Internet Engineering Task Force (IETF) A. Backman, Ed.

Internet Engineering Task Force (IETF) A. Backman, Ed.
Request for Comments: 8935 Amazon
Category: Standards Track M. Jones, Ed.
ISSN: 2070-1721 Microsoft
M. Scurtescu
Coinbase
M. Ansari
A. Nadalin
Independent
November 2020

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

Abstract

This specification defines how a Security Event Token (SET) can be
delivered to an intended recipient using HTTP POST over TLS. The SET
is transmitted in the body of an HTTP POST request to an endpoint
operated by the recipient, and the recipient indicates successful or
failed transmission via the HTTP response.

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/rfc8935.

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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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. Transmitting a SET
2.2. Success Response
2.3. Failure Response
2.4. Security Event Token Error Codes
3. Authentication and Authorization
4. Delivery Reliability
5. Security Considerations
5.1. Authentication Using Signed SETs
5.2. HTTP Considerations
5.3. Confidentiality of SETs
5.4. Denial of Service
5.5. Authenticating Persisted SETs
6. Privacy Considerations
7. IANA Considerations
7.1. Security Event Token Error Codes
7.1.1. Registration Template
7.1.2. Initial Registry Contents
8. References
8.1. Normative References
8.2. Informative References
Appendix A. Unencrypted Transport Considerations
Acknowledgments
Authors' Addresses

1. Introduction and Overview

This specification defines a mechanism by which a transmitter of a
Security Event Token (SET) [RFC8417] can deliver the SET to an
intended SET Recipient via HTTP POST [RFC7231] over TLS. This is an
alternative SET delivery method to the one defined in [RFC8936].

Push-based SET delivery over HTTP POST is intended for scenarios
where all of the following apply:

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

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

* 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 the following terms defined in [RFC8417]:
"Security Event Token (SET)", "SET Issuer", "SET Recipient", and
"Event Payload", as well as the term defined below:

SET Transmitter: An entity that delivers SETs in its possession to
one or more SET Recipients.

2. SET Delivery

To deliver a SET to a given SET Recipient, the SET Transmitter makes
a SET Transmission Request to the SET Recipient, with the SET itself
contained within the request. The SET Recipient replies to this
request with a response either acknowledging successful transmission
of the SET or indicating that an error occurred while receiving,
parsing, and/or validating the SET.

Upon receipt of a SET, the SET Recipient SHALL validate that all of
the following are true:

* The SET Recipient can parse the SET.

* The SET is authentic (i.e., it was issued by the issuer specified
within the SET, and if signed, was signed by a key belonging to
the issuer).

* The SET Recipient is identified as an intended audience of the
SET.

* The SET Issuer is recognized as an issuer that the SET Recipient
is willing to receive SETs from (e.g., the issuer is listed as
allowed by the SET Recipient).

* The SET Recipient is willing to accept this SET from this SET
Transmitter (e.g., the SET Transmitter is expected to send SETs
with the issuer and subject of the SET in question).

The mechanisms by which the SET Recipient performs this validation
are out of scope for this document. SET parsing, issuer
identification, and audience identification are defined in [RFC8417].
The mechanism for validating the authenticity of a SET is deployment
specific and may vary depending on the authentication mechanisms in
use and whether the SET is signed and/or encrypted (See Section 3).

SET Transmitters MAY transmit SETs issued by another entity. The SET
Recipient may accept or reject (i.e., return an error response such
as "access_denied") a SET at its own discretion.

The SET Recipient persists the SET in a way that is sufficient to
meet the SET Recipient's own reliability requirements. The level and
method of retention of SETs by SET Recipients is out of scope of this
specification. Once the SET has been validated and persisted, the
SET Recipient SHOULD immediately return a response indicating that
the SET was successfully delivered. The SET Recipient SHOULD NOT
perform further processing of the SET beyond the required validation
steps prior to sending this response. Any additional steps SHOULD be
executed asynchronously from delivery to minimize the time the SET
Transmitter is waiting for a response.

