Security Event Token (SET)
draft-ietf-secevent-token-02

Security Events Working Group                               P. Hunt, Ed.
Internet-Draft                                                    Oracle
Intended status: Standards Track                              W. Denniss
Expires: January 1, 2018                                          Google
                                                               M. Ansari
                                                                   Cisco
                                                                M. Jones
                                                               Microsoft
                                                           June 30, 2017

                       Security Event Token (SET)
                      draft-ietf-secevent-token-02

Abstract

   This specification defines the Security Event Token, which may be
   distributed via a protocol such as HTTP.  The Security Event Token
   (SET) specification profiles the JSON Web Token (JWT), which can be
   optionally signed and/or encrypted.  A SET describes a statement of
   fact from the perspective of an issuer that it intends to share with
   one or more receivers.

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
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   Drafts is at http://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 January 1, 2018.

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) in effect on the date of

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   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 . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  The Security Event Token (SET)  . . . . . . . . . . . . . . .   5
     2.1.  Core SET Claims . . . . . . . . . . . . . . . . . . . . .   8
     2.2.  Explicit Typing of SETs . . . . . . . . . . . . . . . . .  10
     2.3.  Security Event Token Construction . . . . . . . . . . . .  10
   3.  Requirements for SET Profiles . . . . . . . . . . . . . . . .  12
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
     4.1.  Confidentiality and Integrity . . . . . . . . . . . . . .  13
     4.2.  Delivery  . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.3.  Sequencing  . . . . . . . . . . . . . . . . . . . . . . .  13
     4.4.  Timing Issues . . . . . . . . . . . . . . . . . . . . . .  14
     4.5.  Distinguishing SETs from ID Tokens  . . . . . . . . . . .  14
     4.6.  Distinguishing SETs from Access Tokens  . . . . . . . . .  15
     4.7.  Distinguishing SETs from other kinds of JWTs  . . . . . .  15
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  16
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     6.1.  JSON Web Token Claims Registration  . . . . . . . . . . .  16
       6.1.1.  Registry Contents . . . . . . . . . . . . . . . . . .  17
     6.2.  Media Type Registration . . . . . . . . . . . . . . . . .  17
       6.2.1.  Registry Contents . . . . . . . . . . . . . . . . . .  17
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  18
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  20
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction and Overview

   This specification defines an extensible Security Event Token (SET)
   format which may be exchanged using protocols such as HTTP.  The
   specification builds on the JSON Web Token (JWT) format [RFC7519] in
   order to provide a self-contained token that can be optionally signed
   using JSON Web Signature (JWS) [RFC7515] and/or encrypted using JSON
   Web Encryption (JWE) [RFC7516].

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   This specification profiles the use of JWT for the purpose of issuing
   security event tokens (SETs).  This specification defines a base
   format upon which profiling specifications define actual events and
   their meanings.  Unless otherwise specified, this specification uses
   non-normative example events intended to demonstrate how events may
   be constructed.

   This specification is scoped to security and identity related events.
   While security event tokens may be used for other purposes, the
   specification only considers security and privacy concerns relevant
   to identity and personal information.

   Security Events are not commands issued between parties.  A security
   event is a statement of fact from the perspective of an issuer about
   the state of a security subject (e.g., a web resource, token, IP
   address, the issuer itself) that the issuer controls or is aware of,
   that has changed in some way (explicitly or implicitly).  A security
   subject MAY be permanent (e.g., a user account) or temporary (e.g.,
   an HTTP session) in nature.  A state change could describe a direct
   change of entity state, an implicit change of state or other higher-
   level security statements such as:

   o  The creation, modification, removal of a resource.

   o  The resetting or suspension of an account.

   o  The revocation of a security token prior to its expiry.

   o  The logout of a user session.  Or,

   o  A cumulative conclusion such as to indicate that a user has taken
      over an email identifier that may have been used in the past by
      another user.

   While subject state changes are often triggered by a user-agent or
   security-subsystem, the issuance and transmission of an event often
   occurs asynchronously and in a back-channel to the action which
   caused the change that generated the security event.  Subsequently,
   an Event Receiver, having received a SET, validates and interprets
   the received SET and takes its own independent actions, if any.  For
   example, having been informed of a personal identifier being
   associated with a different security subject (e.g., an email address
   is being used by someone else), the Event Receiver may choose to
   ensure that the new user is not granted access to resources
   associated with the previous user.  Or, the Event Receiver may not
   have any relationship with the subject, and no action is taken.

