Security Event Token (SET)

Internet Engineering Task Force (IETF)                      P. Hunt, Ed.
Request for Comments: 8417                                        Oracle
Category: Standards Track                                       M. Jones
ISSN: 2070-1721                                                Microsoft
                                                              W. Denniss
                                                                  Google
                                                               M. Ansari
                                                                   Cisco
                                                               July 2018


                       Security Event Token (SET)

Abstract

   This specification defines the Security Event Token (SET) data
   structure.  A SET describes statements of fact from the perspective
   of an issuer about a subject.  These statements of fact represent an
   event that occurred directly to or about a security subject, for
   example, a statement about the issuance or revocation of a token on
   behalf of a subject.  This specification is intended to enable
   representing security- and identity-related events.  A SET is a JSON
   Web Token (JWT), which can be optionally signed and/or encrypted.
   SETs can be distributed via protocols such as HTTP.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8417.

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 . . . . . . . . . . . . . . . . . .   4
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   5
     1.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  The Security Event Token (SET)  . . . . . . . . . . . . . . .   6
     2.1.  Illustrative Examples . . . . . . . . . . . . . . . . . .   7
       2.1.1.  SCIM Example  . . . . . . . . . . . . . . . . . . . .   7
       2.1.2.  Logout Example  . . . . . . . . . . . . . . . . . . .   9
       2.1.3.  Consent Example . . . . . . . . . . . . . . . . . . .  10
       2.1.4.  RISC Example  . . . . . . . . . . . . . . . . . . . .  11
     2.2.  Core SET Claims . . . . . . . . . . . . . . . . . . . . .  11
     2.3.  Explicit Typing of SETs . . . . . . . . . . . . . . . . .  13
     2.4.  Security Event Token Construction . . . . . . . . . . . .  14
   3.  Requirements for SET Profiles . . . . . . . . . . . . . . . .  16
   4.  Preventing Confusion between SETs and Other JWTs  . . . . . .  17
     4.1.  Distinguishing SETs from ID Tokens  . . . . . . . . . . .  17
     4.2.  Distinguishing SETs from Access Tokens  . . . . . . . . .  18
     4.3.  Distinguishing SETs from Other Kinds of JWTs  . . . . . .  18
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
     5.1.  Confidentiality and Integrity . . . . . . . . . . . . . .  19
     5.2.  Delivery  . . . . . . . . . . . . . . . . . . . . . . . .  20
     5.3.  Sequencing  . . . . . . . . . . . . . . . . . . . . . . .  20
     5.4.  Timing Issues . . . . . . . . . . . . . . . . . . . . . .  20
     5.5.  Preventing Confusion  . . . . . . . . . . . . . . . . . .  21
   6.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  21
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
     7.1.  JSON Web Token Claims Registration  . . . . . . . . . . .  22
       7.1.1.  Registry Contents . . . . . . . . . . . . . . . . . .  22
     7.2.  Structured Syntax Suffix Registration . . . . . . . . . .  22
       7.2.1.  Registry Contents . . . . . . . . . . . . . . . . . .  23
     7.3.  Media Type Registration . . . . . . . . . . . . . . . . .  24
       7.3.1.  Registry Contents . . . . . . . . . . . . . . . . . .  24
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  25
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  26
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Introduction and Overview

   This specification defines an extensible Security Event Token (SET)
   data structure, which can 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].

   This specification profiles the use of JWT for the purpose of issuing
   SETs.  This specification defines a base format used by profiling
   specifications to define actual events and their meanings.  This
   specification uses non-normative example events to demonstrate how
   events can be constructed.

   This specification is scoped to security- and identity-related
   events.  While SETs 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 SET
   describes statements of fact from the perspective of an issuer about
   a subject (e.g., a web resource, token, IP address, the issuer
   itself).  These statements of fact represent a logical event that
   occurred directly to or about a security subject, for example, a
   statement about the issuance or revocation of a token on behalf of a
   subject.  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.

   o  An indication that a user has been given control of an email
      identifier that was previously controlled by another user.

