Security Events Working Group A. Backman, Ed.
Internet-Draft Amazon
Intended status: Standards Track M. Jones, Ed.
Expires: November 10, 2019 Microsoft
M. Scurtescu
M. Ansari
A. Nadalin
May 9, 2019

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


This specification defines how a Security Event Token (SET) may be delivered to an intended recipient using HTTP POST. 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 Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on November 10, 2019.

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Table of Contents

1. Introduction and Overview

This specification defines a mechanism by which a transmitter of a Security Event Token (SET) may deliver the SET to an intended recipient via HTTP POST.

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

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 specifications.

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], as well as the terms defined below:

SET Transmitter

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

An entity that receives SETs through some distribution method.

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 mechanisms by which the SET Recipient performs this validation are out of scope for this document. SET parsing and issuer 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 SHOULD ensure that the SET is persisted in a way that is sufficient to meet the SET Recipient's own reliability requirements, and MUST NOT expect or depend on a SET Transmitter to re-transmit or otherwise make available to the SET Recipient a SET once the SET Recipient acknowledges that it was received successfully.

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 extensive business logic that processes the event expressed by the SET prior to sending this response. Such logic SHOULD be executed asynchronously from delivery, in order to minimize the expense and impact of SET delivery on the SET Transmitter.

The SET Transmitter MAY re-transmit a SET if the responses from previous transmissions timed out or indicated potentially recoverable error (such as server unavailability that may be transient). In all other cases, the SET Transmitter SHOULD NOT re-transmit 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 an HTTP endpoint provided by the SET Recipient. The Content-Type header of this request MUST be "application/secevent+jwt" as defined in Sections 2.2 and 6.2 of [RFC8417], and the Accept header MUST be "application/json". The request body MUST consist of the SET itself, represented as a JWT.

The SET Transmitter MAY include in the request an Accept-Language header 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
Accept: application/json
Accept-Language: en-US, en;q=0.5
Content-Type: application/secevent+jwt


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

Note that the purpose of the acknowledgement response is to let the SET Transmitter know that a SET has been delivered and the information no longer needs to be retained by the SET Transmitter. Before acknowledgement, SET Recipients SHOULD ensure they have validated received SETs and retained them in a manner appropriate to information retention requirements appropriate to the SET event types signaled. The level and method of retention of SETs by SET Recipients is out of scope of this specification.

2.3. Failure Response

In the event of a general HTTP error condition, the SET Recipient SHOULD respond with an appropriate 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 of this response MUST be "application/json", and the body MUST be a UTF-8 encoded JSON object containing the following name/value pairs:

A Security Event Token Error Code (see Section 2.4).
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, 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 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, or if the SET Recipient does not support any of the languages included in the header, 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 an example non-normative 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 an example non-normative 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 is expired."

Figure 4: Example Error Response (authentication_failed)

The following is an example non-normative 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": "access_denied",
  "description": "Not authorized for issuer"

Figure 5: Example Error Response (access_denied)

2.4. Security Event Token Delivery Error Codes

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

SET Delivery Error Codes
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. (e.g., expired, revoked, failed certificate validation, etc.)
authentication_failed The SET Recipient could not authenticate the SET Transmitter from the contents of the request.
access_denied The SET Transmitter is not authorized to transmit the provided SET to the SET Recipient.

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].

Because SET Delivery describes a simple function, authorization for the ability to pick-up or deliver SETs can be derived by considering the identity of the SET Issuer, 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 from implementation to implementation. 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 re-transmitting the same SET. Others such as access_denied may be transient, for example if the SET Transmitter refreshes expired credentials prior to re-transmission.

Implementers SHOULD evaluate their reliability requirements and the impact of various retry mechanisms on the performance of their systems to determine the correct strategy for various error conditions.

5. Security Considerations

5.1. 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 Security Considerations). This enables the SET Recipient to validate that the SET Transmitter is authorized to deliver the SET.

5.2. Confidentiality of SETs

SETs may contain sensitive information that is considered Personally Identifiable Information (e.g., subject claims). In such cases, SET Transmitters and SET Recipients MUST protect the confidentiality of the SET contents by encrypting the SET as described in JWE, 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].

5.3. 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 with low runtime overhead, such as mutual TLS.

5.4. Authenticating Persisted SETs

At the time of receipt, the SET Recipient can rely upon transport layer 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 that the SET Recipient forwards the SET onto, 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].

6. Privacy Considerations

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

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.

In some cases subject identifiers themselves may be considered sensitive information, such that its inclusion within a SET may be considered a violation of privacy. 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 case.

