Poll-Based Security Event Token (SET) Delivery Using HTTP
RFC 8936



Internet Engineering Task Force (IETF)                   A. Backman, Ed.
Request for Comments: 8936                                        Amazon
Category: Standards Track                                  M. Jones, Ed.
ISSN: 2070-1721                                                Microsoft
                                                            M. Scurtescu
                                                                Coinbase
                                                               M. Ansari
                                                              A. Nadalin
                                                             Independent
                                                           November 2020

       Poll-Based Security Event Token (SET) Delivery Using HTTP

Abstract

   This specification defines how a series of Security Event Tokens
   (SETs) can be delivered to an intended recipient using HTTP POST over
   TLS initiated as a poll by the recipient.  The specification also
   defines how delivery can be assured, subject to the SET Recipient's
   need for assurance.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8936.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and Overview
     1.1.  Notational Conventions
     1.2.  Definitions
   2.  SET Delivery
     2.1.  Polling Delivery using HTTP
     2.2.  Polling HTTP Request
     2.3.  Polling HTTP Response
     2.4.  Poll Request
       2.4.1.  Poll-Only Request
       2.4.2.  Acknowledge-Only Request
       2.4.3.  Poll with Acknowledgement
       2.4.4.  Poll with Acknowledgement and Errors
     2.5.  Poll Response
       2.5.1.  Poll Error Response
     2.6.  Error Response Handling
   3.  Authentication and Authorization
   4.  Security Considerations
     4.1.  Authentication Using Signed SETs
     4.2.  HTTP Considerations
     4.3.  Confidentiality of SETs
     4.4.  Access Token Considerations
       4.4.1.  Bearer Token Considerations
   5.  Privacy Considerations
   6.  IANA Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Appendix A.  Unencrypted Transport Considerations
   Acknowledgments
   Authors' Addresses

1.  Introduction and Overview

   This specification defines how a stream of Security Event Tokens
   (SETs) [RFC8417] can be transmitted to an intended SET Recipient
   using HTTP [RFC7231] over TLS.  The specification defines a method to
   poll for SETs using HTTP POST.  This is an alternative SET delivery
   method to the one defined in [RFC8935].

   Poll-based SET delivery is intended for scenarios where all of the
   following apply:

   *  The recipient of the SET is capable of making outbound HTTP
      requests.

   *  The transmitter is capable of hosting a TLS-enabled HTTP endpoint
      that is accessible to the recipient.

   *  The transmitter and recipient are willing to exchange data with
      one another.

   In some scenarios, either push-based or poll-based delivery could be
   used, and in others, only one of them would be applicable.

   A mechanism for exchanging configuration metadata such as endpoint
   URLs, cryptographic keys, and possible implementation constraints
   such as buffer size limitations between the transmitter and recipient
   is out of scope for this specification.  How SETs are defined and the
   process by which security events are identified for SET Recipients
   are specified in [RFC8417].

1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   Throughout this document, all figures may contain spaces and extra
   line wrapping for readability and due to space limitations.

1.2.  Definitions

   This specification utilizes terminology defined in [RFC8417] and
   [RFC8935].

2.  SET Delivery

   When a SET is available for a SET Recipient, the SET Transmitter
   queues the SET in a buffer so that a SET Recipient can poll for SETs
   using HTTP POST.

   In poll-based SET delivery using HTTP over TLS, zero or more SETs are
   delivered in a JSON [RFC8259] document to a SET Recipient in response
   to an HTTP POST request to the SET Transmitter.  Then in a following
   request, the SET Recipient acknowledges received SETs and can poll
   for more.  All requests and responses are JSON documents and use a
   "Content-Type" of "application/json", as described in Section 2.2.

   After successful (acknowledged) SET delivery, SET Transmitters are
   not required to retain or record SETs for retransmission.  Once a SET
   is acknowledged, the SET Recipient SHALL be responsible for
   retention, if needed.  Transmitters may also discard undelivered SETs
   under deployment-specific conditions, such as if they have not been
   polled for over too long a period of time or if an excessive amount
   of storage is needed to retain them.

