CDNI Edge Control Metadata
draft-ietf-cdni-edge-control-metadata-02

Content Delivery Networks Interconnection                     A. Siloniz
Internet-Draft                                                Telefonica
Intended status: Standards Track                            G. Goldstein
Expires: 9 January 2025                               Lumen Technologies
                                                             8 July 2024

                       CDNI Edge Control Metadata
                draft-ietf-cdni-edge-control-metadata-02

Abstract

   This specification defines configuration metadata objects related to
   controlling edge access to resources via content delivery networks
   (CDNs) and Open Caching systems.  Configuring Cross-Origin Resource
   Sharing (CORS) access rules and the dynamic generation of CORS
   headers is a key feature of typical configurations, as are the
   ability to define response body compression rules and client
   connection timeouts.

Status of This Memo

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   This Internet-Draft will expire on 9 January 2025.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  MI.CrossoriginPolicy  . . . . . . . . . . . . . . . . . . . .   2
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  MI.CrossoriginPolicy  . . . . . . . . . . . . . . . . . .   5
       3.2.1.  AccessControlAllowOrigin  . . . . . . . . . . . . . .   7
     3.3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  MI.AllowCompress  . . . . . . . . . . . . . . . . . . . . . .   9
   5.  MI.ClientConnectionControl  . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  CDNI Payload Types  . . . . . . . . . . . . . . . . . . .  11
       7.1.1.  CDNI MI CrossoriginPolicy Payload Type  . . . . . . .  11
       7.1.2.  CDNI MI AllowCompress Payload Type  . . . . . . . . .  12
       7.1.3.  CDNI MI ClientConnectionControl Payload Type  . . . .  12
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  13
   10. Informative References  . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   CDNs typically require a set of configuration metadata to provide
   directives for the processing of responses downstream (at the edge
   and in the user agent).  This document specifies GenericMetadata
   objects to meet those requirements, defining edge processing rules
   such as Cross-Origin Resource Sharing (CORS) handling, response
   compression, and client connection failures.

2.  Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  MI.CrossoriginPolicy

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3.1.  Overview

   When a Content Provider's application requests a content that is
   being distributed by a CDN it makes an initial request to a CP's URL
   using a FQDN in the realm of the Content Provider usually.  Depending
   on the CDN architecture used, the response can be a HTTP redirection
   to a different FQDN, typically one that belongs to the CDN realm.
   This situation is known as a shared cross-origin response, but many
   User Agents apply same-origin restrictions to these network requests.

   Cross-origin resource sharing (CORS) is a protocol that allows a HTTP
   client application to access restricted resources from a server on a
   domain different than the domain that served the original request.
   It is defined by the Web Hypertext Application Technology Working
   Group (WHATWG) Fetch Living Standard [WHATWG-FETCH]

   CORS is based on HTTP request and response headers, that must be
   managed appropriately.

   For clarification, it is important to note that the concept of an
   Origin in the CDN context is different from that in the CORS context.
   The former indicates the source from where the CDN acquires content,
   while the latter is related to the source from where the User Agent
   downloaded the instructions to request the content, also known as the
   Referer.

   To permit shared cross-origin network requests, CORS protocol defines
   a set of request and response headers that MUST be present to permit
   access to these restricted resources.  When one or more CDNs are
   involved to process these requests two situations can occur:

   *  CDNs forward the UA request headers to the Content provider
      servers and they forward the response headers generated to the UA

   *  CDNs can include the logic to dynamically generate the required
      response headers based on the UA request without contacting the
      Content provider servers

   The dynamic generation of CORS headers is typical in modern HTTP
   request processing and avoids CORS headers being forwarded to the
   uCDN reducing the load between dCDN and uCDN when the content to be
   delivered is already cached in the dCDN.

   Also consider than there are two type of requests involved in the
   CORS protocol as defined in Section 3.2.2 of [WHATWG-FETCH]

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   *  A CORS request is any HTTP request that includes an Origin header.
      The Origin header is a version of the Referer header that does not
      reveal a path as defined in Section 3.1 of [WHATWG-FETCH]

   *  A CORS preflight request is one CORS request to check if CORS
      protocol is understood by the delivery server and it includes the
      valid CORS response headers.  It uses the OPTIONS method along
      with some other specific request headers to indicate which method
      and headers will be used in a future CORS request to the same
      resource.