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   While Event Receivers will often take actions upon receiving SETs,
   security events MUST NOT be assumed to be commands or requests.  The
   intent of this specification is to define a way of exchanging
   statements of fact that subscribers may interpret for their own
   purposes.  As such, SETs have no capability for error signaling other
   to ensure the validation of a received SET.

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
   [RFC2119].  These keywords are capitalized when used to unambiguously
   specify requirements of the protocol or application features and
   behavior that affect the inter-operability and security of
   implementations.  When these words are not capitalized, they are
   meant in their natural-language sense.

   For purposes of readability, examples are not URL encoded.
   Implementers MUST percent encode URLs as described in Section 2.1 of
   [RFC3986].

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

1.2.  Definitions

   The following definitions are used with SETs:

   Security Event Token (SET)
      A SET is a JWT [RFC7519] that is distributed to one or more
      registered Event Receivers.

   Event Transmitter
      A service provider that delivers SETs to other providers known as
      Event Receivers.

   Event Receiver
      An Event Receiver is an entity that receives SETs through some
      distribution method.

   Subject
      A SET describes an event or state change that has occurred about a
      Subject.  A Subject may be a principal (e.g., Section 4.1.2
      [RFC7519]), a web resource, an entity such as an IP address, or
      the issuer itself that a SET might reference.

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   Profiling Specification  A specification that uses the SET Token
      specification to define one or more event types and the associated
      claims included.

2.  The Security Event Token (SET)

   A SET is a data structure (in the form of a JWT [RFC7519])
   representing one or more related security events about a Subject.

   The schema and structure of a SET follows the JWT [RFC7519]
   specification.  A SET has the following structure:

   o  An outer JSON object that acts as the SET "envelope".  The
      envelope contains a set of name/value pairs called the JWT Claims
      Set, typically common to every SET or common to a number of
      different Events within a single Profiling Specification or a
      related series of specifications.  Claims in the envelope (the
      outer JSON structure) SHOULD be registered in the JWT Token Claims
      Registry Section 10.1 [RFC7519] or be Public Claims or Private
      Claims as also defined in [RFC7519].

   o  Envelope claims that are profiled and defined in this
      specification are used to validate a SET and declare the contents
      of the event data included in the SET.  The claim "events"
      identifies the event types expressed that are related to the
      Security Subject and MAY also include event-specific data.

   o  Each JSON member of the "events" object is a name and value pair.
      The JSON attribute name is a URI String value that expresses an
      event type, and the corresponding value is a JSON object known as
      the event "payload".  The payload JSON object contains claims
      typically unique to the event's URI type value and are not
      registered as JWT claims.  These claims are defined by their
      associated Profiling Specification.  An event with no payload
      claims SHALL be represented as the empty JSON object ("{}").  In
      many cases, one event URI expresses the primary event URI, while
      other events might be considered extensions that MAY be used to do
      things such as:

      *  A categorization event type to provide classification
         information (e.g., threat type or level).

      *  An enhancement of an existing specifications the arise over
         time.

      *  An extension needed to link a potential series of events.

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      *  Localized specific purpose event URI used between a particular
         Event Transmitter and Receiver.

   The following is a non-normative example showing the JWT Claims Set
   for a hypothetical SCIM password reset SET.  This example shows an
   additional events value ("https://example.com/scim/event/
   passwordResetExt") used to convey additional information -- in this
   case, the current count of reset attempts:

   {
     "jti": "3d0c3cf797584bd193bd0fb1bd4e7d30",
     "iat": 1458496025,
     "iss": "https://scim.example.com",
     "aud": [
       "https://jhub.example.com/Feeds/98d52461fa5bbc879593b7754",
       "https://jhub.example.com/Feeds/5d7604516b1d08641d7676ee7"
     ],
     "sub": "https://scim.example.com/Users/44f6142df96bd6ab61e7521d9",
     "events": {
       "urn:ietf:params:scim:event:passwordReset":
         { "id":"44f6142df96bd6ab61e7521d9"},
       "https://example.com/scim/event/passwordResetExt":
         { "resetAttempts":5}
     }
   }

                Figure 1: Example SCIM Password Reset Event

   The event in the figure above expresses hypothetical password reset
   event for SCIM [RFC7644].  The JWT consists of:

   o  An "events" claim specifying the hypothetical SCIM URN
      ("urn:ietf:params:scim:event:passwordReset") for a password reset,
      and a local schema, "https://example.com/scim/event/
      passwordResetExt", that is used to provide additional event
      information such as the current count of resets.

   o  An "iss" claim, denoting the Event Transmitter.

   o  The "sub" claim specifies the SCIM resource URI that was affected.

   o  The "aud" claim specifies the intended audiences for the event.
      The syntax of the "aud" claim is defined in Section 4.1.3
      [RFC7519].

   In this example, the SCIM event indicates that a password has been
   updated and the current password reset count is 5.  Notice that the

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   value for "resetAttempts" is actually part of its own JSON object
   associated with its own event URI attribute.

   Here is another example JWT Claims Set for a security event token,
   this one for a Logout Token:

   {
      "iss": "https://server.example.com",
      "sub": "248289761001",
      "aud": "s6BhdRkqt3",
      "iat": 1471566154,
      "jti": "bWJq",
      "sid": "08a5019c-17e1-4977-8f42-65a12843ea02",
      "events": {
        "http://schemas.openid.net/event/backchannel-logout": {}
      }
   }

            Figure 2: Example OpenID Back-Channel Logout Event

   Note that the above SET has an empty JSON object and uses the JWT
   registered claims "sub" and "sid" to identify the subject that was
   logged-out.

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   In the following example JWT Claims Set, a fictional medical service
   collects consent for medical actions and notifies other parties.  The
   individual for whom consent is identified was originally
   authenticated via OpenID Connect.  In this case, the issuer of the
   security event is an application rather than the OpenID provider:

   {
     "jti": "fb4e75b5411e4e19b6c0fe87950f7749",

     "sub": "248289761001",
     "iat": 1458496025,
     "iss": "https://my.examplemed.com",
     "aud": [
       "https://rp.example.com"
     ],
     "events": {
       "https://openid.net/heart/specs/consent.html":{
         "iss":"https://connect.example.com",
         "consentUri":[
           "https://terms.examplemed.com/labdisclosure.html#Agree"
         ]
       }
     }
   }

                      Figure 3: Example Consent Event

   In the above example, the attribute "iss" contained within the
   payload for the event "https://openid.net/heart/specs/consent.html"
   refers to the issuer of the Security Subject ("sub") rather than the
   event issuer "https://my.examplemed.com".  They are distinct from the
   top level value of "iss", which always refers to the issuer of the
   event - a medical consent service that is a relying party to the
   OpenID Provider.

2.1.  Core SET Claims

   The following are claims that are based on [RFC7519] claim
   definitions and are profiled for use in an event token:

   jti
      As defined by Section 4.1.7 [RFC7519] contains a unique identifier
      for an event.  The identifier SHOULD be unique within a particular
      event feed and MAY be used by clients to track whether a
      particular event has already been received.  This claim is
      REQUIRED.

   iss

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      A single valued String containing the URI of the service provider
      publishing the SET (the issuer).  This claim is REQUIRED.  Note
      that when a SET is expressing an event about a Security Subject
      for which the SET issuer is not the issuer of the Security
      Subject, the conflict SHALL be resolved by including the Security
      Subject "iss" value within the event "payload" (see "events"
      claim).

   aud
      The syntax of the claim is as defined in Section 4.1.3 [RFC7519].
      This claim contains one or more audience identifiers for the SET.
      This claim is RECOMMENDED.

   iat
      As defined by Section 4.1.6 [RFC7519], a value containing a
      NumericDate, which represents when the event was issued.  Unless
      otherwise specified, the value SHOULD be interpreted as equivalent
      to the actual time of the event.  This claim is REQUIRED.

   nbf
      Defined by Section 4.1.5 [RFC7519], a number whose value is a
      NumericDate.  In the context of the SET token it SHALL be
      interpreted to mean a date in which the event is believed to have
      occurred (in the past) or will occur in the future.  Note: there
      MAY be some cases where "nbf" is still smaller than "iat" such as
      when it took an extended time for a SET to be issued (for example
      after some analysis).  This claim is OPTIONAL.

