Push-Based Security Event Token (SET) Delivery Using HTTPAmazonrichanna@amazon.comMicrosoftmbj@microsoft.comhttp://self-issued.info/Coinbasemarius.scurtescu@coinbase.comCiscomorteza.ansari@cisco.comMicrosofttonynad@microsoft.com
Security
Security Events Working GroupInternet-Draft
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.
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:
The transmitter of the SET is capable of making outbound HTTP requests.
The recipient is capable of hosting an HTTP endpoint that is accessible
to the transmitter.
The transmitter and recipient are known to one another.
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 specification.
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
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 :
"Security Event Token (SET)", "SET Issuer", "SET Recipient", and "Event Payload".
This specification utilizes terminology defined in ,
as well as the terms defined below:
An entity that delivers SETs in its possession to one or more SET
Recipients.
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).
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 whitelisted
by the SET Recipient).
The SET Recipient is willing to accept the SET when transmitted
by the SET Transmitter (e.g., the SET Transmitter is expected to
send SETs with the 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 and issuer and
audience identification are defined in .
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 ).
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 ).
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 , 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.
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 ).
The body of the response MUST be empty.
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
SHOULD respond with an appropriate HTTP Status Code as defined in
Section 6 of .
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 ).
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 . 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 .
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 .The following table presents the initial set of Error Codes that are registered
in the IANA "Security Event Token Delivery Error Codes" registry:Error CodeDescriptioninvalid_requestThe request body cannot be parsed as a SET, or the
Event Payload within the SET does not conform to the event's definition.invalid_keyOne 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_failedThe SET Recipient could not authenticate the
SET Transmitter from the contents of the request.access_deniedThe 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
.
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 and
Security Considerations). This enables the SET Recipient
to validate that the SET Transmitter is authorized to deliver the SET.
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 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 .
Implementation security considerations for TLS can be found in
"Recommendations for Secure Use of TLS and DTLS" .
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 Recipient SHOULD ensure that such SETs have been signed in
accordance with .
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.
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 . Future assignments
are to be made through the First Come First Served registration policy ()
and shall follow the template presented in .
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).
The name of the Security Event Token Delivery Error Code, as described
in . 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.
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.
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.
Error Code: invalid_requestDescription: 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 GroupDefining Document(s):
of this document
Error Code: invalid_keyDescription: 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 GroupDefining Document(s):
of this document
Error Code: authentication_failedDescription: The SET Recipient could not authenticate the SET Transmitter
from the contents of the request.Change Controller: IETF Secevent Working GroupDefining Document(s):
of this document
Error Code: access_deniedDescription: The SET Transmitter is not authorized to transmit the
SET to the SET Recipient.Change Controller: IETF Secevent Working GroupDefining Document(s):
of this document
[[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 HTTPIn 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:XMPP EventsThe 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 ServiceSimple 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:API Reference: http://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/Welcome.htmlVisibility Timeouts: http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-visibility-timeout.htmlApache KafkaApache 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/introGoogle Pub/SubGoogle Pub Sub system favours a model whereby polling and acknowledgement
of events is done as separate endpoints as separate functions.Information:Cloud Overview - https://cloud.google.com/pubsub/Subscriber Overview - https://cloud.google.com/pubsub/docs/subscriberSubscriber Pull(poll) - https://cloud.google.com/pubsub/docs/pullThe 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:Renamed to "Push-Based SET Token Delivery Using HTTP"Removed references to the HTTP Polling delivery method.Removed informative reference to RFC6202.
Draft 01 - AB:
Fixed area and workgroup to match secevent.Removed unused definitions and definitions already covered by SET.Renamed Event Transmitter and Event Receiver to SET Transmitter and SET Receiver, respectively.Added IANA registry for SET Delivery Error Codes.Removed enumeration of HTTP authentication methods.Removed generally applicable guidance for HTTP, authorization tokens, and bearer tokens.Moved guidance for using authentication methods as DoS protection to Security Considerations.Removed redundant instruction to use WWW-Authenticate header.Removed further generally applicable guidance for authorization tokens.Removed bearer token from example delivery request, and text referencing it.Broke delivery method description into separate request/response sections.Added missing empty line between headers and body in example request.Removed unapplicable notes about example formatting.Removed text about SET creation and handling.Removed duplication in protocol description.Added "non-normative example" text to example transmission request.Fixed inconsistencies in use of Error Code term.
Draft 02 - AB:
Rewrote abstract and introduction.Rewrote definitions for SET Transmitter, SET Receiver.Renamed Event Delivery section to SET Delivery.Readability edits to Success Response and Failure Response sections.Consolidated definition of error response under Failure Response section.Removed Event Delivery Process section and moved its content to parent section.Readability edits to SET Delivery section and its subsections.Added callout that SET Receiver HTTP endpoint configuration is out-of-scope.Added callout that SET verification mechanisms are out-of-scope.Added retry guidance, notes regarding delivery reliability requirements.Added guidance around using JWS and/or JWE to authenticate persisted SETs.
Draft 03 - mbj:
Addressed problems identified in my 18-Jul-18 review message titled
"Issues for both the Push and Poll Specs".
Changes to align terminology with RFC 8417, for instance,
by using the already defined term SET Recipient rather than SET Receiver.
Applied editorial and minor normative corrections.
Updated Marius' contact information.
Draft 04 - AB:
Replaced Error Codes with smaller set of meaningfully differentiated codes.Added more error response examples.Removed un-referenced normative references.Added normative reference to JSON in error response definition.
Added text clarifying that the value of the description
attribute in error responses is implementation specific.
Added requirement that error descriptions and responses are UTF-8 encoded.
Added error description language preferences and specification via Accept-Language
and Content-Language headers.
Added "recognized issuer" validation requirement in section 2.Added time outs as an acceptable reason to resend a SET in section 2.Edited text in section 1 to clarify that configuration is out of scope.Made minor editorial corrections.
Draft 05 - AB:
Made minor editorial corrections.Updated example request with a correct SET header and signature.Revised TLS guidance to allow implementers to provide confidentiality protection via JWE.Revised TLS guidance to require *at least* TLS 1.2.Revised TLS guidance to recommend supporting the newest version of TLS that meets security requirements.Revised SET Delivery Error Code format to allow the same set of characters as is allowed in error codes in RFC6749.Added mention of HTTP Poll spec to list of other streaming specs in appendix.Added validation step requiring SET Recipient to verify that the SET is one which the SET Transmitter is expected to send to the SET Recipient.Changed responding to errors with an appropriate HTTP status code from optional to recommended.Changed Error Codes registry change policy from Expert Review to First Come First Served; added guidance that error codes are meant to be consumed by automated systems.Added text making clear that it is up to SET Recipients whether or not they will accept SETs where the SET Issuer is different from the SET Transmitter.Reworded guidance around signing and/or encrypting SETs for integrity protection.Renamed TLS "Support Considerations" section to "Confidentiality of SETs".Reworded guidance around subject identifier selection and privacy concerns.
Draft 06 - mbj, MS:
Made minor editorial corrections.Updated to indicate that failure response should be returned if errors occur in authenticating the SET.Updated reference for JSON from RFC 7159 to RFC 8259.Fixed Authentication Using Signed SETs to indicate the SET Transmitter must be authorized to deliver the SET, not the SET Issuer.Fixed Authenticating Persisted SETs to put the responsibility for ensuring the SET is signed on the SET Recipient.Fixed error code format definition to match error codes defined in doc.
Draft 07 - AB:
Made minor editorial corrections.Removed "SET Recipient" definition and added explicit list of terms used from RFC8417.