   Upon receiving a SET, the SET Recipient reads the SET and validates
   it in the manner described in Section 2 of [RFC8935].  The SET
   Recipient MUST acknowledge receipt to the SET Transmitter, and SHOULD
   do so in a timely fashion, as described in Section 2.4.  The SET
   Recipient SHALL NOT use the event acknowledgement mechanism to report
   event errors other than those relating to the parsing and validation
   of the SET.

2.1.  Polling Delivery using HTTP

   This method allows a SET Recipient to use HTTP POST (Section 4.3.3 of
   [RFC7231]) to acknowledge SETs and to check for and receive zero or
   more SETs.  Requests MAY be made at a periodic interval (short
   polling) or requests MAY wait, pending availability of new SETs using
   long polling, per Section 2 of [RFC6202].  Note that short polling
   will result in retrieving zero or more SETs whereas long polling will
   typically result in retrieving one or more SETs unless a timeout
   occurs.

   The delivery of SETs in this method is facilitated by HTTP POST
   requests initiated by the SET Recipient in which:

   *  The SET Recipient makes a request for available SETs using an HTTP
      POST to a pre-arranged endpoint provided by the SET Transmitter,
      or

   *  after validating previously received SETs, the SET Recipient
      initiates another poll request using HTTP POST that includes
      acknowledgement of previous SETs and requests the next batch of
      SETs.

   The purpose of the acknowledgement is to inform the SET Transmitter
   that delivery has succeeded and redelivery is no longer required.
   Before acknowledgement, SET Recipients validate the received SETs and
   retain them in a manner appropriate to the recipient's requirements.
   The level and method of retention of SETs by SET Recipients is out of
   scope of this specification.

2.2.  Polling HTTP Request

   When initiating a poll request, the SET Recipient constructs a JSON
   document that consists of polling request parameters and SET
   acknowledgement parameters in the form of JSON objects.

   When making a request, the HTTP "Content-Type" header field is set to
   "application/json".

   The following JSON object members are used in a polling request:

   Request Processing Parameters
      maxEvents
         An OPTIONAL integer value indicating the maximum number of
         unacknowledged SETs to be returned.  The SET Transmitter SHOULD
         NOT send more SETs than the specified maximum.  If more than
         the maximum number of SETs are available, the SET Transmitter
         determines which to return first; the oldest SETs available MAY
         be returned first, or another selection algorithm MAY be used,
         such as prioritizing SETs in some manner that makes sense for
         the use case.  A value of "0" MAY be used by SET Recipients
         that would like to perform an acknowledge-only request.  This
         enables the Recipient to use separate HTTP requests for
         acknowledgement and reception of SETs.  If this parameter is
         omitted, no limit is placed on the number of SETs to be
         returned.

      returnImmediately
         An OPTIONAL JSON boolean value that indicates the SET
         Transmitter SHOULD return an immediate response even if no
         results are available (short polling).  The default value is
         "false", which indicates the request is to be treated as an
         HTTP long poll, per Section 2 of [RFC6202].  The timeout for
         the request is part of the configuration between the
         participants, which is out of scope of this specification.

   SET Acknowledgment Parameters
      ack
         A JSON array of strings whose values are the "jti" [RFC7519]
         values of successfully received SETs that are being
         acknowledged.  If there are no outstanding SETs to acknowledge,
         this member is omitted or contains an empty array.  Once a SET
         has been acknowledged, the SET Transmitter is released from any
         obligation to retain the SET.

      setErrs
         A JSON object with one or more members whose keys are the "jti"
         values of invalid SETs received.  The values of these objects
         are themselves JSON objects that describe the errors detected
         using the "err" and "description" values specified in
         Section 2.6.  If there are no outstanding SETs with errors to
         report, this member is omitted or contains an empty JSON
         object.

2.3.  Polling HTTP Response

   In response to a poll request, the SET Transmitter checks for
   available SETs and responds with a JSON document containing the
   following JSON object members:

   sets
      A JSON object containing zero or more SETs being returned.  Each
      member name is the "jti" of a SET to be delivered, and its value
      is a JSON string representing the corresponding SET.  If there are
      no outstanding SETs to be transmitted, the JSON object SHALL be
      empty.  Note that both SETs being transmitted for the first time
      and SETs that are being retransmitted after not having been
      acknowledged are communicated here.

   moreAvailable
      A JSON boolean value that indicates if more unacknowledged SETs
      are available to be returned.  This member MAY be omitted, with
      the meaning being the same as including it with the boolean value
      "false".

   When making a response, the HTTP "Content-Type" header field is set
   to "application/json".

2.4.  Poll Request

   The SET Recipient performs an HTTP POST (see Section 4.3.4 of
   [RFC7231]) to a pre-arranged polling endpoint URI to check for SETs
   that are available.  Because the SET Recipient has no prior SETs to
   acknowledge, the "ack" and "setErrs" request parameters are omitted.

   After a period of time configured in an out-of-band manner between
   the SET Transmitter and Recipient, a SET Transmitter MAY redeliver
   SETs it has previously delivered.  The SET Recipient SHOULD accept
   repeat SETs and acknowledge the SETs regardless of whether the
   Recipient believes it has already acknowledged the SETs previously.
   A SET Transmitter MAY limit the number of times it attempts to
   deliver a SET.

   If the SET Recipient has received SETs from the SET Transmitter, the
   SET Recipient parses and validates that received SETs meet its own
   requirements and SHOULD acknowledge receipt in a timely fashion
   (e.g., seconds or minutes) so that the SET Transmitter can mark the
   SETs as received.  SET Recipients SHOULD acknowledge receipt before
   taking any local actions based on the SETs to avoid unnecessary delay
   in acknowledgement, where possible.

   Poll requests have three variations:
      Poll-Only
         In this scenario, a SET Recipient asks for the next set of
         events where no previous SET deliveries are acknowledged (such
         as in the initial poll request).

      Acknowledge-Only
         In this scenario, a SET Recipient sets the "maxEvents" value to
         "0" along with "ack" and "setErrs" members indicating the SET
         Recipient is acknowledging previously received SETs and does
         not want to receive any new SETs in response to the request.

      Combined Acknowledge and Poll
         In this scenario, a SET Recipient is both acknowledging
         previously received SETs using the "ack" and "setErrs" members
         and will wait for the next group of SETs in the SET
         Transmitters response.

2.4.1.  Poll-Only Request

   In the case where no SETs were received in a previous poll (see
   Figure 7), the SET Recipient simply polls without acknowledgement
   parameters ("ack" and "setErrs").

   The following is a non-normative example request made by a SET
   Recipient that has no outstanding SETs to acknowledge and is polling
   for available SETs at the endpoint "https://notify.idp.example.com/
   Events":

     POST /Events HTTP/1.1
     Host: notify.idp.example.com
     Content-Type: application/json

     {
      "returnImmediately": true
     }

                   Figure 1: Example Initial Poll Request

   A SET Recipient can poll using default parameter values by passing an
   empty JSON object.

   The following is a non-normative example default poll request to the
   endpoint "https://notify.idp.example.com/Events":

     POST /Events HTTP/1.1
     Host: notify.idp.example.com
     Content-Type: application/json

     {}

                   Figure 2: Example Default Poll Request

2.4.2.  Acknowledge-Only Request

   In this variation, the SET Recipient acknowledges previously received
   SETs and indicates it does not want to receive SETs in response by
   setting the "maxEvents" value to "0".  This variation might be used,
   for instance, when a SET Recipient needs to acknowledge received SETs
   independently (e.g., on separate threads) from the process of
   receiving SETs.

   If the poll needs to return immediately, then "returnImmediately"
   MUST also be present with the value "true".  If it is "false", then a
   long poll will still occur until an event is ready to be returned,
   even though no events will be returned.

   The following is a non-normative example poll request with
   acknowledgement of SETs received (for example, as shown in Figure 6):

     POST /Events HTTP/1.1
     Host: notify.idp.example.com
     Content-Type: application/json

     {
       "ack": [
         "4d3559ec67504aaba65d40b0363faad8",
         "3d0c3cf797584bd193bd0fb1bd4e7d30"
       ],
       "maxEvents": 0,
       "returnImmediately": true
     }

                 Figure 3: Example Acknowledge-Only Request

2.4.3.  Poll with Acknowledgement

   This variation allows a recipient thread to simultaneously
   acknowledge previously received SETs and wait for the next group of
   SETs in a single request.

   The following is a non-normative example poll with acknowledgement of
   the SETs received in Figure 6:

     POST /Events HTTP/1.1
     Host: notify.idp.example.com
     Content-Type: application/json

     {
       "ack": [
         "4d3559ec67504aaba65d40b0363faad8",
         "3d0c3cf797584bd193bd0fb1bd4e7d30"
       ],
       "returnImmediately": false
     }

         Figure 4: Example Poll with Acknowledgement and No Errors

   In the above acknowledgement, the SET Recipient has acknowledged
   receipt of two SETs and has indicated it wants to wait until the next
   SET is available.

2.4.4.  Poll with Acknowledgement and Errors

   In the case where errors were detected in previously delivered SETs,
   the SET Recipient MAY use the "setErrs" member to communicate the
   errors in the following poll request.

   The following is a non-normative example of a response acknowledging
   one successfully received SET and one SET with an error from the two
   SETs received in Figure 6:

     POST /Events HTTP/1.1
     Host: notify.idp.example.com
     Content-Language: en-US
     Content-Type: application/json

     {
       "ack": ["3d0c3cf797584bd193bd0fb1bd4e7d30"],
       "setErrs": {
         "4d3559ec67504aaba65d40b0363faad8": {
           "err": "authentication_failed",
           "description": "The SET could not be authenticated"
         }
       },
       "returnImmediately": true
     }

             Figure 5: Example Poll Acknowledgement with Error

2.5.  Poll Response

   In response to a valid poll request, the service provider MAY respond
   immediately if SETs are available to be delivered.  If no SETs are
   available at the time of the request, the SET Transmitter SHALL delay
   responding until a SET is available or the timeout interval has
   elapsed unless the poll request parameter "returnImmediately" is
   present with the value "true".

   As described in Section 2.3, a JSON document is returned containing
   members including "sets", which SHALL contain zero or more SETs.

   The following is a non-normative example response to the request
   shown in Section 2.4.  This example shows two SETs being returned:

   HTTP/1.1 200 OK
   Content-Type: application/json

   {
    "sets":
     {
      "4d3559ec67504aaba65d40b0363faad8":
      "eyJhbGciOiJub25lIn0.
       eyJqdGkiOiI0ZDM1NTllYzY3NTA0YWFiYTY1ZDQwYjAzNjNmYWFkOCIsImlhdC
       I6MTQ1ODQ5NjQwNCwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwi
       YXVkIjpbImh0dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MW
       ZhNWJiYzg3OTU5M2I3NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0Zl
       ZWRzLzVkNzYwNDUxNmIxZDA4NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybj
       ppZXRmOnBhcmFtczpzY2ltOmV2ZW50OmNyZWF0ZSI6eyJyZWYiOiJodHRwczov
       L3NjaW0uZXhhbXBsZS5jb20vVXNlcnMvNDRmNjE0MmRmOTZiZDZhYjYxZTc1Mj
       FkOSIsImF0dHJpYnV0ZXMiOlsiaWQiLCJuYW1lIiwidXNlck5hbWUiLCJwYXNz
       d29yZCIsImVtYWlscyJdfX19.",
      "3d0c3cf797584bd193bd0fb1bd4e7d30":
      "eyJhbGciOiJub25lIn0.
       eyJqdGkiOiIzZDBjM2NmNzk3NTg0YmQxOTNiZDBmYjFiZDRlN2QzMCIsImlhdC
       I6MTQ1ODQ5NjAyNSwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwi
       YXVkIjpbImh0dHBzOi8vamh1Yi5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MW
       ZhNWJiYzg3OTU5M2I3NzU0IiwiaHR0cHM6Ly9qaHViLmV4YW1wbGUuY29tL0Zl
       ZWRzLzVkNzYwNDUxNmIxZDA4NjQxZDc2NzZlZTciXSwic3ViIjoiaHR0cHM6Ly
       9zY2ltLmV4YW1wbGUuY29tL1VzZXJzLzQ0ZjYxNDJkZjk2YmQ2YWI2MWU3NTIx
       ZDkiLCJldmVudHMiOnsidXJuOmlldGY6cGFyYW1zOnNjaW06ZXZlbnQ6cGFzc3
       dvcmRSZXNldCI6eyJpZCI6IjQ0ZjYxNDJkZjk2YmQ2YWI2MWU3NTIxZDkifSwi
       aHR0cHM6Ly9leGFtcGxlLmNvbS9zY2ltL2V2ZW50L3Bhc3N3b3JkUmVzZXRFeH
       QiOnsicmVzZXRBdHRlbXB0cyI6NX19fQ."
     }
   }

