Push-Based SET Token Delivery Using HTTP
draft-ietf-secevent-http-push-00

Abstract

This specification defines how a series of security event tokens (SETs) may be delivered to a previously registered receiver using HTTP POST over TLS initiated as a push to the receiver.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on October 18, 2018.

Copyright Notice

Copyright (c) 2018 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
• 1.1. Notational Conventions
• 1.2. Definitions
• 2. SET Event Stream Protocol
• 2.1. Event Delivery Process
• 2.2. Push Delivery using HTTP
• 2.3. Error Response Handling
• 3. Authentication and Authorization
• 3.1. Use of Tokens as Authorizations
• 4. Security Considerations
• 4.1. Authentication Using Signed SETs
• 4.2. HTTP Considerations
• 4.3. TLS Support Considerations
• 4.4. Authorization Token Considerations
• 4.4.1. Bearer Token Considerations
• 5. Privacy Considerations
• 6. IANA Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Appendix A. Other Streaming Specifications
• Appendix B. Acknowledgments
• Appendix C. Change Log
• Authors' Addresses

1. Introduction and Overview

This specification defines how a stream of SETs (see [I-D.ietf-secevent-token]) can be transmitted to a previously registered Event Receiver using HTTP [RFC7231] over TLS. The specification defines a method to push SETs via HTTP POST.

This specification defines a method for SET delivery in what is known as Event Streams.

This specification does not define the method by which Event Streams are defined, provisioned, managed, monitored, and configured and is out of scope of this specification.
[[This work is TBD by the SECEVENTS WG]]

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.

For purposes of readability examples are not URL encoded. Implementers MUST percent encode URLs as described in Section 2.1 of .

Throughout this documents all figures MAY contain spaces and extra line-wrapping for readability and space limitations. Similarly, some URI's contained within examples, have been shortened for space and readability reasons.

1.2. Definitions

This specification assumes terminology defined in the Security Event Token specification[I-D.ietf-secevent-token] .

The following definitions are defined for Security Event distribution:

Event Transmitter

A service provider that delivers SETs to other providers known as Event Receivers. An Event Transmitter is responsible for offering a service that allows the Event Receiver to check the Event Stream configuration and status known as the "Control Plane".

Event Receiver

A service provider that registers to receive SETs from an Event Transmitter and provides an endpoint to receive SETs via HTTP POST. Event Receivers can check current Event Stream configuration and status by accessing the Event Transmitters "Control Plane".

Event Stream

An Event Stream is a defined location, distribution method and whereby an Event Transmitter and Event Receiver exchange a pre-defined family of SETs. A Stream is assumed to have configuration data such as HTTP endpoints, timeouts, public key sets for signing and encryption, and Event Families.

Subject

The security subject around which a security event has occurred. For example, a security subject might per a user, a person, an email address, a service provider entity, an IP address, an OAuth Client, a mobile device, or any identifiable thing referenced in security and authorization systems.

Event

An Event is defined to be an event as represented by a security event token (SET). See [I-D.ietf-secevent-token].

NumericDate

A JSON numeric value representing the number of seconds from 1970-01-01T00:00:00Z UTC until the specified UTC date/time, ignoring leap seconds. This is equivalent to the IEEE Std 1003.1, 2013 Edition [POSIX.1] definition "Seconds Since the Epoch", in which each day is accounted for by exactly 86400 seconds, other than that non-integer values can be represented. See [RFC3339] for details regarding date/times in general and UTC in particular.

2. SET Event Stream Protocol

An Event Stream represents the communication channel over which a series of SETs are delivered to a configured Event Receiver.

2.1. Event Delivery Process

When an Event occurs, the Event Transmitter constructs a SET token [I-D.ietf-secevent-token] that describes the Event. The Event Transmitter determines the Event Streams over which the SET should be distributed to.

How SETs are defined and the process by which Events are identified for Event Receivers is out-of-scope of this specification.

When a SET is available for an Event Receiver, the Event Transmitter attempts to deliver the SET based on the Event Receiver's registered delivery mechanism:

• The Event Transmitter uses an HTTP/1.1 POST to the Event Receiver endpoint to deliver the SET;
• Or, the Event Transmitter delivers the Event through a different method not defined by this specification.

In Push-Based SET Delivery Using HTTP, SETs are delivered one at a time using HTTP POST requests by an Event Transmitter to an Event Receiver. The HTTP request body is a JSON Web Token [RFC7519] with a Content-Type header of application/secevent+jwt as defined in Section 2.2 and 6.2 of [I-D.ietf-secevent-token]. Upon receipt, the Event Receiver acknowledges receipt with a response with HTTP Status 202, as described below in Section 2.2.

After successful (acknowledged) SET delivery, Event Transmitters SHOULD NOT be required to maintain or record SETs for recovery. Once a SET is acknowledged, the Event Receiver SHALL be responsible for retention and recovery.

Transmitted SETs SHOULD be self-validating (e.g. signed) if there is a requirement to verify they were issued by the Event Transmitter at a later date when de-coupled from the original delivery where authenticity could be checked via the HTTP or TLS mutual authentication.

Upon receiving a SET, the Event Receiver reads the SET and validates it. The Event Receiver MUST acknowledge receipt to the Event Transmitter, using the defined acknowledgement or error method.

The Event Receiver SHALL NOT use the Event acknowledgement mechanism to report Event errors other than relating to the parsing and validation of the SET.

2.2. Push Delivery using HTTP

This method allows an Event Transmitter to use HTTP POST (Section 4.3.3) to deliver SETs to a previously registered web callback URI supplied by the Event Receiver as part of an Event Stream configuration process (not defined by this document).

The SET to be delivered MAY be signed and/or encrypted as defined in [I-D.ietf-secevent-token].

The Event Stream configuration defines a URI of an Event Receiver provided endpoint which accepts HTTP POST requests (e.g. https://rp.example.com/Events).

The HTTP Content-Type (see Section 3.1.1.5) for the HTTP POST is application/secevent+jwt and SHALL consist of a single SET (see [I-D.ietf-secevent-token]). As per Section 5.3.2, the expected media type (Accept header) response is application/json.

To deliver an Event, the Event Transmitter generates an event delivery message and uses HTTP POST to the configured endpoint with the appropriate Accept and Content-Type headers.

POST /Events  HTTP/1.1

Host: notify.examplerp.com
Accept: application/json
Authorization: Bearer h480djs93hd8
Content-Type: application/secevent+jwt
eyJhbGciOiJub25lIn0
.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.

Figure 1: Example HTTP POST Request

Upon receipt of the request, the Event Receiver SHALL validate the JWT structure of the SET as defined in Section 7.2. The Event Receiver SHALL also validate the SET information as described in Section 2.

If the SET is determined to be valid, the Event Receiver SHALL "acknowledge" successful submission by responding with HTTP Status 202 as Accepted (see Section 6.3.3).

In order to maintain compatibility with other methods of transmission, the Event Receiver SHOULD NOT include an HTTP response body representation of the submitted SET or what the SET's pending status is when acknowledging success. In the case of an error (e.g. HTTP Status 400), the purpose of the HTTP response body is to indicate any SET parsing, validation, or cryptographic errors.

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 Event Transmitter know that a SET has been delivered and the information no longer needs to be retained by the Event Transmitter. Before acknowledgement, Event Receivers 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 Event Receivers is out-of-scope of this specification.

In the Event of a general HTTP error condition, the Event Receiver MAY respond with an appropriate HTTP Status code as defined in Section 6.

When the Event Receiver detects an error parsing or validating a received SET (as defined by [I-D.ietf-secevent-token]), the Event Receiver SHALL indicate an HTTP Status 400 error with an error code as described in Section 2.3.

The following is an example non-normative error response.

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

{
  "err":"dup",
  "description":"SET already received. Ignored."

}

Figure 3: Example HTTP Status 400 Response

2.3. Error Response Handling

If a SET is invalid, the following error codes are defined:

An error response SHALL include a JSON object which provides details about the error. The JSON object includes the JSON attributes: Figure 3).

err

A value which is a keyword that describes the error (see Table 1).

description

A human-readable text that provides additional diagnostic information.

When included as part of an HTTP Status 400 response, the above JSON is the HTTP response body (see

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]. For example, the following methodologies could be used among others:

TLS Client Authentication

Event delivery endpoints MAY request TLS mutual client authentication. See Section 7.3.

Bearer Tokens

Bearer tokens [RFC6750] MAY be used when combined with TLS and a token framework such as OAuth 2.0 [RFC6749]. For security considerations regarding the use of bearer tokens in SET delivery see Section 4.4.1.

Basic Authentication

Usage of basic authentication should be avoided due to its use of a single factor that is based upon a relatively static, symmetric secret. Implementers SHOULD combine the use of basic authentication with other factors. The security considerations of HTTP BASIC, are well documented in [RFC7617] and SHOULD be considered along with using signed SETs (see SET Payload Authentication below).

SET Payload Authentication

In scenarios where SETs are signed and the delivery method is HTTP POST (see Section 2.2), Event Receivers MAY elect to use Basic Authentication or not to use HTTP or TLS based authentication at all. See Section 4.1 for considerations.

As per Section 4.1 of, a SET delivery endpoint SHALL indicate supported HTTP authentication schemes via the WWW-Authenticate header.

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 an authentication method above. This specification considers authentication as a feature to prevent denial-of-service attacks. Because SETs are not commands (see ), Event Receivers are free to ignore SETs that are not of interest.

For illustrative purposes only, SET delivery examples show an OAuth2 bearer token value [RFC6750] in the authorization header. This is not intended to imply that bearer tokens are preferred. However, the use of bearer tokens in the specification does reflect common practice.

3.1. Use of Tokens as Authorizations

When using bearer tokens or proof-of-possession tokens that represent an authorization grant such as issued by OAuth (see [RFC6749]), implementers SHOULD consider the type of authorization granted, any authorized scopes (see Section 3.3 of [RFC6749]), and the security subject(s) that SHOULD be mapped from the authorization when considering local access control rules. Section 6 of the OAuth Assertions draft [RFC7521], documents common scenarios for authorization including:[RFC7521]). When using other token formats or frameworks, implementers MUST take into account similar threats and countermeasures, especially those documented by the relevant specifications.

• Clients using an assertion to authenticate and/or act on behalf of itself;
• Clients acting on behalf of a user; and,
• A Client acting on behalf of an anonymous user (e.g., see next section).

When using OAuth authorization tokens, implementers MUST take into account the threats and countermeasures documented in the security considerations for the use of client authorizations (see Section 8 of

4. Security Considerations

4.1. 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 Event Receiver to validate that the SET issuer is authorized to deliver SETs.

4.2. HTTP Considerations

SET delivery depends on the use of Hypertext Transfer Protocol and thus subject to the security considerations of HTTP Section 9 and its related specifications.

As stated in Section 2.7.1, an HTTP requestor MUST NOT generate the userinfo (i.e., username and password) component (and its "@" delimiter) when an "http" URI reference is generated with a message as they are now disallowed in HTTP.

4.3. TLS Support Considerations

SETs contain sensitive information that is considered PII (e.g. subject claims). Therefore, Event Transmitters and Event Receivers 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].

4.4. Authorization Token Considerations

When using authorization tokens such as those issued by OAuth 2.0 [RFC6749], implementers MUST take into account threats and countermeasures documented in Section 8 of [RFC7521].

4.4.1. Bearer Token Considerations

Due to the possibility of interception, Bearer tokens MUST be exchanged using TLS.

Bearer tokens MUST have a limited lifetime that can be determined directly or indirectly (e.g., by checking with a validation service) by the service provider. By expiring tokens, clients are forced to obtain a new token (which usually involves re-authentication) for continued authorized access. For example, in OAuth2, a client MAY use OAuth token refresh to obtain a new bearer token after authenticating to an authorization server. See Section 6 of [RFC6749].

Implementations supporting OAuth bearer tokens need to factor in security considerations of this authorization method [RFC7521]. Since security is only as good as the weakest link, implementers also need to consider authentication choices coupled with OAuth bearer tokens. The security considerations of the default authentication method for OAuth bearer tokens, HTTP BASIC, are well documented in [RFC7617], therefore implementers are encouraged to prefer stronger authentication methods. Designating the specific methods of authentication and authorization are out-of-scope for the delivery of SET tokens, however this information is provided as a resource to implementers.

5. Privacy Considerations

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

Event Transmitters SHOULD attempt to specialize Event Streams so that the content is 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, Event Transmitters and Receivers 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, Event Transmitters and Receivers SHOULD devise approaches that prevent propagation -- for example, the passing of a hash value that requires the subscriber to already know the subject.

6. IANA Considerations

There are no IANA considerations.

7. References

7.1. Normative References

7.2. Informative References

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:

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:

• API Reference: http://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/Welcome.html
• Visibility Timeouts: http://docs.aws.amazon.com/AWSSimpleQueueService/latest/SQSDeveloperGuide/sqs-visibility-timeout.html

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:

• Cloud Overview - https://cloud.google.com/pubsub/
• Subscriber Overview - https://cloud.google.com/pubsub/docs/subscriber
• Subscriber Pull(poll) - https://cloud.google.com/pubsub/docs/pull

Appendix B. Acknowledgments

The editors would like to thanks the members of the SCIM WG which began discussions of provisioning events starting with: draft-hunt-scim-notify-00 in 2015.

The editors would like to thank the authors of draft-ietf-secevent-delivery-02, on which this draft is based.

The editor would like to thank the participants in the the SECEVENTS working group for their support of this specification.

Appendix C. Change Log

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.

Authors' Addresses