   sub  As defined by Section 4.1.2 [RFC7519], a String or URI value
      representing the principal or the subject of the SET.  This is
      usually the entity whose "state" was changed.  For example, an IP
      Address was added to a black list.  A URI representing a user
      resource that was modified.  A token identifier for a revoked
      token.  If used, the Profile Specification SHOULD define the
      content and format semantics for the value.  This claim is
      OPTIONAL, as the principal for any given profile may already be
      identified without the inclusion of a subject claim.  Note that
      some SET profiles MAY choose to convey event subject information
      in the event payload, particularly if the subject information is
      relative to issuer information that is also conveyed in the event
      payload, which may be the case for some identity SET profiles.

   exp  As defined by [RFC7519], this claim is time on which the JWT
      MUST NOT be accepted for processing.  In the context of a SET
      however, this notion does not apply since a SET reflects something
      that has already been processed and is historical in nature.
      While some specifications MAY have a need for this claim, its use
      in general cases is NOT RECOMMENDED.

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   The following are new claims defined by this specification:

   events
      The semantics of this claim is to define a set of event statements
      that each MAY add additional claims to fully describe a single
      logical event that has occurred (e.g. a state change to a
      subject).  Multiple event statements of the same type SHALL NOT be
      accepted.  The "events" claim SHOULD NOT be used to express
      multiple logical events.

      The value of "events" is a JSON object whose members are a set of
      JSON name/value pairs whose names are URIs representing the event
      statements being expressed.  Event URI values SHOULD be stable
      values (e.g. a permanent URL for an event specification).  For
      each name present, the corresponding value SHALL be a JSON object.
      The JSON object MAY be an empty object ("{}"), or it MAY be a JSON
      object containing data as described by the Profiling
      Specification.

   txn
      An OPTIONAL String value that represents a unique transaction
      identifier.  In cases where multiple SETs are issued based on
      different event URIs, the transaction identifier MAY be used to
      correlate SETs to the same originating event or stateful change.

2.2.  Explicit Typing of SETs

   This specification registers the "application/secevent+jwt" media
   type, which can be used to indicate that the content is a SET.  SETs
   MAY include this media type in the "typ" header parameter of the JWT
   representing the SET to explicitly declare that the JWT is a SET.
   This MUST be included if the SET could be used in an application
   context in which it could be confused with other kinds of JWTs.

   Per the definition of "typ" in Section 4.1.9 of [RFC7515], it is
   RECOMMENDED that the "application/" prefix be omitted.  Therefore,
   the "typ" value used SHOULD be "secevent+jwt".

2.3.  Security Event Token Construction

   A SET is a JWT [RFC7519] that is constructed by building a JSON
   structure that constitutes an event object which is then used as the
   body of a JWT.

   While this specification uses JWT to convey a SET, implementers SHALL
   NOT use SETs to convey authentication or authorization assertions.

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   The following is an example JWT Claims Set for a security event token
   (which has been formatted for readability):

   {
     "jti": "4d3559ec67504aaba65d40b0363faad8",
     "iat": 1458496404,
     "iss": "https://scim.example.com",
     "aud": [
      "https://scim.example.com/Feeds/98d52461fa5bbc879593b7754",
      "https://scim.example.com/Feeds/5d7604516b1d08641d7676ee7"
     ],

     "events": {
       "urn:ietf:params:scim:event:create": {
         "ref":
           "https://scim.example.com/Users/44f6142df96bd6ab61e7521d9",
         "attributes":["id", "name", "userName", "password", "emails"]
       }
     }
   }

                      Figure 4: Example Event Claims

   When transmitted, the above JSON body must be converted into a JWT as
   per [RFC7519].

   The following is an example of a SCIM Event expressed as an unsecured
   JWT.  The JOSE Header is:

   {"typ":"secevent+jwt","alg":"none"}

   Base64url encoding of the octets of the UTF-8 representation of the
   JOSE Header yields:

   eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJub25lIn0

   The example JWT Claims Set is encoded as follows:

   eyJqdGkiOiI0ZDM1NTllYzY3NTA0YWFiYTY1ZDQwYjAzNjNmYWFkOCIsImlhdCI6MTQ1
   ODQ5NjQwNCwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwiYXVkIjpbImh0
   dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg3OTU5M2I3
   NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYwNDUxNmIxZDA4
   NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybjppZXRmOnBhcmFtczpzY2ltOmV2ZW50
   OmNyZWF0ZSI6eyJyZWYiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20vVXNlcnMvNDRm
   NjE0MmRmOTZiZDZhYjYxZTc1MjFkOSIsImF0dHJpYnV0ZXMiOlsiaWQiLCJuYW1lIiwi
   dXNlck5hbWUiLCJwYXNzd29yZCIsImVtYWlscyJdfX19

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   The encoded JWS signature is the empty string.  Concatenating the
   parts yields:

   eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJub25lIn0.
   eyJqdGkiOiI0ZDM1NTllYzY3NTA0YWFiYTY1ZDQwYjAzNjNmYWFkOCIsImlhdCI6MTQ1
   ODQ5NjQwNCwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwiYXVkIjpbImh0
   dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg3OTU5M2I3
   NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYwNDUxNmIxZDA4
   NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybjppZXRmOnBhcmFtczpzY2ltOmV2ZW50
   OmNyZWF0ZSI6eyJyZWYiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20vVXNlcnMvNDRm
   NjE0MmRmOTZiZDZhYjYxZTc1MjFkOSIsImF0dHJpYnV0ZXMiOlsiaWQiLCJuYW1lIiwi
   dXNlck5hbWUiLCJwYXNzd29yZCIsImVtYWlscyJdfX19.

             Figure 5: Example Unsecured Security Event Token

   For the purpose of a simpler example in Figure 5, an unsecured token
   was shown.  When SETs are not signed or encrypted, the Event Receiver
   MUST employ other mechanisms such as TLS and HTTP to provide
   integrity, confidentiality, and issuer validation, as needed by the
   application.

   When validation (i.e. auditing), or additional transmission security
   is required, JWS signing and/or JWE encryption MAY be used.  To
   create and or validate a signed and/or encrypted SET, follow the
   instructions in Section 7 of [RFC7519].

3.  Requirements for SET Profiles

   Profile Specifications for SETs define the syntax and semantics of
   SETs conforming to that SET profile and rules for validating those
   SETs.  The syntax defined by profiling specifications includes what
   claims and event payload values are used by SETs utilizing the
   profile.

   Defining the semantics of the SET contents for SETs utilizing the
   profile is equally important.  Possibly most important is defining
   the procedures used to validate the SET issuer and to obtain the keys
   controlled by the issuer that were used for cryptographic operations
   used in the JWT representing the SET.  For instance, some profiles
   may define an algorithm for retrieving the SET issuer's keys that
   uses the "iss" claim value as its input.

   Profile Specifications MUST clearly specify the steps that a
   recipient of a SET utilizing that profile MUST perform to validate
   that the SET is both syntactically and semantically valid.

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4.  Security Considerations

4.1.  Confidentiality and Integrity

   SETs may often contain sensitive information.  Therefore, methods for
   distribution of events SHOULD require the use of a transport-layer
   security mechanism when distributing events.  Parties 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].

   Security Events distributed through third-parties or that carry
   personally identifiable information, SHOULD be encrypted using JWE
   [RFC7516] or secured for confidentiality by other means.

   Security Events distributed without authentication over the channel,
   such as via TLS ([RFC5246] and [RFC6125]), and/or OAuth 2.0
   [RFC6749], or Basic Authentication [RFC7617], MUST be signed using
   JWS [RFC7515] so that individual events can be authenticated and
   validated by the Event Receiver.

4.2.  Delivery

   This specification does not define a delivery mechanism by itself.
   In addition to confidentiality and integrity (discussed above),
   implementers and Profile Specifications MUST consider the
   consequences of delivery mechanisms that are not secure and/or not
   assured.  For example, while a SET may be end-to-end secured using
   JWE encrypted SETs, without TLS there is no assurance that the
   correct endpoint received the SET and that it could be successfully
   processed.

4.3.  Sequencing

   As defined in this specification, there is no defined way to order
   multiple SETs in a sequence.  Depending on the type and nature of SET
   event, order may or may not matter.  For example, in provisioning,
   event order is critical -- an object could not be modified before it
   was created.  In other SET types, such as a token revocation, the
   order of SETs for revoked tokens does not matter.  If however, the
   event was described as a log-in or logged-out status for a user
   subject, then order becomes important.

   Profiling Specifications and implementers SHOULD take caution when
   using timestamps such as "iat" to define order.  Distributed systems

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   will have some amount of clock-skew and thus time by itself will not
   guarantee order.

   Specifications profiling SET SHOULD define a mechanism for detecting
   order or sequence of events.  For example, the "txn" claim could
   contain an ordered value (e.g., a counter) that the issuer defines.

4.4.  Timing Issues

   When SETs are delivered asynchronously and/or out-of-band with
   respect to the original action that incurred the security event, it
   is important to consider that a SET might be delivered to a
   Subscriber in advance or well behind the process that caused the
   event.  For example, a user having been required to logout and then
   log back in again, may cause a logout SET to be issued that may
   arrive at the same time as the user-agent accesses a web site having
   just logged-in.  If timing is not handled properly, the effect would
   be to erroneously treat the new user session as logged out.
   Profiling Specifications SHOULD be careful to anticipate timing and
   subject selection information.  For example, it might be more
   appropriate to cancel a "session" rather than a "user".
   Alternatively, the specification could use timestamps that allows new
   sessions to be started immediately after a stated logout event time.

4.5.  Distinguishing SETs from ID Tokens

   Because [RFC7519] states that "all claims that are not understood by
   implementations MUST be ignored", there is a consideration that a SET
   token might be confused with ID Token [OpenID.Core] if a SET is
   mistakenly or intentionally used in a context requiring an ID Token.
   If a SET could otherwise be interpreted as a valid ID Token (because
   it includes the required claims for an ID Token and valid issuer and
   audience claim values for an ID Token) then that SET profile MUST
   require that the "exp" claim not be present in the SET.  Because
   "exp" is a required claim in ID Tokens, valid ID Token
   implementations will reject such a SET if presented as if it were an
   ID Token.

   Excluding "exp" from SETs that could otherwise be confused with ID
   Tokens is actually defense in depth.  In any OpenID Connect contexts
   in which an attacker could attempt to substitute a SET for an ID
   Token, the SET would actually already be rejected as an ID Token
   because it would not contain the correct "nonce" claim value for the
   ID Token to be accepted in that context.

   Note that the use of explicit typing, as described in Section 2.2,
   will not achieve disambiguation between ID Tokens and SETs, as the ID
   Token validation rules do not use the "typ" header parameter value.

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4.6.  Distinguishing SETs from Access Tokens

   OAuth 2.0 [RFC6749] defines access tokens as being opaque.
   Nonetheless, some implementations implement access tokens as JWTs.
   Because the structure of these JWTs is implementation-specific,
   ensuring that a SET cannot be confused with such an access token is
   therefore likewise, in general, implementation specific.
   Nonetheless, it is recommended that SET profiles employ the following
   strategies to prevent possible substitutions of SETs for access
   tokens in contexts in which that might be possible:

   o  Prohibit use of the "exp" claim, as is done to prevent ID Token
      confusion.

   o  Where possible, use a separate "aud" claim value to distinguish
      between the SET subscriber and the protected resource that is the
      audience of an access token.

   o  Modify access token validation systems to check for the presence
      of the "events" claim as a means to detect security event tokens.
      This is particularly useful if the same endpoint may receive both
      types of tokens.

   o  Employ explicit typing, as described in Section 2.2, and modify
      access token validation systems to use the "typ" header parameter
      value.

4.7.  Distinguishing SETs from other kinds of JWTs

   JWTs are now being used in application areas beyond the identity
   applications in which they first appeared.  For instance, the Session
   Initiation Protocol (SIP) Via Header Field [RFC8055] and Personal
   Assertion Token (PASSporT) [I-D.ietf-stir-passport] specifications
   both define JWT profiles that use mostly or completely different sets
   of claims than are used by ID Tokens.  If it would otherwise be
   possible for an attacker to substitute a SET for one of these (or
   other) kinds of JWTs, then the SET profile must be defined in such a
   way that any substituted SET will result in its rejection when
   validated as the intended kind of JWT.

   The most direct way to ensure that a SET is not confused with another
   kind of JWT is to have the JWT validation logic reject JWTs
   containing an "events" claim unless the JWT is intended to be a SET.
   This approach can be employed for new systems but may not be
   applicable to existing systems.

   Another direct way to prevent confusion is to employ explicit typing,
   as described in Section 2.2, and modify applicable token validation

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   systems to use the "typ" header parameter value.  This approach can
   be employed for new systems but may not be applicable to existing
   systems.

   For many use cases, the simplest way to prevent substitution is
   requiring that the SET not include claims that are required for the
   kind of JWT that might be the target of an attack.  For example, for
   [RFC8055], the "sip_callid" claim could be omitted and for
   [I-D.ietf-stir-passport], the "orig" claim could be omitted.