   The CDN Interconnection (CDNI) metadata model requires extensions to
   permit an uCDN to declare how a dCDN MUST evaluate and dynamically
   generate the necessary CORS response headers, avoiding the forwarding
   of CORS requests and/or preflight requests to the uCDN.

   Required capabilities:

   *  Set a default value for CORS response headers independent of the
      value of the Origin request header.

   *  Match the value of the Origin request header with a list of valid
      values.  If it is successful the dCDN will inject the appropriate
      CORS response headers.

   *  Set a list of custom response headers that are allowed to be
      exposed to the client using CORS response headers.

   *  Dynamically generate CORS response headers to CORS preflight
      requests including custom header validation, expose headers, and
      methods.

   *  Support credentials validation within CORS.

   Depending on the metadata configuration, the logic to apply by the
   dCDN is:

   *  Validation of the Origin request header - Metadata can include a
      list of valid domains to validate the Origin request header.  If
      it does not match, the CORS response headers MUST NOT be included
      in the dCDN response.  UA with same-origin restrictions will
      prevent access to the resource.

   *  WIldcard usage - If the Origin request header is valid, depending
      on the configuration, the value of the CORS response header to
      include in the response will be the same as the Origin request
      header, or a wildcard.

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   *  Possibility to define default values for CORS response headers
      independent of the value of the Origin request header.

   *  If the UA is expected to use CORS preflight requests, uCDN can
      also configure the dCDN to dynamically generate synthetic
      responses to OPTIONS requests

   When an uCDN configures one or more of the expose-headers, allow-
   methods, allow-headers, allow-credentials, max-age properties the
   dCDN MUST generate synthetic responses to any CORS preflight request
   without contacting the uCDN servers.  In this case the dCDN will add
   the corresponding CORS response headers to every non-empty parameter.

   If no one of those parameters are set in the configuration the dCDN
   MUST forward every CORS preflight request (OPTIONS method) to the
   uCDN servers and process its response before responding to the UA.

3.2.  MI.CrossoriginPolicy

   MI.CrossoriginPolicy is a GenericMetadata object that allows
   configuring dynamically generated CORS headers.

   Property: allow-origin

   *  Description: Validation of simple CORS requests.

   *  Type: Object AccessControlAllowOrigin (Section 3.2.1)

   *  Mandatory-to-Specify: Yes

   Property: expose-headers

   *  Description: A list of header names the dCDN will include in the
      Access-Control-Expose-Headers response header to a CORS preflight
      request.

   *  Type: Array of Field Names as defined in Section 5.1 of [RFC9110]

   *  Mandatory-to-Specify: No.  If not specified, the default behavior
      is to not add the header in the response

   Property: allow-methods

   *  Description: A list of request method tokens the dCDN will include
      in the Access-Control-Allow-Methods response header to a CORS
      preflight request.

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   *  Type: Array of method tokens as defined in Section 9.1 of
      [RFC9110]

   *  Mandatory-to-Specify: No.  If not specified, the default behavior
      is to not add the header in the response

   Property: allow-headers

   *  Description: A list of header names the dCDN will include in the
      Access-Control-Allow-Headers response header to a CORS preflight
      request.

   *  Type: Array of Field Names as defined in Section 5.1 of [RFC9110]

   *  Mandatory-to-Specify: No.  If not specified, the default behavior
      is to not add the header in the response

   Property: allow-credentials

   *  Description: The value the dCDN will include in the Access-
      Control-Allow-Credentials response header to a CORS preflight
      request.

   *  Type: Boolean

   *  Mandatory-to-Specify: No.  If not specified, the default behavior
      is to not add the header in the response

   Property: max-age

   *  Description: The value the dCDN will include in the Access-
      Control-Max-Age response header to a CORS preflight request.

   *  Type: Integer

   *  Mandatory-to-Specify: No.  If not specified, the default behavior
      is to not add the header in the response

   Property: no-origin-response-headers

   *  Description: In the case of a request that has no Origin field,
      return this set of headers with the response.

   *  Type: Array of MI.HTTPHeader objects, defined in Processing Stages
      Metadata [SVTA2032].