   While subject state changes are often triggered by a user agent or
   security subsystem, the issuance and transmission of an event may
   occur asynchronously and in a back channel to the action that caused
   the change that generated the security event.  Subsequently, a SET
   recipient, 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 SET recipient may choose to
   ensure that the new user is not granted access to resources
   associated with the previous user.  Or, the SET recipient may not
   have any relationship with the subject, and no action is taken.

   While SET recipients will often take actions upon receiving SETs,
   security events cannot be assumed to be commands or requests.  The
   intent of this specification is to define a syntax for statements of
   fact that SET recipients may interpret for their own purposes.

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
   [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] conforming to this specification.

   SET Issuer
      A service provider that creates SETs to be sent to other service
      providers known as SET recipients.

   SET Recipient
      A SET recipient is an entity that receives SETs through some
      distribution method.  A SET recipient is the same entity referred
      as a "recipient" in [RFC7519] or "receiver" in related
      specifications.

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

   Event Identifier
      A member name for an element of the JSON object that is the value
      of the "events" claim in a SET.  This member name MUST be a URI.

   Event Payload
      A member value for an element of the JSON object that is the value
      of the "events" claim in a SET.  This member value MUST be a JSON
      object.

   Profiling Specification
      A specification that profiles the SET data structure to define one
      or more specific event types and their associated claims and
      processing rules.

2.  The Security Event Token (SET)

   A SET is a JWT [RFC7519] data structure that represents one or more
   related aspects of a security event that occurred to a subject.  The
   JWT Claims Set in a SET has the following structure:

   o  The top-level claims in the JWT Claims Set are called the SET
      "envelope".  Some of these claims are present in every SET; others
      will be specific to particular SET profiles or profile families.
      Claims in the envelope SHOULD be registered in the "JSON Web Token
      Claims" registry [IANA.JWT.Claims] or be Public Claims or Private
      Claims, as defined in [RFC7519].

   o  Envelope claims that are profiled and defined in this
      specification are used to validate the SET and provide information
      about the event data included in the SET.  The "events" claim
      contains the event identifiers and event-specific data expressed
      about the security subject.  The envelope MAY include event-
      specific or profile-specific data.  The "events" claim value MUST
      be a JSON object that contains at least one member.

   o  Each member of the "events" JSON object is a name/value pair.  The
      JSON member name is a URI string value, which is the event
      identifier, and the corresponding value is a JSON object known as
      the event "payload".  The payload JSON object contains claims that
      pertain to that event identifier and need not be registered as JWT
      claims.  These claims are defined by the profiling specification
      that defines the event.  An event with no payload claims SHALL be
      represented as the empty JSON object ("{}").

   o  When multiple event identifiers are contained in a SET, they
      represent multiple aspects of the same state transition that
      occurred to the security subject.  They are not intended to be
      used to aggregate distinct events about the same subject.  Beyond
      this, the interpretation of SETs containing multiple event
      identifiers is out of scope for this specification; profiling
      specifications MAY define their own rules regarding their use of
      SETs containing multiple event identifiers, as described in
      Section 3.  Possible uses of multiple values include, but are not
      limited to:

      *  Values to provide classification information (e.g., threat type
         or level).

      *  Additions to existing event representations.

      *  Values used to link potential series of events.

      *  Specific-purpose event URIs used between particular SET issuers
         and SET recipients.

2.1.  Illustrative Examples

   This section illustrates several possible uses of SETs through non-
   normative examples.

2.1.1.  SCIM Example

   The following example shows the JWT Claims Set for a hypothetical
   System for Cross-domain Identity Management (SCIM) [RFC7644] password
   reset SET.  Such a SET might be used by a receiver as a trigger to
   reset active user-agent sessions related to the identified user.

   {
     "iss": "https://scim.example.com",
     "iat": 1458496025,
     "jti": "3d0c3cf797584bd193bd0fb1bd4e7d30",
     "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 JWT Claims Set usage consists of:

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

   o  The "iss" claim, denoting the SET issuer.

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

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

   The SET contains two event payloads:

   o  The "id" claim represents SCIM's unique identifier for a subject.

   o  The second payload identified by "https://example.com/scim/event/
      passwordResetExt" and the payload claim "resetAttempts" conveys
      the current count of reset attempts.  In this example, while the
      count is a simple factual statement for the issuer, the meaning of
      the value (a count) is up to the receiver.  As an example, such a
      value might be used by the receiver to infer increasing risk.

   In this example, the SCIM event indicates that a password has been
   updated and the current password reset count is 5.  Notice that the
   value for "resetAttempts" is in the event payload of an event used to
   convey this information.

2.1.2.  Logout Example

   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
   claims "sub" and "sid" to identify the subject that was logged out.
   At the time of this writing, this example corresponds to the logout
   token defined in the OpenID Connect Back-Channel Logout 1.0
   [OpenID.BackChannel] specification.

2.1.3.  Consent Example

   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:

   {
     "iss": "https://my.med.example.org",
     "iat": 1458496025,
     "jti": "fb4e75b5411e4e19b6c0fe87950f7749",
     "aud": [
       "https://rp.example.com"
     ],
     "events": {
       "https://openid.net/heart/specs/consent.html": {
         "iss": "https://connect.example.com",
         "sub": "248289761001",
         "consentUri": [
           "https://terms.med.example.org/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
   SET issuer "https://my.med.example.org".  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.

2.1.4.  RISC Example

   The following example JWT Claims Set is for an account disabled
   event.  At the time of this writing, this example corresponds to the
   account disabled event defined in the OpenID RISC Event Types 1.0
   [OpenID.RISC.Events] specification.

  {
    "iss": "https://idp.example.com/",
    "jti": "756E69717565206964656E746966696572",
    "iat": 1508184845,
    "aud": "636C69656E745F6964",
    "events": {
  "https://schemas.openid.net/secevent/risc/event-type/account-disabled"
          : {
        "subject": {
          "subject_type": "iss-sub",
          "iss": "https://idp.example.com/",
          "sub": "7375626A656374"
        },
        "reason": "hijacking"
      }
    }
  }

                       Figure 4: Example RISC Event

   Notice that parameters to the event are included in the event
   payload, in this case, the "reason" and "cause-time" values.  The
   subject of the event is identified using the "subject" payload value,
   which itself is a JSON object.

2.2.  Core SET Claims

   The following claims from [RFC7519] are profiled for use in SETs:

   "iss" (Issuer) Claim
      As defined by Section 4.1.1 of [RFC7519], this claim contains a
      string identifying the service provider publishing the SET (the
      issuer).  In some cases, the issuer of the SET will not be the
      issuer associated with the security subject of the SET.
      Therefore, implementers cannot assume that the issuers are the
      same unless the profiling specification specifies that they are
      for SETs conforming to that profile.  This claim is REQUIRED.

   "iat" (Issued At) Claim
      As defined by Section 4.1.6 of [RFC7519], this claim contains a
      value representing when the SET was issued.  This claim is
      REQUIRED.

   "jti" (JWT ID) Claim
      As defined by Section 4.1.7 of [RFC7519], this claim contains a
      unique identifier for the SET.  The identifier MUST be unique
      within a particular event feed and MAY be used by clients to track
      whether a particular SET has already been received.  This claim is
      REQUIRED.

   "aud" (Audience) Claim
      As defined by Section 4.1.3 of [RFC7519], this claim contains one
      or more audience identifiers for the SET.  This claim is
      RECOMMENDED.

   "sub" (Subject) Claim
      As defined by Section 4.1.2 of [RFC7519], this claim contains a
      StringOrURI value representing the principal that is the subject
      of the SET.  This is usually the entity whose "state" was changed.
      For example:

      *  an IP Address was added to a blacklist;

      *  a URI representing a user resource that was modified; or,

      *  a token identifier (e.g. "jti") for a revoked token.

      If used, the profiling specification MUST 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
      (either using the "sub" member name or another name), 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" (Expiration Time) Claim
      As defined by Section 4.1.4 of [RFC7519], this claim is the time
      after which the JWT MUST NOT be accepted for processing.  In the
      context of a SET, however, this notion does not typically apply,
      since a SET represents something that has already occurred and is
      historical in nature.  Therefore, its use is NOT RECOMMENDED.
      (Also, see Section 4.1 for additional reasons not to use the "exp"
      claim in some SET use cases.)