   In many contexts, simple measures such as these will accomplish the
   task, should confusion otherwise even be possible.  Note that this
   topic is being explored in a more general fashion in JSON Web Token
   Best Current Practices [I-D.sheffer-oauth-jwt-bcp].  The proposed
   best practices in that draft may also be applicable for particular
   SET profiles and use cases.

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 feeds 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

6.1.  JSON Web Token Claims Registration

   This specification registers the "events" and "txn" claims in the
   IANA "JSON Web Token Claims" registry [IANA.JWT.Claims] established
   by [RFC7519].

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6.1.1.  Registry Contents

   o  Claim Name: "events"
   o  Claim Description: Security Event Object
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [[ this specification ]]

   o  Claim Name: "txn"
   o  Claim Description: Transaction Identifier
   o  Change Controller: IESG
   o  Specification Document(s): Section 2 of [[ this specification ]]

6.2.  Media Type Registration

6.2.1.  Registry Contents

   This section registers the "application/secevent+jwt" media type
   [RFC2046] in the "Media Types" registry [IANA.MediaTypes] in the
   manner described in [RFC6838], which can be used to indicate that the
   content is a SET.

   o  Type name: application
   o  Subtype name: secevent+jwt
   o  Required parameters: n/a
   o  Optional parameters: n/a
   o  Encoding considerations: 8bit; A SET is a JWT; JWT values are
      encoded as a series of base64url-encoded values (some of which may
      be the empty string) separated by period ('.') characters.
   o  Security considerations: See the Security Considerations section
      of [[ this specification ]]
   o  Interoperability considerations: n/a
   o  Published specification: Section 2.2 of [[ this specification ]]
   o  Applications that use this media type: TBD
   o  Fragment identifier considerations: n/a
   o  Additional information:

         Magic number(s): n/a
         File extension(s): n/a
         Macintosh file type code(s): n/a

   o  Person & email address to contact for further information:
      Michael B. Jones, mbj@microsoft.com
   o  Intended usage: COMMON
   o  Restrictions on usage: none
   o  Author: Michael B. Jones, mbj@microsoft.com
   o  Change controller: IESG
   o  Provisional registration?  No

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7.  References

7.1.  Normative References

   [IANA.JWT.Claims]
              IANA, "JSON Web Token Claims",
              <http://www.iana.org/assignments/jwt>.

   [IANA.MediaTypes]
              IANA, "Media Types",
              <http://www.iana.org/assignments/media-types>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <http://www.rfc-editor.org/info/rfc3986>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <http://www.rfc-editor.org/info/rfc6125>.

   [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
              RFC 6749, DOI 10.17487/RFC6749, October 2012,
              <http://www.rfc-editor.org/info/rfc6749>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <http://www.rfc-editor.org/info/rfc7525>.

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   [RFC7617]  Reschke, J., "The 'Basic' HTTP Authentication Scheme",
              RFC 7617, DOI 10.17487/RFC7617, September 2015,
              <http://www.rfc-editor.org/info/rfc7617>.

7.2.  Informative References

   [I-D.ietf-stir-passport]
              Wendt, C. and J. Peterson, "Personal Assertion Token
              (PASSporT)", draft-ietf-stir-passport-11 (work in
              progress), February 2017.

   [I-D.sheffer-oauth-jwt-bcp]
              Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", draft-sheffer-oauth-jwt-bcp-00 (work
              in progress), June 2017.

   [OpenID.Core]
              Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
              C. Mortimore, "OpenID Connect Core 1.0", November 2014,
              <http://openid.net/specs/openid-connect-core-1_0.html>.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              DOI 10.17487/RFC2046, November 1996,
              <http://www.rfc-editor.org/info/rfc2046>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <http://www.rfc-editor.org/info/rfc6838>.

   [RFC7009]  Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
              2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
              August 2013, <http://www.rfc-editor.org/info/rfc7009>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

   [RFC7516]  Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
              RFC 7516, DOI 10.17487/RFC7516, May 2015,
              <http://www.rfc-editor.org/info/rfc7516>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <http://www.rfc-editor.org/info/rfc7517>.

