| Security Events Working Group | A. Backman, Ed. |
| Internet-Draft | Amazon |
| Intended status: Standards Track | M. Jones, Ed. |
| Expires: July 28, 2019 | Microsoft |
| M. Scurtescu | |
| Coinbase | |
| M. Ansari | |
| Cisco | |
| A. Nadalin | |
| Microsoft | |
| January 24, 2019 |
Push-Based Security Event Token (SET) Delivery Using HTTP
draft-ietf-secevent-http-push-04
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.
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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 receipt is out of scope for this specifications.
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 documents all figures may contain spaces and extra line-wrapping for readability and due to space limitations.
This specification utilizes terminology defined in [RFC8417], as well as the terms 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 and issuer and audience identification are defined in [RFC8417]. The mechanism for validating the authenticity of a SET is implementation specific, and may vary depending on the authentication mechanisms in use, and whether the SET is signed and/or encrypted (See Section 3).
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, or a decryption failure that may be due to misconfigured keys on the SET Recipient's side). 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 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 may be implementation-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 eyJhbGciOiJub25lIn0 . eyJwdWJsaXNoZXJVcmkiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20iLCJmZWV kVXJpcyI6WyJodHRwczovL2podWIuZXhhbXBsZS5jb20vRmVlZHMvOThkNTI0Nj FmYTViYmM4Nzk1OTNiNzc1NCIsImh0dHBzOi8vamh1Yi5leGFtcGxlLmNvbS9GZ WVkcy81ZDc2MDQ1MTZiMWQwODY0MWQ3Njc2ZWU3Il0sInJlc291cmNlVXJpcyI6 WyJodHRwczovL3NjaW0uZXhhbXBsZS5jb20vVXNlcnMvNDRmNjE0MmRmOTZiZDZ hYjYxZTc1MjFkOSJdLCJldmVudFR5cGVzIjpbIkNSRUFURSJdLCJhdHRyaWJ1dG VzIjpbImlkIiwibmFtZSIsInVzZXJOYW1lIiwicGFzc3dvcmQiLCJlbWFpbHMiX SwidmFsdWVzIjp7ImVtYWlscyI6W3sidHlwZSI6IndvcmsiLCJ2YWx1ZSI6Impk b2VAZXhhbXBsZS5jb20ifV0sInBhc3N3b3JkIjoibm90NHUybm8iLCJ1c2VyTmF tZSI6Impkb2UiLCJpZCI6IjQ0ZjYxNDJkZjk2YmQ2YWI2MWU3NTIxZDkiLCJuYW 1lIjp7ImdpdmVuTmFtZSI6IkpvaG4iLCJmYW1pbHlOYW1lIjoiRG9lIn19fQ . c2lnbmF0dXJl
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
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.
In the event of a general HTTP error condition, the SET Recipient MAY respond with an appropriate HTTP Status Code as defined in Section 6 of [RFC7231].
When the SET Recipient detects an error parsing or validating 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:
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 Transmitter is not permitted to transmit SETs issued by the issuer specified in the SET.
HTTP/1.1 400 Bad Request
Content-Language: en-US
Content-Type: application/json
{
"err": "access_denied",
"description": "Not authorized for issuer http://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. (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. |
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.
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.
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 issuer is authorized to deliver the SET.
SETs may contain sensitive information that is considered PII (e.g., subject claims). In such cases, SET Transmitters and SET Recipients MUST require the use of a transport-layer security mechanism. Event delivery endpoints MUST support TLS 1.2 [RFC5246] and MAY support additional transport-layer mechanisms meeting 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].
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.
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 Transmitter SHOULD sign the SET in accordance with [RFC7515] and optionally also encrypt it in accordance with [RFC7516].
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.
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.
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 Expert Review registration policy ([RFC8126]) and shall follow the template presented in Section 7.1.1.
| [RFC7235] | Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Authentication", RFC 7235, DOI 10.17487/RFC7235, June 2014. |
[[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:
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: https://kafka.apache.org/intro
Google Pub/Sub
Google Pub Sub system favours a model whereby polling and acknowledgement of events is done as separate endpoints 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.
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.
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: