Poll-Based Security Event Token (SET) Delivery Using HTTP
draft-ietf-secevent-http-poll-05

Network Working Group                                    A. Backman, Ed.
Internet-Draft                                                    Amazon
Intended status: Standards Track                           M. Jones, Ed.
Expires: May 21, 2020                                          Microsoft
                                                            M. Scurtescu
                                                                Coinbase
                                                               M. Ansari
                                                                   Cisco
                                                              A. Nadalin
                                                               Microsoft
                                                       November 18, 2019

       Poll-Based Security Event Token (SET) Delivery Using HTTP
                    draft-ietf-secevent-http-poll-05

Abstract

   This specification defines how a series of Security Event Tokens
   (SETs) may 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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 21, 2020.

Copyright Notice

   Copyright (c) 2019 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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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction and Overview . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  SET Delivery  . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Polling Delivery using HTTP . . . . . . . . . . . . . . .   4
     2.2.  Polling HTTP Request  . . . . . . . . . . . . . . . . . .   4
     2.3.  Polling HTTP Response . . . . . . . . . . . . . . . . . .   5
     2.4.  Poll Request  . . . . . . . . . . . . . . . . . . . . . .   6
       2.4.1.  Poll Only Request . . . . . . . . . . . . . . . . . .   6
       2.4.2.  Acknowledge Only Request  . . . . . . . . . . . . . .   7
       2.4.3.  Poll with Acknowledgement . . . . . . . . . . . . . .   8
       2.4.4.  Poll with Acknowledgement and Errors  . . . . . . . .   9
     2.5.  Poll Response . . . . . . . . . . . . . . . . . . . . . .   9
       2.5.1.  Poll Error Response . . . . . . . . . . . . . . . . .  11
     2.6.  Error Response Handling . . . . . . . . . . . . . . . . .  11
   3.  Authentication and Authorization  . . . . . . . . . . . . . .  12
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
     4.1.  Authentication Using Signed SETs  . . . . . . . . . . . .  12
     4.2.  HTTP Considerations . . . . . . . . . . . . . . . . . . .  13
     4.3.  Confidentiality of SETs . . . . . . . . . . . . . . . . .  13
     4.4.  Access Token Considerations . . . . . . . . . . . . . . .  13
       4.4.1.  Bearer Token Considerations . . . . . . . . . . . . .  13
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  14
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  17
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

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 [I-D.ietf-secevent-http-push].

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   A mechanism for exchanging configuration metadata such as endpoint
   URLs and cryptographic key parameters 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
   [I-D.ietf-secevent-http-push].

2.  SET Delivery

   When a SET is available for a SET Recipient, the SET Transmitter
   attempts to deliver the SET by queueing the SET in a buffer so that a
   SET Recipient can poll for SETs using HTTP/1.1 POST.

   In Poll-Based SET Delivery Using HTTP, 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 2.1.

   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.

   Upon receiving a SET, the SET Recipient reads the SET and validates
   it in the manner described in Section 2 of
   [I-D.ietf-secevent-http-push].  The SET Recipient MUST acknowledge
   receipt to the SET Transmitter.  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.

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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].

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

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

   o  after validating previously received SETs, the SET Recipient
      initiates another poll request using HTTP POST that includes
      acknowledgement of previous SETs and waits for 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 SHOULD ensure that received
   SETs have been validated and retained 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.  The request
   payloads are delivered in a JSON document, as described in
   Section 2.4 and Section 2.5.

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

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

   Request Processing Parameters

      maxEvents
         An OPTIONAL JSON integer value indicating the maximum number of
         unacknowledged SETs that SHOULD be returned.  If more than the
         maximum number of SETs are available, the oldest SETs available
         SHOULD be returned first.  A value of "0" MAY be used by SET
         Recipients that would like to perform an acknowledge only

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         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" values of
         successfully received SETs that are being acknowledged.  If
         there are no outstanding SETs to acknowledge, this member is
         omitted.  When acknowledging a SET, 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
         return, this member is omitted.

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 that contains zero or more nested JSON objects.
      Each nested JSON object's key corresponds to the "jti" of a SET to
      be delivered, and its value is a JSON string containing the value
      of the encoded corresponding SET.  If there are no outstanding
      SETs to be transmitted, the JSON object SHALL be empty.

   moreAvailable
      A JSON boolean value that indicates if more unacknowledged SETs
      are available to be returned.

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   When making a response, the HTTP header "Content-Type" 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 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 SHOULD parse and validate received SETs to 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 which 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 which 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 which 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").

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   The following is an example request made by a SET Recipient that has
   no outstanding SETs to acknowledge and is polling for available SETs
   at the endpoint "https://nofity.exampleidp.com/Events":

   POST /Events HTTP/1.1
   Host: notify.exampleidp.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://nofity.exampleidp.com/Events":

   POST /Events HTTP/1.1
   Host: notify.exampleidp.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.

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   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.exampleidp.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.exampleidp.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.

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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.exampleidp.com
   Content-Language: en-US
   Content-Type: application/json

   {
     "ack": ["3d0c3cf797584bd193bd0fb1bd4e7d30"],
     "setErrs": {
       "4d3559ec67504aaba65d40b0363faad8": {
         "err": "jwtAud",
         "description": "The audience value was invalid."
       }
     },
     "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
   "true".

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

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   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.
     eyJqdGkiOiI0ZDM1NTllYzY3NTA0YWFiYTY1ZDQwYjAzNjNmYWFkOCIsImlhdCI6MTQ
     1ODQ5NjQwNCwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwiYXVkIjpbIm
     h0dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg3OTU5M
     2I3NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYwNDUxNmIx
     ZDA4NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybjppZXRmOnBhcmFtczpzY2ltOmV
     2ZW50OmNyZWF0ZSI6eyJyZWYiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20vVXNlcn
     MvNDRmNjE0MmRmOTZiZDZhYjYxZTc1MjFkOSIsImF0dHJpYnV0ZXMiOlsiaWQiLCJuY
     W1lIiwidXNlck5hbWUiLCJwYXNzd29yZCIsImVtYWlscyJdfX19.",
    "3d0c3cf797584bd193bd0fb1bd4e7d30":
     "eyJhbGciOiJub25lIn0.
     eyJqdGkiOiIzZDBjM2NmNzk3NTg0YmQxOTNiZDBmYjFiZDRlN2QzMCIsImlhdCI6MTQ
     1ODQ5NjAyNSwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwiYXVkIjpbIm
     h0dHBzOi8vamh1Yi5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg3OTU5M
     2I3NzU0IiwiaHR0cHM6Ly9qaHViLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYwNDUxNmIx
     ZDA4NjQxZDc2NzZlZTciXSwic3ViIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL1V
     zZXJzLzQ0ZjYxNDJkZjk2YmQ2YWI2MWU3NTIxZDkiLCJldmVudHMiOnsidXJuOmlldG
     Y6cGFyYW1zOnNjaW06ZXZlbnQ6cGFzc3dvcmRSZXNldCI6eyJpZCI6IjQ0ZjYxNDJkZ
     jk2YmQ2YWI2MWU3NTIxZDkifSwiaHR0cHM6Ly9leGFtcGxlLmNvbS9zY2ltL2V2ZW50
     L3Bhc3N3b3JkUmVzZXRFeHQiOnsicmVzZXRBdHRlbXB0cyI6NX19fQ."
   }
  }

                      Figure 6: Example Poll Response

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

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   The following is a non-normative example response to the request
   shown in Section 2.4, 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
   Section 2.4.3 or Section 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 SHOULD respond with
   an appropriate 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.

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

   HTTP/1.1 400 Bad Request

                        Example Poll Error Response

2.6.  Error Response Handling

   If a SET is invalid, error codes from the IANA "Security Event Token
   Delivery Error Codes" registry established by
   [I-D.ietf-secevent-http-push] are used in error responses.  As

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   described in Section 2.3 of [I-D.ietf-secevent-http-push], 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 Delivery 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 Section 2.3 and
   Section 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 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 and depends on the use of TLS and/or standard HTTP
   authentication and authorization schemes, as per [RFC7235].

   As per Section 4.1 of [RFC7235], a SET delivery endpoint SHALL
   indicate supported HTTP authentication schemes via the "WWW-
   Authenticate" header.

   Authorization for the ability to pick-up or deliver SETs can be
   determined by using the identity of the SET issuer, or via other
   employed authentication methods.  Among other benefits,
   authentication can help prevent denial-of-service attacks.  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

   In scenarios where HTTP authorization or TLS mutual authentication
   are not used or are considered weak, JWS signed SETs SHOULD be used
   (see [RFC7515] and Section 5 of [RFC8417]).  This enables the SET

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   Recipient to validate that the SET issuer is authorized to deliver
   the SET.

4.2.  HTTP Considerations

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

   As stated in Section 2.7.1 of [RFC7230], an HTTP requestor MUST NOT
   generate the "userinfo" (i.e., username and password) component (and
   its "@" delimiter) when an "http" URI reference is generated with a
   message, as they are now disallowed in HTTP.