   *  Mandatory-to-Specify: No.  If not specified, the default behavior
      is to not add any CORS response headers

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   Property: preflight-only

   *  Description: Setting this flag to "true" the dCDN will only
      generate synthetic responses to OPTIONS requests with proper CORS
      response headers

   *  Type: Boolean

   *  Mandatory-to-Specify: No.  The default is "false", so CORS
      response headers logic will be injected for all HTTP methods

3.2.1.  AccessControlAllowOrigin

   The AccessControlAllowOrigin object has the following properties:

   Property: allow-list

   *  Description: List of valid expressions that will be used to match
      the request Origin header.  The Origin header is an HTTP
      extension.  Its value is a version of the Referer header that does
      not reveal a path in some specific requests and used for cross-
      origin requests.  Permitted values for the Origin header are of
      the form schema://host[:port] as defined in Sections 3.1, 3.2.2
      and 3.2.3 of [RFC3986]

   *  Type: Array of Strings.  Each string represents a pattern for
      matching against the Origin header.  The pattern can contain the
      wildcards "*" and "?", where "*" matches any sequence of pchar
      [RFC3986] or "/" characters (including the empty string) and "?"
      matches exactly one pchar character.  The three literals "$", "*",
      and "?"  MUST be escaped as "$$", "$*", and "$?" (where "$" is the
      designated escape character).  All other characters are treated as
      literals

   *  Mandatory-to-Specify: Yes

   Property: wildcard-return

   *  Description: If set to "true", the dCDN will include a wildcard
      (*) in the Access-Control-Allow-Origin response header.  If
      "false", the dCDN MUST reflect the value of the Origin request
      header in the Access-Control-Allow-Origin response header.

   *  Type: Boolean

   *  Mandatory-to-Specify: Yes

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3.3.  Examples

   The examples below demonstrate how to configure response headers
   dynamically for CORS validation.

   The following is an example of a CORS validation configuration that
   does not include CORS preflight requests:

   {
     "generic-metadata-type": "MI.CrossoriginPolicy",
     "generic-metadata-value": {
       "allow-origin": {
         "allow-list": [
           {
             "pattern": "https://sourcepage.example.com"
           }
         ],
         "wildcard-return": true
       }
     }
   }

                                  Figure 1

   The following is an example of configuration to the dCDN to generate
   synthetic responses to CORS requests and CORS preflight requests:

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   {
     "generic-metadata-type": "MI.CrossoriginPolicy",
     "generic-metadata-value": {
       "allow-origin": {
         "allow-list": [
           {
             "pattern": "*://sourcepage.example.com"
           },
           "wildcard-return": false
         },
         "allow-methods": [ "GET", "POST" ],
         "allow-credentials": true,
         "allow-headers": [ "X-PINGOTHER", "Content-Type" ],
         "expose-headers": [ "X-User", "Authorization" ],
         "max-age": 3600,
         "no-origin-response-headers": [
             {
               "name": "Access-Control-Allow-Origin",
               "value": "https://sourcepage.example.com",
             }
           ],
         "preflight-only": false
       }
     }
   }

                                  Figure 2

4.  MI.AllowCompress

   Downstream CDNs often have the ability to compress HTTP response
   bodies in cases where the client has declared that it can accept
   compressed responses (via an Accept-Encoding header), but the source/
   origin has returned an uncompressed response.

   The specific compression algorithm used by the dCDN is negotiated by
   the client's Accept-Encoding header according to Section 12.5.3 of
   [RFC9110] (including "q=" preferences) and the compression
   capabilities available on the dCDN.

   In addition, HeaderTransform allows the uCDN to normalize, or modify,
   the Accept-Encoding header to allow for fine-grain control over the
   selection of the compression algorithm (e.g., gzip, compress,
   deflate, br, etc.).

   MI.AllowCompress is a new GenericMetadata object that allows the dCDN
   to compress content before sending it to the client.

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   Property: allow-compress

   *  Description: If set to "true", the dCDN SHOULD try to compress the
      response to the client based on the Accept-Encoding request
      header.

   *  Type: Boolean.

   *  Mandatory-to-Specify: No.  The default is "false".

