Internet-Draft CDNI extensions for HTTPS delegation August 2022
Fieau, et al. Expires 2 February 2023 [Page]
CDNI Working Group
Intended Status:
Standards Track
F. Fieau, Ed.
E. Stephan
S. Mishra

CDNI extensions for HTTPS delegation


This document defines a new Footprint and Capabilities metadata objects to support HTTPS delegation between two or more interconnected CDNs. Specifically, this document outlines CDNI Metadata interface objects for delegation method as published in the ACME-STAR document [RFC9115].

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 2 February 2023.

Table of Contents

1. Introduction

Content delivery over HTTPS using one or more CDNs along the path requires credential management. This specifically applies when an entity delegates delivery of encrypted content to another trusted entity.

[RFC9115] defines a mechanism where an upstream entity, that is, holder of an X.509 certificate can give a temporary delegated authority, via issuing a certificate to one or more downstream entities for the purposes of delivering content on its behalf. Furthermore, the upstream entity has the ability to extend the duration of the certificate automatically and iteratively until it allows the last renewal to end and therefore terminate the use of the certificate authority to the downstream entity.

More specifically, [RFC9115] defines a process where the upstream Content Delivery Network (uCDN), the holder of the domain, generates on-demand an X.509 certificate for the downstream CDN (dCDN). The certificate generation process ensures that the certified public key corresponds to a private key controlled by the downstream CDN. [RFC9115] follows [RFC8739] for Short-Term, Automatically Renewed Certificate (STAR) in the Automated Certificate Management Environment (ACME).

This document defines CDNI Metadata to make use of HTTPS delegation between an uCDN and a dCDN based on the mechanism specified in [RFC9115]. Furthermore, it includes a proposal of IANA registry to enable adding of delegation methods.

Section 2 defines terminology used in this document. Section 3 presents delegation metadata for the FCI interface. Section 4 addresses the metadata for handling HTTPS delegation with the Metadata Interface. Section 5 addresses IANA registry for delegation methods. Section 6 covers the security considerations.

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] and CDNI Footprint and capabilities [RFC8008].

3. Advertising delegation metadata for CDNI through FCI

The Footprint and Capabilities interface as defined in [RFC8008], allows a dCDN to send a FCI capability type object to a uCDN.

The FCI.Metadata object shall allow a dCDN to advertise the capabilities regarding the supported delegation methods and their configuration.

The following is an example of the supported delegated methods capability object for a CDN supporting STAR delegation method.

     "capabilities": [
         "capability-type": "FCI.Metadata",
         "capability-value": {
           "delegation-methods": [
                    "... Other supported delegation methods ..."
         "footprints": [
           <Footprint objects>

4. ACME Delegation metadata for CDNI

This section defines the AcmeStarDelegationMethod object which describes metadata related to the use of ACME/STAR API presented in [RFC9115]

This allows bootstrapping ACME delegation method between a uCDN and a delegate dCDN.

As expressed in [RFC9115], when an origin has set a delegation to a specific domain (i.e., dCDN), the dCDN should present to the end-user client a short-term certificate bound to the master certificate.

dCDN                  uCDN             Content Provider           CA
 |              ACME/STAR proxy        ACME/STAR client    ACME/STAR srv
 |                     |                     |                     |
 | 1. GET Metadata incl. Delegation Method object with CSR template|
 +-------------------->|                     |                     |
 | 200 OK + Metadata incl. CSR template [CDNI]                     |
 |<--------------------+                     |                     |
 | 2. Request delegation: video.dcdn.example + dCDN public key     |
 +-------------------->|                     |                     |
 |                     | 3. Request STAR Cert + dCDN public key    |
 |                     +-------------------->| 4. Request STAR cert|
 |                     |                     |    + Pubkey         |
 |                     |                     |-------------------->|
 |                     |                     | 5. STAR certificate |
 |                     | 6. STAR certificate |<--------------------|
 | 7. STAR certificate |<--------------------+                     |
 +<--------------------|                     |                     |
 |                     |                     |                     |
 | 8. Retrieve STAR certificate (credential-location-uri)          |
 |                     |                     |         9. renew +--|
 |                     |                     |            cert  |  |
 | 10. Star certificate                      |                  +->|
 |  ...                |                     |                     |

Figure 1: Example call-flow of STAR delegation in CDNI showing 2 levels
of delegation

Property: acme-delegations

Below shows both HostMatch and its Metadata related to a host, for example, here is a HostMatch object referencing "" and a list of 2 acme-delegation objects.

     "host": "",
     "host-metadata": {
       "type": "MI.HostMetadata",
       "href": "https://metadata.ucdn.example/host1234"

Following the example above, the metadata is modeled
for ACMEStarDelegationMethod as follows:

  "generic-metadata-value": {
    "acme-delegations": [

5. 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   | RFCthis       |

[RFC Editor: Please replace RFCthis with the published RFC number for
   this document.]

5.1. 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

Encoding: see Section 4

6. Security considerations

Delegation metadata proposed here do not alter nor change Security Considerations as outlined in the following RFCs: An Automatic Certificate Management Environment (ACME) Profile for Generating Delegated Certificates [RFC9115]; the CDNI Metadata [RFC8006] and CDNI Footprint and Capabilities [RFC8008].

The delegation objects properties that are critical should be protected by the proper/mandated encryption and authentication.

7. References

7.1. Normative References

Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma, "Content Delivery Network Interconnection (CDNI) Metadata", RFC 8006, DOI 10.17487/RFC8006, , <>.
Seedorf, J., Peterson, J., Previdi, S., van Brandenburg, R., and K. Ma, "Content Delivery Network Interconnection (CDNI) Request Routing: Footprint and Capabilities Semantics", RFC 8008, DOI 10.17487/RFC8008, , <>.
Sheffer, Y., Lopez, D., Gonzalez de Dios, O., Pastor Perales, A., and T. Fossati, "Support for Short-Term, Automatically Renewed (STAR) Certificates in the Automated Certificate Management Environment (ACME)", RFC 8739, DOI 10.17487/RFC8739, , <>.
Sheffer, Y., López, D., Pastor Perales, A., and T. Fossati, "An Automatic Certificate Management Environment (ACME) Profile for Generating Delegated Certificates", RFC 9115, DOI 10.17487/RFC9115, , <>.

7.2. Informative References

Peterson, L., Davie, B., and R. van Brandenburg, Ed., "Framework for Content Distribution Network Interconnection (CDNI)", RFC 7336, DOI 10.17487/RFC7336, , <>.
Leung, K., Ed. and Y. Lee, Ed., "Content Distribution Network Interconnection (CDNI) Requirements", RFC 7337, DOI 10.17487/RFC7337, , <>.

Authors' Addresses

Frederic Fieau (editor)
40-48, avenue de la Republique
92320 Chatillon
Emile Stephan
2, avenue Pierre Marzin
22300 Lannion
Sanjay Mishra
13100 Columbia Pike
Silver Spring, MD 20904
United States of America