7. IANA Considerations

7.1. Security Event Token Delivery Error Codes

This document defines Security Event Token Delivery Error Codes, for which IANA is asked to create and maintain a new registry titled "Security Event Token Delivery Error Codes". Initial values for the Security Event Token Delivery Error Codes registry are given in Table 1. Future assignments are to be made through the First Come First Served registration policy ([RFC8126]) and shall follow the template presented in Section 7.1.1.

Error Codes are intended to be interpreted by automated systems, and therefore 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).

7.1.1. Registration Template

Error Code

The name of the Security Event Token Delivery 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.

A brief human-readable description of the Security Event Token Delivery Error Code.
Change Controller

For error codes registered by the IETF or its working groups, list "IETF SecEvent Working Group". 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.
Defining Document(s)

A reference to the document or documents that define the Security Event Token Delivery 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 Secevent Working Group
Defining Document(s): Section 2.4 of this document

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. (e.g., expired, revoked, failed certificate validation, etc.)
Change Controller: IETF Secevent Working Group
Defining Document(s): Section 2.4 of this document

Error Code: authentication_failed
Description: The SET Recipient could not authenticate the SET Transmitter from the contents of the request.
Change Controller: IETF Secevent Working Group
Defining Document(s): Section 2.4 of this document

Error Code: access_denied
Description: The SET Transmitter is not authorized to transmit the SET to the SET Recipient.
Change Controller: IETF Secevent Working Group
Defining Document(s): Section 2.4 of this document

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.
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, DOI 10.17487/RFC2277, January 1998.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008.
[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.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014.
[RFC7515] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", RFC 7516, DOI 10.17487/RFC7516, May 2015.
[RFC7519] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015.
[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.
[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.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8259] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017.
[RFC8417] Hunt, P., Jones, M., Denniss, W. and M. Ansari, "Security Event Token (SET)", RFC 8417, DOI 10.17487/RFC8417, July 2018.

8.2. Informative References

[RFC7235] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Authentication", RFC 7235, DOI 10.17487/RFC7235, June 2014.

Appendix A. Other Streaming Specifications

[[EDITORS NOTE: This section to be removed prior to publication]]

The following pub/sub, queuing, streaming systems were reviewed as possible solutions or as input to the current draft:

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

In addition to this specification, the WG is defining a polling-based SET delivery protocol. That protocol's draft (draft-ietf-secevent-http-poll) describes it as:

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.

XMPP Events

The WG considered the XMPP events ands its ability to provide a single messaging solution without the need for both polling and push modes. The feeling was the size and methodology of XMPP was to far apart from the current capabilities of the SECEVENTs community which focuses in on HTTP based service delivery and authorization.

Amazon Simple Notification Service

Simple Notification Service, is a pub/sub messaging product from AWS. SNS supports a variety of subscriber types: HTTP/HTTPS endpoints, AWS Lambda functions, email addresses (as JSON or plain text), phone numbers (via SMS), and AWS SQS standard queues. It doesn’t directly support pull, but subscribers can get the pull model by creating an SQS queue and subscribing it to the topic. Note that this puts the cost of pull support back onto the subscriber, just as it is in the push model. It is not clear that one way is strictly better than the other; larger, sophisticated developers may be happy to own message persistence so they can have their own internal delivery guarantees. The long tail of OIDC clients may not care about that, or may fail to get it right. Regardless, I think we can learn something from the Delivery Policies supported by SNS, as well as the delivery controls that SQS offers (e.g., Visibility Timeout, Dead-Letter Queues). I’m not suggesting that we need all of these things in the spec, but they give an idea of what features people have found useful.

Other information:

Apache Kafka

Apache Kafka is an Apache open source project based upon TCP for distributed streaming. It prescribes some interesting general purpose features that seem to extend far beyond the simpler streaming model SECEVENTs is after. A comment from MS has been that Kafka does an acknowledge with poll combination event which seems to be a performance advantage. See:

Google Pub/Sub

Google Pub Sub system favours a model whereby polling and acknowledgement of events is done as separate endpoints as separate functions.


Appendix B. 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 authors of draft-ietf-secevent-delivery-02, on which this draft is based.

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

Appendix C. Change Log

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

Draft 01 - AB:

Draft 02 - AB:

Draft 03 - mbj:

Draft 04 - AB:

Draft 05 - AB:

Authors' Addresses

Annabelle Backman (editor) Amazon EMail:
Michael B. Jones (editor) Microsoft EMail: URI:
Marius Scurtescu Coinbase EMail:
Morteza Ansari Cisco EMail:
Anthony Nadalin Microsoft EMail: