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 carefully, as they describe your rights and restrictions with respect 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

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].¶

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).¶

  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

  HTTP/1.1 202 Accepted

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

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    "description": "Key ID 12345 has been revoked."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

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

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

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/"
}

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

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

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