The SET Transmitter MAY transmit the same SET to the SET Recipient
multiple times, regardless of the response from the SET Recipient.
The SET Recipient MUST respond as it would if the SET had not been
previously received by the SET Recipient. The SET Recipient MUST NOT
expect or depend on a SET Transmitter to retransmit a SET or
otherwise make a SET available to the SET Recipient once the SET
Recipient acknowledges that it was received successfully.

The SET Transmitter should not retransmit a SET unless the SET
Transmitter suspects that previous transmissions may have failed due
to potentially recoverable errors (such as network outage or
temporary service interruption at either the SET Transmitter or SET
Recipient). In all other cases, the SET Transmitter SHOULD NOT
retransmit a SET. The SET Transmitter SHOULD delay retransmission
for an appropriate amount of time to avoid overwhelming the SET
Recipient (see Section 4).

2.1. Transmitting a SET

To transmit a SET to a SET Recipient, the SET Transmitter makes an
HTTP POST request to a TLS-enabled HTTP endpoint provided by the SET
Recipient. The "Content-Type" header field of this request MUST be
"application/secevent+jwt" as defined in Sections 2.3 and 7.2 of
[RFC8417], and the "Accept" header field MUST be "application/json".
The request body MUST consist of the SET itself, represented as a
JSON Web Token (JWT) [RFC7519].

The SET Transmitter MAY include in the request an "Accept-Language"
header field to indicate to the SET Recipient the preferred
language(s) in which to receive error messages.

The mechanisms by which the SET Transmitter determines the HTTP
endpoint to use when transmitting a SET to a given SET Recipient are
not defined by this specification and are deployment specific.

The following is a non-normative example of a SET Transmission
Request:

POST /Events HTTP/1.1
Host: notify.rp.example.com
Accept: application/json
Accept-Language: en-US, en;q=0.5
Content-Type: application/secevent+jwt

eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJIUzI1NiJ9Cg
.
eyJpc3MiOiJodHRwczovL2lkcC5leGFtcGxlLmNvbS8iLCJqdGkiOiI3NTZFNjk
3MTc1NjUyMDY5NjQ2NTZFNzQ2OTY2Njk2NTcyIiwiaWF0IjoxNTA4MTg0ODQ1LC
JhdWQiOiI2MzZDNjk2NTZFNzQ1RjY5NjQiLCJldmVudHMiOnsiaHR0cHM6Ly9zY
2hlbWFzLm9wZW5pZC5uZXQvc2VjZXZlbnQvcmlzYy9ldmVudC10eXBlL2FjY291
bnQtZGlzYWJsZWQiOnsic3ViamVjdCI6eyJzdWJqZWN0X3R5cGUiOiJpc3Mtc3V
iIiwiaXNzIjoiaHR0cHM6Ly9pZHAuZXhhbXBsZS5jb20vIiwic3ViIjoiNzM3NT
YyNkE2NTYzNzQifSwicmVhc29uIjoiaGlqYWNraW5nIn19fQ
.
Y4rXxMD406P2edv00cr9Wf3_XwNtLjB9n-jTqN1_lLc

Figure 1: Example SET Transmission Request

2.2. Success Response

If the SET is determined to be valid, the SET Recipient SHALL
acknowledge successful transmission by responding with HTTP Response
Status Code 202 (Accepted) (see Section 6.3.3 of [RFC7231]). The
body of the response MUST be empty.

The following is a non-normative example of a successful receipt of a
SET.

HTTP/1.1 202 Accepted

Figure 2: Example Successful Delivery Response

2.3. Failure Response

In the event of a general HTTP error condition, the SET Recipient
responds with the applicable HTTP Status Code, as defined in
Section 6 of [RFC7231].

