CDNI extensions for HTTPS delegation

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.

Terminology This document uses terminology from CDNI framework documents such as: CDNI framework document , CDNI requirements and CDNI interface specifications documents: CDNI Metadata interface and CDNI Control interface / Triggers .

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

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. ] } ] } ]]>

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.

Extension to HostMetadata object This extension reuses HostMetadata object, as defined in , and adds new "Delegation methods" objects as specified in the following sections. The existence of the delegation methods in a HostMetaData Object shall enable the use of one of this methods, chosen by the delegating entity. The delegation method will be activated for the set of Host defined in the HostMatch. See for more details about delegation methods metadata specification. Example: The HostMatch object can reference a host metadata that points at the delegation information. Delegation metadata are added to HostMetadata object. Below shows both HostMatch and HostMetadata objects related to a host, for example, here is a HostMatch object referencing "video.example.com": 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.

Extension to PathMetadata object This extension reuses PathMetadata object, as defined in , 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, and/or further delegation methods, implies 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 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 for more details about delegation methods metadata specification.

AcmeStarDelegationMethod object This section defines the AcmeStarDelegationMethod object which describes metadata related to the use of ACME/STAR API presented in As expressed in , 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. | | | | 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 .
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 section 3. It should be included in JSON/text format.
Type: JSON
Mandatory-to-Specify: Yes

Metadata Simple Data Type Descriptions This section describes the simple data types that are used for properties for objects in this document.

Periodicity A time value expressed in seconds to indicate a periodicity. Type: Integer

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

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

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

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.