                      Figure 6: Example Poll Response

   In the above example, two SETs whose "jti" values are
   "4d3559ec67504aaba65d40b0363faad8" and
   "3d0c3cf797584bd193bd0fb1bd4e7d30" are delivered.

   The following is a non-normative example response to the request
   shown in Section 2.4.1, which indicates that no new SETs or
   unacknowledged SETs are available:

     HTTP/1.1 200 OK
     Content-Type: application/json

     {
      "sets": {}
     }

                  Figure 7: Example No SETs Poll Response

   Upon receiving the JSON document (e.g., as shown in Figure 6), the
   SET Recipient parses and verifies the received SETs and notifies the
   SET Transmitter of successfully received SETs and SETs with errors
   via the next poll request to the SET Transmitter, as described in
   Sections 2.4.3 and 2.4.4.

2.5.1.  Poll Error Response

   In the event of a general HTTP error condition in the context of
   processing a poll request, the service provider responds with the
   applicable HTTP response status code, as defined in Section 6 of
   [RFC7231].

   Service providers MAY respond to any invalid poll request with an
   HTTP response status code of 400 (Bad Request) even when a more
   specific code might apply, for example, if the service provider
   deemed that a more specific code presented an information disclosure
   risk.  When no more specific code might apply, the service provider
   SHALL respond to an invalid poll request with an HTTP status code of
   400.

   The response body for responses to invalid poll requests is left
   undefined, and its contents SHOULD be ignored.

   The following is a non-normative example of a response to an invalid
   poll request:

     HTTP/1.1 400 Bad Request

                   Figure 8: Example Poll Error Response

2.6.  Error Response Handling

   If a SET is invalid, error codes from the IANA "Security Event Token
   Error Codes" registry established by [RFC8935] are used in error
   responses.  As described in Section 2.3 of [RFC8935], an error
   response is a JSON object providing details about the error that
   includes the following name/value pairs:

   err:  A value from the IANA "Security Event Token Error Codes"
      registry that identifies the error.

   description:  A human-readable string that provides additional
      diagnostic information.

   When included as part of a batch of SETs, the above JSON is included
   as part of the "setErrs" member, as defined in Sections 2.2 and
   2.4.4.

   When the SET Recipient includes one or more error responses in a
   request to the SET Transmitter, it must also include in the request a
   "Content-Language" header field whose value indicates the language of
   the error descriptions included in the request.  The method of
   language selection in the case when the SET Recipient can provide
   error messages in multiple languages is out of scope for this
   specification.

3.  Authentication and Authorization

   The SET delivery method described in this specification is based upon
   HTTP over TLS [RFC2818] and standard HTTP authentication and
   authorization schemes, as per [RFC7235].  The TLS server certificate
   MUST be validated using DNS-ID [RFC6125] and/or DNS-Based
   Authentication of Named Entities (DANE) [RFC6698].  As per
   Section 4.1 of [RFC7235], a SET delivery endpoint SHALL indicate
   supported HTTP authentication schemes via the "WWW-Authenticate"
   header field when using HTTP authentication.

   Authorization for the eligibility to provide actionable SETs can be
   determined by using the identity of the SET Issuer, validating the
   identity of the SET Transmitter, or via other employed authentication
   methods.  Likewise, the SET Transmitter may choose to validate the
   identity of the SET Recipient, perhaps using mutual TLS.  Because
   SETs are not commands, SET Recipients are free to ignore SETs that
   are not of interest after acknowledging their receipt.

4.  Security Considerations

4.1.  Authentication Using Signed SETs

   JWS signed SETs can be used (see [RFC7515] and Section 5 of
   [RFC8417]) to enable the SET Recipient to validate that the SET
   Issuer is authorized to provide actionable SETs.

4.2.  HTTP Considerations

   SET delivery depends on the use of the Hypertext Transfer Protocol
   and is thus subject to the security considerations of HTTP (Section 9
   of [RFC7230]) and its related specifications.

4.3.  Confidentiality of SETs

   SETs may contain sensitive information, including Personally
   Identifiable Information (PII), or be distributed through third
   parties.  In such cases, SET Transmitters and SET Recipients MUST
   protect the confidentiality of the SET contents.  In some use cases,
   using TLS to secure the transmitted SETs will be sufficient.  In
   other use cases, encrypting the SET as described in JSON Web
   Encryption (JWE) [RFC7516] will also be required.  The Event delivery
   endpoint MUST support at least TLS version 1.2 [RFC5246] and SHOULD
   support the newest version of TLS that meets its security
   requirements, which as of the time of this publication is TLS 1.3
   [RFC8446].  The client MUST perform a TLS/SSL server certificate
   check using DNS-ID [RFC6125] and/or DANE [RFC6698].  How a SET
   Recipient determines the expected service identity to match the SET
   Transmitter's server certificate against is out of scope for this
   document.  The implementation security considerations for TLS in
   "Recommendations for Secure Use of Transport Layer Security (TLS) and
   Datagram Transport Layer Security (DTLS)" [RFC7525] MUST be followed.

4.4.  Access Token Considerations

   If HTTP Authentication is performed using OAuth access tokens
   [RFC6749], implementers MUST take into account the threats and
   countermeasures documented in Section 8 of [RFC7521].

4.4.1.  Bearer Token Considerations

   Transmitting bearer tokens [RFC6750] using TLS helps prevent their
   interception.

   Bearer tokens SHOULD have a limited lifetime that can be determined
   directly or indirectly (e.g., by checking with a validation service)
   by the service provider.  By expiring tokens, clients are forced to
   obtain a new token (which usually involves re-authentication) for
   continued authorized access.  For example, in OAuth 2.0, a client MAY
   use an OAuth refresh token to obtain a new bearer token after
   authenticating to an authorization server, per Section 6 of
   [RFC6749].

   Implementations supporting OAuth bearer tokens need to factor in
   security considerations of this authorization method [RFC7521].
   Since security is only as good as the weakest link, implementers also
   need to consider authentication choices coupled with OAuth bearer
   tokens.  The security considerations of the default authentication
   method for OAuth bearer tokens, HTTP Basic, are well documented in
   [RFC7617]; therefore, implementers are encouraged to prefer stronger
   authentication methods.

5.  Privacy Considerations

   SET Transmitters should attempt to deliver SETs that are targeted to
   the specific business and protocol needs of subscribers.

   When sharing personally identifiable information or information that
   is otherwise considered confidential to affected users, SET
   Transmitters and Recipients MUST have the appropriate legal
   agreements and user consent or terms of service in place.
   Furthermore, data that needs confidentiality protection MUST be
   encrypted, at least with TLS and sometimes also using JSON Web
   Encryption (JWE) [RFC7516].

   In some cases, subject identifiers themselves may be considered
   sensitive information, such that their inclusion within a SET may be
   considered a violation of privacy.  SET Issuers and SET Transmitters
   should consider the ramifications of sharing a particular subject
   identifier with a SET Recipient (e.g., whether doing so could enable
   correlation and/or de-anonymization of data) and choose appropriate
   subject identifiers for their use cases.

6.  IANA Considerations

   This document has no IANA actions.

7.  References

7.1.  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>.

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,
              <https://www.rfc-editor.org/info/rfc2818>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <https://www.rfc-editor.org/info/rfc6698>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/info/rfc7231>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <https://www.rfc-editor.org/info/rfc7516>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/info/rfc7519>.

   [RFC7521]  Campbell, B., Mortimore, C., Jones, M., and Y. Goland,
              "Assertion Framework for OAuth 2.0 Client Authentication
              and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521,
              May 2015, <https://www.rfc-editor.org/info/rfc7521>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8417]  Hunt, P., Ed., Jones, M., Denniss, W., and M. Ansari,
              "Security Event Token (SET)", RFC 8417,
              DOI 10.17487/RFC8417, July 2018,
              <https://www.rfc-editor.org/info/rfc8417>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8935]  Backman, A., Ed., Jones, M., Ed., Scurtescu, M., Ansari,
              M., and A. Nadalin, "Push-Based Security Event Token (SET)
              Delivery Using HTTP", RFC 8935, DOI 10.17487/RFC8935,
              November 2020, <https://www.rfc-editor.org/info/rfc8935>.

7.2.  Informative References

   [RFC6202]  Loreto, S., Saint-Andre, P., Salsano, S., and G. Wilkins,
              "Known Issues and Best Practices for the Use of Long
              Polling and Streaming in Bidirectional HTTP", RFC 6202,
              DOI 10.17487/RFC6202, April 2011,
              <https://www.rfc-editor.org/info/rfc6202>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <https://www.rfc-editor.org/info/rfc6749>.

   [RFC6750]  Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
              Framework: Bearer Token Usage", RFC 6750,
              DOI 10.17487/RFC6750, October 2012,
              <https://www.rfc-editor.org/info/rfc6750>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235,
              DOI 10.17487/RFC7235, June 2014,
              <https://www.rfc-editor.org/info/rfc7235>.

   [RFC7617]  Reschke, J., "The 'Basic' HTTP Authentication Scheme",
              RFC 7617, DOI 10.17487/RFC7617, September 2015,
              <https://www.rfc-editor.org/info/rfc7617>.

Appendix A.  Unencrypted Transport Considerations

   Earlier versions of this specification made the use of TLS optional
   and described security and privacy considerations resulting from use
   of unencrypted HTTP as the underlying transport.  When the working
   group decided to mandate usage of HTTP over TLS, it also decided to
   preserve the description of these considerations in a non-normative
   manner.

   The considerations for using unencrypted HTTP with this protocol are
   the same as those described in Appendix A of [RFC8935], and are
   therefore not repeated here.

Acknowledgments

   The editors would like to thank the members of the SCIM Working
   Group, which began discussions of provisioning events starting with
   draft-hunt-scim-notify-00 in 2015.  We would like to thank Phil Hunt
   and the other authors of draft-ietf-secevent-delivery-02, upon which
   this specification is based.  We would like to thank the participants
   in the SecEvents Working Group for their contributions to this
   specification.

   Additionally, we would like to thank the following individuals for
   their reviews of this specification: Roman Danyliw, Martin Duke,
   Benjamin Kaduk, Erik Kline, Murray Kucherawy, Warren Kumari, Barry
   Leiba, Mark Nottingham, Alvaro Retana, Yaron Sheffer, Valery Smyslov,
   Robert Sparks, Éric Vyncke, and Robert Wilton.

Authors' Addresses

   Annabelle Backman (editor)
   Amazon

   Email: richanna@amazon.com

   Michael B. Jones (editor)
   Microsoft

   Email: mbj@microsoft.com
   URI:   https://self-issued.info/

   Marius Scurtescu
   Coinbase

   Email: marius.scurtescu@coinbase.com

   Morteza Ansari
   Independent

   Email: morteza@sharppics.com

   Anthony Nadalin
   Independent

   Email: nadalin@prodigy.net