need a common framework in CDNI that would provide new requirements on the CDNI interfaces.

This document considers the following methods supporting HTTPS delegation and may be used between two or more CDNs with applicable interface support following the CDNI framework, such as the CI/Triggers and Metadata Interface:

- Sub-certificates [I-D.rescorla-tls-subcerts] likely to be a TLS WG draft.

- Short-term certificates in ACME using STAR API [I-D.ietf-acme-star]

4. SecuredDelegation object definition

As expressed in [I-D.rescorla-tls-subcerts], when HTTPS origin delivery is requested for a specific domain, the delegate, i.e. a dCDN, presents the Origin, or uCDN certificate or even, "delegated_credential" instead of its own certificate at the TLS handshake to the end.

When HTTPS delegation has been set for a specific domain, the dCDN should present the Origin or uCDN certificate or "delegated_credential" instead of its own certificate when content delivery is requested.

The SecuredDelegation object metadata aims at describing a secured delegation between an uCDN and dCDN by indicating the delegated domain, the start and end of a delegation, and the delegation method used.

property: delegateddomain

• type: HostMatch
• Description: It describes the delegated hostname, restricted to Hostname. HostMatch is defined in RFC8006 section 4.3.3. This value should match the SAN value in certificates.

property: pathpattern

• type: PathPattern
• Description: a PathPattern object contains a PathPattern object with a path to match against a resource's URI path in order to trigger the delegation. It is described in RFC8006, 4.1.4.

property: timewindow

• type: TimeWindow
• Description: Describes delegation start and end times. Timewindow is defined in RFC8006 section 4.2.

Property: delegationmethod

• type: DelegationMethod
• Description: the delegation method(s) used between a uCDN and a dCDN (ex. Subcerts, short term cert, etc.), as defined in the next section.

As an example: a SecuredDelegation object (which contains a TimeWindow object, DelegationMethod and a HostMatch) that only allows the dCDN to deliver content to clients between 09:00 01/01/2000 UTC and 17:00 01/01/2000 UTC:

SecuredDelegation object:
{
        "generic-metadata-type": "MI.SecuredDelegation",
        "generic-metadata-value":
        {
            “timewindow”: {start: 946717200, end: 946746000},
            “delegationMethod”: AcmeStarDelegationMethod, 
            “pathpattern”: {
                "pattern": "/movies/*",
                "case-sensitive": true
            },
            ”delegatedDomain": “www.origin.com”, 
        }
}

Such as object shall be conveyed over the CDNI metadata interface.

5. Delegation methods

This section defines the delegation methods objects metadata used by a securedDelegation. Each method consists of 4 phases:

• Bootstrapping: bootstrapping a secured delegation consists in providing the dCDN with enough parameters to set it up, e.g. ACME servers, Key Servers, etc..
• Credential renewal: In case of certificates based approaches, [I-D.rescorla-tls-subcerts] and [I-D.ietf-acme-star], there is a need in CDNI to periodically provision and update credentials (certificates or private keys) on the dCDNs for a given delegated domain.
• Expiration/Revocation: expiration of delegation can occur for multiple reasons: changes in delegation rights, delegation validity is over. In [I-D.rescorla-tls-subcerts] or [I-D.ietf-acme-star] approaches, the uCDN may implicitly enforce revocation and will prevent any dCDN to renew certificates, or access credentials, when delegation is expired.
• Logging: Regarding logging aspects, we consider to log usages and errors related to a delegated domain. As an example, CDNI logs include: supported delegation method(s), credentials renewal requests, credential revocation notice, mutual agreement for selected credential method to use, credentials download status for a specific domain, as well as errors, related to credentials transfer, or crypto aspects such as bad cypher suite supports, revoked delegations, etc.

5.1. AcmeStarDelegationMethod object

This section defines the AcmeStarDelegationMethod object which describes metadata related to the use of Acme Star API presented in [I-D.ietf-acme-star]

Property: starproxy

• Type: Endpoint
• Description: Used to advertise the STAR Proxy to the dCDN. Endpoint type defined in RFC8006, section 4.3.3

Property: acmeserver

• Type: Endpoint
• Description: used to advertise the ACME server to the dCDN. Endpoint type is defined in RFC8006, section 4.3.3

Property: credentialslocationuri

• Type: Link
• Description: expresses the location of the credentials to be fetched by the dCDN. Link type is as defined in RFC8006, section 4.3.1

Property: periodicity

• Type: Periodicity
• description: expresses the credentials renewal periodicity. See next section on simple meta data type.

As an example, AcmeStarDelegationMethod object could express the Acme-Star-delegation as the following:

AcmeStarDelegationMethod: {
    "generic-metadata-type": "MI.AcmeStarDelegationMethod",
    "generic-metadata-value": {
        “starproxy”: “10.2.2.2”,
        “acmeserver”: “10.2.3.3”,
        "credentialslocationuri": “www.ucdn.com/credentials”,
        "periodicity": 36000  
    }
}

5.2. SubcertsDelegationMethod object

TBD

6. Metadata Simple Data Type Descriptions

This section describes the simple data types that are used for properties for objects in this document.

6.1. Periodicity

A time value expressed in seconds.

Type: Integer

7. IANA considerations

This document requests the registration of the following entries under the "CDNI Payload Types" registry hosted by IANA regarding “CDNI delegation”:

	
+----------------------------+---------------+
| Payload Type               | Specification |
+----------------------------+---------------+
| MI.AcmeStarDelegationMethod| TBD           |
| MI.SubCertDelegationMethod | TBD           |
| ...                        |               |
+----------------------------+---------------+

		

7.1. CDNI MI AcmeStarDelegationMethod Payload Type

Purpose: The purpose of this Payload Type is to distinguish AcmeStarDelegationMethod MI objects (and any associated capability advertisement)

Interface: MI/FCI

Encoding: see Section 5.1

7.2. CDNI MI SubCertsDelegationMethod Payload Type

Purpose: The purpose of this Payload Type is to distinguish SubcertsDelegationMethod MI objects (and any associated capability advertisement)

Interface: MI/FCI

Encoding: see Section 5.2

8. Security considerations

The CI/T interface and Metadata interface need only to specify mechanisms for delegation between uCDN and dCDN without the use of actual transfer of encrypting keys within the interface messages. The uCDN actions must be limited to in specifying its support for methods it prefers for delegation, actual delegation and revocation of any delegation. The dCDN similarly, must indicate delegation methods it supports. Any subsequent communications enabling delegation must be limited to the agreed delegation method. Additionally, the HTTPS delegation framework must comply with security considerations as specified within RFC 8007 [CDNI Control Interfaces].

9. Discussion

More prospective works include:

- Keyless SSL / LURK [I-D.mglt-lurk-tls]: No WG is currently addressing Lurk.

- Out-of-Band encoding redirection [I-D.reschke-http-oob-encoding]

Should they be considered as delegation methods for CDNI?

10. References

10.1. Normative References

10.2. Informative References

Authors' Addresses