When the SET Recipient detects an error parsing, validating, or
authenticating a SET transmitted in a SET Transmission Request, the
SET Recipient SHALL respond with an HTTP Response Status Code of 400
(Bad Request). The "Content-Type" header field of this response MUST
be "application/json", and the body MUST be a UTF-8 encoded JSON
[RFC8259] object containing the following name/value pairs:

err: A Security Event Token Error Code (see Section 2.4).

description: A UTF-8 string containing a human-readable description
of the error that may provide additional diagnostic information.
The exact content of this field is implementation specific.

The response MUST include a "Content-Language" header field whose
value indicates the language of the error descriptions included in
the response body. If the SET Recipient can provide error
descriptions in multiple languages, they SHOULD choose the language
to use according to the value of the "Accept-Language" header field
sent by the SET Transmitter in the transmission request, as described
in Section 5.3.5 of [RFC7231]. If the SET Transmitter did not send
an "Accept-Language" header field, or if the SET Recipient does not
support any of the languages included in the header field, the SET
Recipient MUST respond with messages that are understandable by an
English-speaking person, as described in Section 4.5 of [RFC2277].

The following is a non-normative example error response indicating
that the key used to encrypt the SET has been revoked.

HTTP/1.1 400 Bad Request
Content-Language: en-US
Content-Type: application/json

{
"err": "invalid_key",
"description": "Key ID 12345 has been revoked."
}

Figure 3: Example Error Response (invalid_key)

The following is a non-normative example error response indicating
that the access token included in the request is expired.

HTTP/1.1 400 Bad Request
Content-Language: en-US
Content-Type: application/json

{
"err": "authentication_failed",
"description": "Access token has expired."
}

Figure 4: Example Error Response (authentication_failed)

The following is a non-normative example error response indicating
that the SET Receiver is not willing to accept SETs issued by the
specified issuer from this particular SET Transmitter.

HTTP/1.1 400 Bad Request
Content-Language: en-US
Content-Type: application/json

{
"err": "invalid_issuer",
"description": "Not authorized for issuer https://iss.example.com/"
}

Figure 5: Example Error Response (access_denied)

2.4. Security Event Token Error Codes

Security Event Token Error Codes are strings that identify a specific
category of error that may occur when parsing or validating a SET.
Every Security Event Token Error Code MUST have a unique name
registered in the IANA "Security Event Token Error Codes" registry
established by Section 7.1.

The following table presents the initial set of Error Codes that are
registered in the IANA "Security Event Token Error Codes" registry:

+=======================+=====================================+
| Error Code | Description |
+=======================+=====================================+
| invalid_request | The request body cannot be parsed |
| | as a SET, or the Event Payload |
| | within the SET does not conform to |
| | the event's definition. |
+-----------------------+-------------------------------------+
| invalid_key | One or more keys used to encrypt or |
| | sign the SET is invalid or |
| | otherwise unacceptable to the SET |
| | Recipient (expired, revoked, failed |
| | certificate validation, etc.). |
+-----------------------+-------------------------------------+
| invalid_issuer | The SET Issuer is invalid for the |
| | SET Recipient. |
+-----------------------+-------------------------------------+
| invalid_audience | The SET Audience does not |
| | correspond to the SET Recipient. |
+-----------------------+-------------------------------------+
| authentication_failed | The SET Recipient could not |
| | authenticate the SET Transmitter. |
+-----------------------+-------------------------------------+
| access_denied | The SET Transmitter is not |
| | authorized to transmit the SET to |
| | the SET Recipient. |
+-----------------------+-------------------------------------+

Table 1: SET Error Codes

Other Error Codes may also be received, as the set of Error Codes is
extensible via the IANA "Security Event Token Error Codes" registry
established in Section 7.1.

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].

Authorization for the eligibility to provide actionable SETs can be
determined by using the identity of the SET Issuer, the identity of
the SET Transmitter, perhaps using mutual TLS, or via other employed
authentication methods. Because SETs are not commands, SET
Recipients are free to ignore SETs that are not of interest.

