CDNI extensions for HTTPS delegation
draft-ietf-cdni-interfaces-https-delegation-03

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).

Status of This Memo

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This Internet-Draft will expire on September 10, 2020.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Known delegation methods
• 4. Extending the CDNI metadata model
• 4.1. Extension to PathMetadata object
• 4.2. Delegation methods
• 4.2.1. AcmeStarDelegationMethod object
• 4.2.2. SubcertsDelegationMethod object
• 5. Metadata Simple Data Type Descriptions
• 5.1. Periodicity
• 6. IANA considerations
• 6.1. CDNI MI AcmeStarDelegationMethod Payload Type
• 6.2. CDNI MI SubCertsDelegationMethod Payload Type
• 7. Security considerations
• 8. Comments and questions
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Authors' Addresses

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 two 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 entities using CDNI interfaces.

This document considers the following two I-Ds that deals with HTTPS delegation:

- Sub-certificates [I-D.ietf-tls-subcerts] in the TLS Working Group.

- Short-term, Automatically-Renewed (STAR) certificates in Automated Certificate Management Environment(ACME) [I-D.ietf-acme-star]

4. 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.

4.1. Extension to PathMetadata object

This extension reuses PathMetadata object, as defined in [RFC8006], and adds new "Delegation methods" objects as specified in the following sections.

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

Example:

The PathMatch object can reference a path-metadata that points at the delegation information. Delegation metadata are added to PathMetaData object.

Below shows both PathMatch and PathMetaData objects related to a path, for example, here /movies/* located at https://metadata.ucdn.example/video.example.com/movies

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 representing the CSR template (see section 4.2)
	    }}]
}

The existence of the "MI.AcmeStarDelegationMethod" object in a PathMetaData Object shall enable the use of one of the AcmeStarDelegation Methods, chosen by the delegating entity. The delegation method will be activated for the set of Path defined in the PathMatch. See Section 4.2 for more details about delegation methods metadata specification.

4.2. Delegation methods

This section defines the delegation methods objects metadata. Those metadata allows bootstrapping a secured delegation by providing the dCDN with the needed parameters to set it up.

4.2.1. 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]

As expressed in [I-D.ietf-acme-star], 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 Server
 |                     |                     |                     |
 | 1. GET Metadata incl. Delegation Method object with CSR template [CDNI]
 +-------------------->|                     |                     |
 | 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. See Section 5.1.
• Type: Periodicity
• 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 [I-D.ietf-acme-star-delegation] section 3. It should be included in JSON/text format.
• Type: JSON
• Mandatory-to-Specify: Yes

4.2.2. SubcertsDelegationMethod object

This section defines the SubcertsDelegationMethod object which describes metadata related to the use of Subcerts as presented in [I-D.ietf-tls-subcerts]

Client                  dCDN                 uCDN                 Content 
   |                     |                     |                  Provider
   |                     |                     |                     |  
   |                     |                     | Certificate         |  
   |                     |                     |<--------------------| 
   |                     | GET Metadata incl. Subcerts method obj    |          
   |                     +-------------------->|                     |                     
   |                     | 200 OK + Metadata   |                     |                    
   |                     |<--------------------+                     |                    
   |                     | Get Subcert         |                     |          
   |                     +-------------------->|                     |                     
   |                     | Subcert             |                     |                    
   |                     |<--------------------+                     |                    
   | Client Hello + Subcert support            |                     |
   +-------------------->|                     |                     |
   | Server Hello + Subcert                    |                     |
   |<--------------------|                     |                     |
   | Certificate         |                     |                     |
   |<--------------------|                     |                     |
   | TLS ServerKeyExchange                     |                     |
   |<--------------------|                     |                     |
   | TLS ClientKeyExchange                     |                     |
   |<--------------------|                     |                     |
   | TLS Finished        |                     |                     |
   |<--------------------|                     |                     |
   |                     |                     |                     | 
   
   Figure 2: Example call-flow of SubCert delegation in CDNI

As expressed in [I-D.ietf-tls-subcerts], when an origin has set a delegation to a downstream entity such as a downstream CDN (i.e. dCDN), the dCDN should present the Origin or uCDN certificate or "delegated_credential" during the TLS handshake [RFC8446] to the end-user client application, instead of its own certificate.

Property: credentials-delegating-entity

• Description: Endpoint ID (IP) of the delegating Entity (uCDN). Endpoint type defined in RFC8006, Section 4.3.3.
• Type: Endpoint
• Mandatory-to-Specify: Yes

Property: credential-recipient-entity

• Description: Endpoint ID (IP) of the delegated entity (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. See Section 5.1.
• Type: Periodicity
• Mandatory-to-Specify: Yes

5. Metadata Simple Data Type Descriptions

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

5.1. Periodicity

A time value expressed in seconds to indicate a periodicity.

Type: Integer

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       |
| MI.SubCertDelegationMethod | 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/FCI

Encoding: see Section 4.2.1

6.2. 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 4.2.2

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].

8. 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.

9. References

9.1. Normative References

9.2. Informative References

Authors' Addresses