| Security Events Working Group | A. Backman, Ed. |
| Internet-Draft | Amazon |
| Intended status: Standards Track | M. Jones, Ed. |
| Expires: December 26, 2020 | Microsoft |
| M. Scurtescu | |
| Coinbase | |
| M. Ansari | |
| Cisco | |
| A. Nadalin | |
| Microsoft | |
| June 24, 2020 |
Push-Based Security Event Token (SET) Delivery Using HTTP
draft-ietf-secevent-http-push-13
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.
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This Internet-Draft will expire on December 26, 2020.
Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved.
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This specification defines a mechanism by which a transmitter of a Security Event Token (SET) can deliver the SET to an intended SET Recipient via HTTP POST over TLS. This is an alternative SET delivery method to the one defined in [I-D.ietf-secevent-http-poll].
Push-based SET delivery over HTTP POST is intended for scenarios where all of the following apply:
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].
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.
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:
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, 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, 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. 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 re-transmit a SET if the responses from previous transmissions timed out or indicated potentially recoverable errors (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).
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 JWT.
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
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
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 object containing the following name/value pairs:
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)
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:
| 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. |
Other Error Codes may also be received, as the set of Error Codes is extensible via the IANA "Security Event Token Delivery Error Codes" registry established in Section 7.1.
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 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.
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 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 the reliability requirements of their use cases and the impact of various retry mechanisms on the performance of their systems to determine an appropriate strategy for handling various error conditions.
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.
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.
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 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 TLS and DTLS" [RFC7525] MUST be followed.
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.
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.
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.
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 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, 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).
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.
| [I-D.ietf-secevent-http-poll] | Backman, A., Jones, M., Scurtescu, M., Ansari, M. and A. Nadalin, "Poll-Based Security Event Token (SET) Delivery Using HTTP", Internet-Draft draft-ietf-secevent-http-poll-11, June 2020. |
| [RFC7235] | Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Authentication", RFC 7235, DOI 10.17487/RFC7235, June 2014. |
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 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.
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.)
[[ NOTE TO THE RFC EDITOR: This section to be removed prior to publication ]]
The following pub/sub, queuing, and 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 [I-D.ietf-secevent-http-poll] describes it as:
This specification defines how a series of Security Event Tokens (SETs) can be delivered to an intended recipient using HTTP POST over TLS initiated as a poll by the recipient. The specification also defines how delivery can be assured, subject to the SET Recipient's need for assurance.
XMPP Events
The WG considered XMPP Events and their 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 too 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 does not 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 am 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 that 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: https://kafka.apache.org/intro
Google Pub/Sub
The Google Pub Sub system favors a model whereby polling and acknowledgement of events is done with separate endpoints and as separate functions.
Information:
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.
[[ NOTE TO THE RFC EDITOR: This section to be removed prior to publication ]]
Draft 00 - AB - Based on draft-ietf-secevent-delivery-02 with the following changes:
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Draft 02 - AB:
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Draft 06 - mbj, MS:
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Draft 08 - mbj
Draft 09 - mbj + AB
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