4.3.  Confidentiality of SETs

   SETs may contain sensitive information that is considered Personally
   Identifiable Information (PII).  In such cases, SET Transmitters and
   SET Recipients MUST protect the confidentiality of the SET contents
   by encrypting the SET as described in JWE [RFC7516], using a
   transport-layer security mechanism such as TLS, or both.  If an Event
   delivery endpoint supports TLS, it MUST support at least TLS version
   1.2 [RFC5246] and SHOULD support the newest version of TLS that meets
   its security requirements.  When using TLS, the client MUST perform a
   TLS/SSL server certificate check, per [RFC6125].  Implementation
   security considerations for TLS can be found in "Recommendations for
   Secure Use of TLS and DTLS" [RFC7525].

4.4.  Access Token Considerations

   When using access tokens, such as those issued by OAuth 2.0
   [RFC6749], implementers MUST take into account threats and
   countermeasures documented in Section 8 of [RFC7521].

4.4.1.  Bearer Token Considerations

   Due to the possibility of interception, Bearer tokens MUST be
   exchanged using TLS.

   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].

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   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.  Designating the specific methods of
   authentication and authorization are out of scope for the delivery of
   SETs, however this information is provided as a resource to
   implementers.

5.  Privacy Considerations

   If a SET needs to be retained for audit purposes, a JWS signature MAY
   be used to provide verification of its authenticity.

   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.

   The propagation of subject identifiers can be perceived as personally
   identifiable information.  Where possible, SET Transmitters and
   Recipients SHOULD devise approaches that prevent propagation, for
   example, the passing of a hash value that requires the subscriber to
   already know the subject.

6.  IANA Considerations

   This specification requires no IANA actions.

7.  References

7.1.  Normative References

   [I-D.ietf-secevent-http-push]
              Backman, A., Jones, M., Scurtescu, M., Ansari, M., and A.
              Nadalin, "Push-Based Security Event Token (SET) Delivery
              Using HTTP", draft-ietf-secevent-http-push-07 (work in
              progress), July 2019.

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   [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>.

   [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>.

   [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>.

   [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>.

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   [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>.

7.2.  Informative References

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [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>.

   [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>.

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   [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.  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.

   The editors would like to thank Phil Hunt and the other the authors
   of draft-ietf-secevent-delivery-02, on which this specification is
   based.

   The editors would like to thank the participants in the SecEvents
   working group for their contributions to this specification.

Appendix B.  Change Log

   [[ to be removed by the RFC Editor before publication as an RFC ]]

   Draft 00 - AB - Based on draft-ietf-secevent-delivery-02 with the
   following additions:

   o  Renamed to "Poll-Based SET Token Delivery Using HTTP"

   o  Removed references to the HTTP Push delivery method.

   Draft 01 - mbj:

   o  Addressed problems identified in my 18-Jul-18 review message
      titled "Issues for both the Push and Poll Specs".

   o  Changes to align terminology with RFC 8417, for instance, by using
      the already defined term SET Recipient rather than SET Receiver.

   o  Applied editorial and minor normative corrections.

   o  Updated Marius' contact information.

   o  Begun eliminating redundancies between this specification and
      "Push-Based Security Event Token (SET) Delivery Using HTTP"
      [I-D.ietf-secevent-http-push], referencing, rather that
      duplicating common normative text.

   Draft 02 - mbj:

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   o  Removed vestigial language remaining from when the push and poll
      delivery methods were defined in a common specification.

   o  Replaced remaining uses of the terms Event Transmitter and Event
      Recipient with the correct terms SET Transmitter and SET
      Recipient.

   o  Removed uses of the unnecessary term "Event Stream".

   o  Removed dependencies between the semantics of "maxEvents" and
      "returnImmediately".

   o  Said that PII in SETs is to be encrypted with TLS, JWE, or both.

   o  Corrected grammar and spelling errors.

   Draft 03 - mbj:

   o  Corrected uses of "attribute" to "member" when describing JSON
      objects.

   o  Further alignment with the push draft.

   Draft 04 - AB + mbj

   o  Referenced SET Transmitter definition in http-push.

   o  Removed incorrect normative text regarding SET construction.

   o  Consolidated general out-of-scope items under Introduction.

   o  Removed unnecessary HTTP headers in examples and added Content-
      Type.

   o  Added Content-Language requirement for error descriptions,
      aligning with http-push.

   o  Stated that bearer tokens SHOULD have a limited lifetime.

   o  Minor editorial fixes.

   Draft 05 - AB + mbj

   o  Added normative text defining how to respond to invalid poll
      requests.

   o  Addressed shepherd comments by Yaron Sheffer.

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Authors' Addresses

   Annabelle Backman (editor)
   Amazon

   Email: richanna@amazon.com

   Michael B. Jones (editor)
   Microsoft

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

   Marius Scurtescu
   Coinbase

   Email: marius.scurtescu@coinbase.com

   Morteza Ansari
   Cisco

   Email: morteza.ansari@cisco.com

   Anthony Nadalin
   Microsoft

   Email: tonynad@microsoft.com

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