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   [RFC7644]  Hunt, P., Ed., Grizzle, K., Ansari, M., Wahlstroem, E.,
              and C. Mortimore, "System for Cross-domain Identity
              Management: Protocol", RFC 7644, DOI 10.17487/RFC7644,
              September 2015, <http://www.rfc-editor.org/info/rfc7644>.

   [RFC8055]  Holmberg, C. and Y. Jiang, "Session Initiation Protocol
              (SIP) Via Header Field Parameter to Indicate Received
              Realm", RFC 8055, DOI 10.17487/RFC8055, January 2017,
              <http://www.rfc-editor.org/info/rfc8055>.

   [saml-core-2.0]
              Internet2, "Assertions and Protocols for the OASIS
              Security Assertion Markup Language (SAML) V2.0", March
              2005.

Appendix A.  Acknowledgments

   The editors would like to thank the members of the IETF SCIM working
   group, which began discussions of provisioning events starting with
   draft-hunt-scim-notify-00 in 2015.

   The editors would like to thank the participants in the IETF id-event
   mailing list and related working groups for their support of this
   specification.

Appendix B.  Change Log

   From the original draft-hunt-idevent-token:

   Draft 01 - PH - Renamed eventUris to events

   Draft 00 - PH - First Draft

   Draft 01 - PH - Fixed some alignment issues with JWT.  Remove event
   type attribute.

   Draft 02 - PH - Renamed to Security Events, removed questions,
   clarified examples and intro text, and added security and privacy
   section.

   Draft 03 - PH

      General edit corrections from Sarah Squire

      Changed "event" term to "SET"

      Corrected author organization for William Denniss to Google

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      Changed definition of SET to be 2 parts, an envelope and 1 or more
      payloads.

      Clarified that the intent is to express a single event with
      optional extensions only.

   - mbj - Registered "events" claim, and proof-reading corrections.

   Draft 04 - PH -

   o  Re-added the "sub" claim with clarifications that any SET type may
      use it.

   o  Added additional clarification on the use of envelope vs. payload
      attributes

   o  Added security consideration for event timing.

   o  Switched use of "attribute" to "claim" for consistency.

   o  Revised examples to put "sub" claim back in the top level.

   o  Added clarification that SETs typically do not use "exp".

   o  Added security consideration for distinguishing Access Tokens and
      SETs.

   Draft 05 - PH - Fixed find/replace error that resulted in claim being
   spelled claimc

   Draft 06 - PH -

   o  Corrected typos

   o  New txn claim

   o  New security considerations Sequencing and Timing Issues

   Draft 07 -

   o  PH - Moved payload objects to be values of event URI attributes,
      per discussion.

   o  mbj - Applied terminology consistency and grammar cleanups.

   Draft 08 - PH -

   o  Added clarification to status of examples

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   o  Changed from primary vs. extension to state that multiple events
      may be expressed, some of which may or may not be considered
      extensions of others (which is for the subscriber or profiling
      specifications to determine).

   o  Other editorial changes suggested by Yaron
   From draft-ietf-secevent-token:

   Draft 00 - PH - First WG Draft based on draft-hunt-idevent-token

   Draft 01 - PH - Changes as follows:

   o  Changed terminology away from pub-sub to transmitter/receiver
      based on WG feedback

   o  Cleaned up/removed some text about extensions (now only used as
      example)

   o  Clarify purpose of spec vs. future profiling specs that define
      actual events

   Draft 02 - Changes are as follows:

   o  mbj - Added the Requirements for SET Profiles section.

   o  mbj - Expanded the Security Considerations section to describe how
      to prevent confusion of SETs with ID Tokens, access tokens, and
      other kinds of JWTs.

   o  mbj - Registered the "application/secevent+jwt" media type and
      defined how to use it for explicit typing of SETs.

   o  mbj - Clarified the misleading statement that used to say that a
      SET conveys a single security event.

   o  mbj - Added a note explicitly acknowledging that some SET profiles
      may choose to convey event subject information in the event
      payload.

   o  PH - Corrected encoded claim example on page 10.

   o  mbj - Applied grammar corrections.

Authors' Addresses

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   Phil Hunt (editor)
   Oracle Corporation

   Email: phil.hunt@yahoo.com

   William Denniss
   Google

   Email: wdenniss@google.com

   Morteza Ansari
   Cisco

   Email: morteza.ansari@cisco.com

   Michael B. Jones
   Microsoft

   Email: mbj@microsoft.com
   URI:   http://self-issued.info/

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