4. Delivery Reliability

Delivery reliability requirements may vary depending upon the use
cases. This specification defines the response from the SET
Recipient in such a way as to provide the SET Transmitter with the
information necessary to determine what further action is required,
if any, in order to meet their requirements. SET Transmitters with
high reliability requirements may be tempted to always retry failed
transmissions. However, it should be noted that for many types of
SET delivery errors, a retry is extremely unlikely to be successful.
For example, "invalid_request" indicates a structural error in the
content of the request body that is likely to remain when
retransmitting the same SET. Others such as "access_denied" may be
transient, for example, if the SET Transmitter refreshes expired
credentials prior to retransmission.

The SET Transmitter may be unaware of whether or not a SET has been
delivered to a SET Recipient. For example, a network interruption
could prevent the SET Transmitter from receiving the success
response, or a service outage could prevent the SET Transmitter from
recording the fact that the SET was delivered. It is left to the
implementer to decide how to handle such cases, based on their
requirements. For example, it may be appropriate for the SET
Transmitter to retransmit the SET to the SET Recipient, erring on the
side of guaranteeing delivery, or it may be appropriate to assume
delivery was successful, erring on the side of not spending resources
retransmitting previously delivered SETs. Other options, such as
sending the SET to a "dead letter queue" for manual examination may
also be appropriate.

Implementers SHOULD evaluate the reliability requirements of their
use cases and the impact of various retry mechanisms and
retransmission policies on the performance of their systems to
determine an appropriate strategy for handling various error
conditions.

5. Security Considerations

5.1. 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.

5.2. 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.

5.3. 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. TLS MUST be used to
secure the transmitted SETs. In some use cases, encrypting the SET
as described in 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
Transmitter determines the expected service identity to match the SET
Recipient'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.

5.4. Denial of Service

The SET Recipient may be vulnerable to a denial-of-service attack
where a malicious party makes a high volume of requests containing
invalid SETs, causing the endpoint to expend significant resources on
cryptographic operations that are bound to fail. This may be
mitigated by authenticating SET Transmitters with a mechanism such as
mutual TLS. Rate-limiting problematic transmitters is also a
possible means of mitigation.

5.5. Authenticating Persisted SETs

At the time of receipt, the SET Recipient can rely upon TLS
mechanisms, HTTP authentication methods, and/or other context from
the transmission request to authenticate the SET Transmitter and
validate the authenticity of the SET. However, this context is
typically unavailable to systems to which the SET Recipient forwards
the SET, or to systems that retrieve the SET from storage. If the
SET Recipient requires the ability to validate SET authenticity
outside of the context of the transmission request, then the SET
Recipient SHOULD ensure that such SETs have been signed in accordance
with [RFC7515]. Needed context could also be stored with the SET and
retrieved with it.

6. 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.

7. IANA Considerations

7.1. Security Event Token Error Codes

This document defines Security Event Token Error Codes, for which
IANA has created and now maintains a new registry titled "Security
Event Token Error Codes". Initial values for the "Security Event
Token Error Codes" registry are defined in Table 1 and registered
below. Future assignments are to be made through the Specification
Required registration policy [RFC8126] and shall follow the template
below.

Error Codes are intended to be interpreted by automated systems;
therefore, they SHOULD identify classes of errors to which an
automated system could respond in a meaningfully distinct way (e.g.,
by refreshing authentication credentials and retrying the request).

Error Code names are case sensitive. Names may not match other
registered names in a case-insensitive manner unless the Designated
Experts state that there is a compelling reason to allow an
exception.

Criteria that should be applied by the Designated Experts includes
determining whether the proposed registration duplicates existing
functionality, whether it is likely to be of general applicability or
whether it is useful only for a single application, and whether the
registration description is clear.

It is suggested that multiple Designated Experts be appointed who are
able to represent the perspectives of different applications using
this specification in order to enable broadly informed review of
registration decisions. In cases where a registration decision could
be perceived as creating a conflict of interest for a particular
expert, that expert should defer to the judgment of the other
experts.