   The following is an example of the usage of MI.AllowCompress:

   {
       "generic-metadata-type": "MI.AllowCompress",
       "generic-metadata-value": {
           "allow-compress": true
       }
   }

                                  Figure 3

5.  MI.ClientConnectionControl

   Configuration metadata is required to define how connections against
   a client are maintained by a dCDN.  In some use cases, like video
   streaming or other critical object delivery, UA applications
   connection to the cache server must be in control to have the best
   user experience possible.  This metadata allows a uCDN to accommodate
   device-specific constraints and performance optimization.  A dCDN can
   also benefit from this configuration metadata to meet its security
   and resource consumption requirements.

   MI.ClientConnectionControl is a new GenericMetadata object that
   specifies how a dCDN SHOULD manage its connections to UAs.

   Property: connection-keep-alive-time-ms

   *  Description: Specifies the time, in milliseconds, to keep an idle
      connection open.

   *  Type: Integer

   *  Mandatory-to-Specify: No.  When not specified, a default value
      selected by the dCDN will be used.

   The following example shows how a connection setup and a keep alive
   timeout can be set for client connections to a dCDN:

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     {
       "generic-metadata-type": "MI.ClientConnectionControl",
       "generic-metadata-value": {
         "connection-keep-alive-time-ms": 3
       }
     }

                                  Figure 4

6.  Security Considerations

   The FCI and MI objects defined in the present document are
   transferred via the interfaces defined in CDNI [RFC8006] which
   describes how to secure these interfaces protecting integrity and
   confidentiality while ensuring the authenticity of the dCDN and uCDN.

7.  IANA Considerations

7.1.  CDNI Payload Types

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

              +----------------------------+---------------+
              | Payload Type               | Specification |
              +----------------------------+---------------+
              | MI.CrossoriginPolicy       | RFCthis       |
              +----------------------------+---------------+
              | MI.AllowCompress           | RFCthis       |
              +----------------------------+---------------+
              | MI.ClientConnectionControl | RFCthis       |
              +----------------------------+---------------+

                       Table 1: CDNI Payload Types

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

7.1.1.  CDNI MI CrossoriginPolicy Payload Type

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

   Interface: MI/FCI

   Encoding: See Section 3

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7.1.2.  CDNI MI AllowCompress Payload Type

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

   Interface: MI/FCI

   Encoding: See Section 4

7.1.3.  CDNI MI ClientConnectionControl Payload Type

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

   Interface: MI/FCI

   Encoding: See Section 5

8.  Acknowledgements

   The authors would like to express their gratitude to the members of
   the Streaming Video Technology Alliance [SVTA] Open Caching Working
   Group for their guidance / contribution / reviews ...)

   Particulary the following people contribute in one or other way to
   the content of this draft:

   *  Guillaume Bichot (Broadpeak)

   *  Christoph Neumann (Broadpeak)

   *  Chris Lemmons (Comcast)

   *  Pankaj Chaudhari (Disney Streaming)

   *  Robert Colantuoni (Disney Streaming)

   *  Will Power (Lumen)

   *  Rajeev RK (picoNETS)

   *  Shmuel Asafi (Qwilt)

   *  Yoav Gressel (Qwilt)

   *  Nir Sopher (Qwilt)

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   *  Arnon Warshavsky (Qwilt)

   *  Eric Klein (Sirius XM)

   *  Francisco Cano Hila (Telefonica)

   *  Ben Rosenblum (Vecima)

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC8006]  Niven-Jenkins, B., Murray, R., Caulfield, M., and K. Ma,
              "Content Delivery Network Interconnection (CDNI)
              Metadata", RFC 8006, DOI 10.17487/RFC8006, December 2016,
              <https://www.rfc-editor.org/info/rfc8006>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/info/rfc9110>.

10.  Informative References

   [SVTA]     SVTA, "Streaming Video Technology Alliance Home Page",
              <https://www.svta.org>.

   [SVTA2032] SVTA, "Processing Stages Metadata Specification",
              <https://svta.org/documents/SVTA2032>.

   [WHATWG-FETCH]
              Web Hypertext Application Technology Working Group
              (WHATWG), "Fetch Standard",
              <https://fetch.spec.whatwg.org>.

Authors' Addresses

   Alfonso Siloniz
   Telefonica
   Spain

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   Email: alfonsosiloniz@gmail.com

   Glenn Goldstein
   Lumen Technologies
   United States of America
   Email: glenng1215@gmail.com

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