Internet-Draft CDNI extensions for HTTPS delegation October 2021
Fieau, et al. Expires 28 April 2022 [Page]
CDNI Working Group
Intended Status:
Standards Track
F. Fieau, Ed.
E. Stephan
S. Mishra

CDNI extensions for HTTPS delegation


The delivery of content over HTTPS involving multiple CDNs raises credential management issues. This document defines metadata in CDNI Control and Metadata interface to setup HTTPS delegation from an Upstream CDN (uCDN) to a Downstream CDN (dCDN).

Status of This Memo

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This Internet-Draft will expire on 28 April 2022.

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.

Several delegation methods are currently proposed within different IETF working groups. They specify different methods for provisioning HTTPS delivery credentials.

This document extends the CDNI Metadata interface to setup HTTPS delegation between an upstream CDN (uCDN) and downstream CDN (dCDN) using the Standardized delegation methods. Furthermore, it includes a proposal of IANA registry to enable adding of new methods.

Section 2 is about terminology used in this document. Section 3 presents delegation methods specified at the IETF. Section 4 addresses the extension for handling HTTPS delegation in CDNI. Section 5 describes simple data types. Section 6 addresses IANA registry for delegation methods. Section 7 covers the security issues. Section 8 is about comments and questions.

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 Control interface / Triggers [RFC8007].

3. Known delegation methods

There are currently Internet drafts within the TLS and ACME working groups adopted to handle delegation of HTTPS delivery between entities.

This Internet Draft (I-D) proposes standardizing HTTPS delegation between the CDN entities using CDNI interfaces.

This document only considers the Short-term, Automatically-Renewed (STAR) certificates in Automated Certificate Management Environment(ACME) [RFC8739]

This document allows the extension to other delegation methods. Those methods can easily be extended to any further methods in the future.

4. Delegation metadata for CDNI FCI

In order for CDNs to negotiate on which methods are supported, the Footprint and Capabilities interface as defined in RFC8008, allows a uCDN to send a FCI capability type objects, named FCI.SupportedDelegationMethods, to dCDN.

The following example shows an exemple of the supported delegated methods capability object serialization for a CDN that supports STAR delegation method.

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

5. Delegation metadata for CDNI

This section defines Delegation metadata using the current Metadata interface model. This allows bootstrapping delegation methods between a uCDN and a delegate dCDN.

This section presents the use of CDNI Delegation metadata of an HostMatch object, as defined in [RFC8006] as specified in the following sections.

The existence of the delegation methods in metadata in a CDNI Object shall enable the use of one of this methods, chosen by the delegating entity. In the case of an HostMatch object, the delegation method will be activated for the set of Host defined in the HostMatch. See Section 5.2 for more details about delegation methods metadata specification.

The HostMatch object can reference a host metadata that points at the delegation information. Delegation metadata are added to a Metadata object.

Below shows both HostMatch its Metadata related to a host, for example, here is a HostMatch object referencing "":

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

Following the example above, the metadata can be modeled
for ACMEStarDelegationMethod as:

    "metadata": [
        "generic-metadata-type": "MI.AcmeStarDelegationMethod",
        "generic-metadata-value": {
           "star-proxy": "",
           "acme-server" : "",
           "credentials-location-uri": “",
           "periodicity": 36000,
           "CSR-template": Json/Text of the CSR template (see 4.2)

This extension allows to explicitly indicate support for a given method. Therefore, the presence (or lack thereof) of an AcmeStarDelegationMethod, and/or further delegation methods, implies support (or lack thereof) for the given method.

Those metadata can apply to other MI objects such as PathMatch object metadata.

5.2. AcmeStarDelegationMethod object

This section defines the AcmeStarDelegationMethod object which describes metadata related to the use of ACME/STAR API presented in [RFC8739]

As expressed in [RFC8739], 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: star-proxy

  • Description: Used to advertise the STAR Proxy to the dCDN. Endpoint type defined in RFC8006, Section 4.3.3.
  • Type: Endpoint
  • Mandatory-to-Specify: Yes

Property: acme-server

  • Description: used to advertise the ACME server to the dCDN. Endpoint type is defined in RFC8006, Section 4.3.3.
  • Type: Endpoint
  • Mandatory-to-Specify: Yes

Property: credentials-location-uri

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

Property: periodicity

  • Description: expresses the credentials renewal periodicity.
  • Type: Integer
  • Mandatory-to-Specify: Yes

Property: CSR-template

  • Description: The CSR template must be included in the metadata when dealing with AcmeStarDelegation Methods. It shall follow the description in [RFC8739] section 3. It should be included in JSON/text format.
  • Type: JSON
  • Mandatory-to-Specify: Yes

6. 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       |
| FCI.SupportedDelegationMethods| RFCthis       |

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

6.1. 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 5

6.2. CDNI FCI SupportedDelegationMethods Payload Type

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

Interface: FCI

Encoding: see Section 4

7. Security considerations

Extensions proposed here do not alter nor change Security Considerations as outlined in the CDNI Metadata and Footprint and Capabilities RFCs [RFC8006].

However there are still some security questions that should be addressed such as: Are there concerns about using this incorrectly or limitations on how this can safely be used?

8. Privacy considerations

Some privacy questions are still pending: Are there any concerns with sharing the information that is in the metadata? Is the metadata safe to redistribute, or is it something that is only valid between adjacent CDNs?

9. References

9.1. Normative References

Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma, "Content Delivery Network Interconnection (CDNI) Metadata", RFC 8006, DOI 10.17487/RFC8006, , <>.
Murray, R. and B. Niven-Jenkins, "Content Delivery Network Interconnection (CDNI) Control Interface / Triggers", RFC 8007, DOI 10.17487/RFC8007, , <>.
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, , <>.

9.2. 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