7.1.1. Registration Template

Error Code
The name of the Security Event Token Error Code, as described in
Section 2.4. The name MUST be a case-sensitive ASCII string
consisting only of letters, digits, and underscore; these are the
characters whose codes fall within the inclusive ranges 0x30-39,
0x41-5A, 0x5F, and 0x61-7A.

Description
A brief human-readable description of the Security Event Token
Error Code.

Change Controller
For error codes registered by the IETF or its working groups, list
"IETF". For all other error codes, list the name of the party
responsible for the registration. Contact information such as
mailing address, email address, or phone number may also be
provided.

Reference
A reference to the document or documents that define the Security
Event Token Error Code. The definition MUST specify the name and
description of the error code and explain under what circumstances
the error code may be used. URIs that can be used to retrieve
copies of each document at no cost SHOULD be included.

7.1.2. Initial Registry Contents

Error Code: invalid_request
Description: The request body cannot be parsed as a SET or the Event
Payload within the SET does not conform to the event's definition.
Change Controller: IETF
Reference: Section 2.4 of RFC 8935

Error Code: invalid_key
Description: One or more keys used to encrypt or sign the SET is
invalid or otherwise unacceptable to the SET Recipient (expired,
revoked, failed certificate validation, etc.).
Change Controller: IETF
Reference: Section 2.4 of RFC 8935

Error Code: invalid_issuer
Description: The SET Issuer is invalid for the SET Recipient.
Change Controller: IETF
Reference: Section 2.4 of RFC 8935

Error Code: invalid_audience
Description: The SET Audience does not correspond to the SET
Recipient.
Change Controller: IETF
Reference: Section 2.4 of RFC 8935

Error Code: authentication_failed
Description: The SET Recipient could not authenticate the SET
Transmitter.
Change Controller: IETF
Reference: Section 2.4 of RFC 8935

Error Code: access_denied
Description: The SET Transmitter is not authorized to transmit the
SET to the SET Recipient.
Change Controller: IETF
Reference: Section 2.4 of RFC 8935

8. References

8.1. 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>.

[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and
Languages", BCP 18, RFC 2277, DOI 10.17487/RFC2277,
January 1998, <https://www.rfc-editor.org/info/rfc2277>.

[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>.

[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>.

[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>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

[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>.

8.2. Informative References

[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>.

[RFC8936] Backman, A., Ed., Jones, M., Ed., Scurtescu, M., Ansari,
M., and A. Nadalin, "Poll-Based Security Event Token (SET)
Delivery Using HTTP", RFC 8936, DOI 10.17487/RFC8936,
November 2020, <https://www.rfc-editor.org/info/rfc8936>.

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 this non-
normative appendix.

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.
When TLS is not used, this means that the SET MUST be encrypted as
described in JWE [RFC7516].

If SETs were allowed to be transmitted over unencrypted channels,
some privacy-sensitive information about them might leak, even though
the SETs themselves are encrypted. For instance, an attacker may be
able to determine whether or not a SET was accepted and the reason
for its rejection or may be able to derive information from being
able to observe the size of the encrypted SET. (Note that even when
TLS is utilized, some information leakage is still possible; message
padding algorithms to prevent side channels remain an open research
topic.)

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 the specification: Joe Clarke, Roman Danyliw, Vijay
Gurbani, Benjamin Kaduk, Erik Kline, Murray Kucherawy, Barry Leiba,
Yaron Sheffer, Robert Sparks, Valery Smyslov, Éric Vyncke, and Robert
Wilton.

Authors' Addresses

Annabelle Backman (editor)
Amazon

Email: [email protected]

Michael B. Jones (editor)
Microsoft

Email: [email protected]
URI: https://self-issued.info/

Marius Scurtescu
Coinbase

Email: [email protected]

Morteza Ansari
Independent

Email: [email protected]

Anthony Nadalin
Independent

Email: [email protected]