CDNI extensions for HTTPS delegation

Abstract

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

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. Extension to 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": [
                    "AcmeStarDelegationDelegationMethod",
                    "... Other delegation methods ..."
           ]
         }
         "footprints": [
           <Footprint objects>
         ]
       }
     ]
   }

5. Extending the CDNI metadata model

This section defines a CDNI extension to the current Metadata interface model that allows bootstrapping delegation methods between a uCDN and a delegate dCDN.¶

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

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

        {
    "hostmetadata": [
            {
        "generic-metadata-type": "MI.AcmeStarDelegationMethod",
        "generic-metadata-value": {
           "star-proxy": "10.2.2.2",
           "acme-server" : "10.2.3.3",
           "credentials-location-uri": “www.ucdn.com/credentials",
           "periodicity": 36000,
           "CSR-template": Json/Text of the CSR template (see 4.2)
            }}]
        }

PathMatch:
{
  "path-pattern": {
   "pattern": "/movies/*",
   "case-sensitive": true
  },
  "path-metadata": {
   "type": "MI.PathMetadata",
   "href": "https://metadata.ucdn.example/video.example.com/movies"
  }
}

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

{
 PathMetadata:
 {
  "metadata": [
    {
        "generic-metadata-type": "MI.AcmeStarDelegationMethod",
        "generic-metadata-value": {
        "star-proxy": "10.2.2.2",
        "acme-server" : "10.2.3.3",
        "credentials-location-uri": “www.ucdn.com/credentials",
        "periodicity": 36000,
        "CSR-template": Json/Text of the CSR template (see section 4.2)
        }}]
 }
}

7. Metadata Simple Data Type Descriptions

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

8. 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.]

9. Security considerations

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

10. Comments and questions

Should dCDN be visible from the Content Provider or not? This would lead to different solutions to handle delegation towards the CP. In most cases, the dCDNs should never be visible to the CP, in order to reduce the burden of certificates generation for dCDN.¶

11. References