   The following new claims are defined by this specification:

   "events" (Security Events) Claim
      This claim contains a set of event statements that each provide
      information describing a single logical event that has occurred
      about a security subject (e.g., a state change to the subject).
      Multiple event identifiers with the same value MUST NOT be used.
      The "events" claim MUST NOT be used to express multiple
      independent logical events.

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

   "txn" (Transaction Identifier) Claim
      An OPTIONAL string value that represents a unique transaction
      identifier.  In cases in which multiple related JWTs are issued,
      the transaction identifier claim can be used to correlate these
      related JWTs.  Note that this claim can be used in JWTs that are
      SETs and also in JWTs using non-SET profiles.

   "toe" (Time of Event) Claim
      A value that represents the date and time at which the event
      occurred.  This value is a NumericDate (see Section 2 of
      [RFC7519]).  By omitting this claim, the issuer indicates that
      they are not sharing an event time with the recipient.  (Note that
      in some use cases, the represented time might be approximate;
      statements about the accuracy of this field MAY be made by
      profiling specifications.)  This claim is OPTIONAL.

2.3.  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".

2.4.  Security Event Token Construction

   This section describes how to construct a SET.

   The following is an example JWT Claims Set for a hypothetical SCIM
   SET:

   {
     "iss": "https://scim.example.com",
     "iat": 1458496404,
     "jti": "4d3559ec67504aaba65d40b0363faad8",
     "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 5: Example Event Claims

   The JSON Claims Set is encoded per [RFC7519].

   In this example, the SCIM SET claims are encoded in an unsecured JWT.
   The JOSE Header for this example is:

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

   Base64url encoding (as defined by Section 2 of [RFC7515], including
   the omission of all trailing '=' characters) of the octets of the
   UTF-8 [RFC3629] representation of the JOSE Header yields:

     eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJub25lIn0
   The above example JWT Claims Set (with insignificant whitespace
   removed) is encoded as follows (with line breaks for display purposes
   only):

     eyJpc3MiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20iLCJpYXQiOjE0NTg0OTY0M
     DQsImp0aSI6IjRkMzU1OWVjNjc1MDRhYWJhNjVkNDBiMDM2M2ZhYWQ4IiwiYXVkIj
     pbImh0dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg
     3OTU5M2I3NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYw
     NDUxNmIxZDA4NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybjppZXRmOnBhcmFtc
     zpzY2ltOmV2ZW50OmNyZWF0ZSI6eyJyZWYiOiJodHRwczovL3NjaW0uZXhhbXBsZS
     5jb20vVXNlcnMvNDRmNjE0MmRmOTZiZDZhYjYxZTc1MjFkOSIsImF0dHJpYnV0ZXM
     iOlsiaWQiLCJuYW1lIiwidXNlck5hbWUiLCJwYXNzd29yZCIsImVtYWlscyJdfX19

   The encoded JWS signature is the empty string.

   Concatenating the three encoded parts (JOSE Header, JWT Claims Set,
   and JWS signature) in order with period ('.') characters between the
   parts yields this complete SET (with line breaks for display purposes
   only):

     eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJub25lIn0
     .
     eyJpc3MiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20iLCJpYXQiOjE0NTg0OTY0M
     DQsImp0aSI6IjRkMzU1OWVjNjc1MDRhYWJhNjVkNDBiMDM2M2ZhYWQ4IiwiYXVkIj
     pbImh0dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg
     3OTU5M2I3NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYw
     NDUxNmIxZDA4NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybjppZXRmOnBhcmFtc
     zpzY2ltOmV2ZW50OmNyZWF0ZSI6eyJyZWYiOiJodHRwczovL3NjaW0uZXhhbXBsZS
     5jb20vVXNlcnMvNDRmNjE0MmRmOTZiZDZhYjYxZTc1MjFkOSIsImF0dHJpYnV0ZXM
     iOlsiaWQiLCJuYW1lIiwidXNlck5hbWUiLCJwYXNzd29yZCIsImVtYWlscyJdfX19
     .

             Figure 6: Example Unsecured Security Event Token

   For the purpose of having a simpler example in Figure 6, an unsecured
   token is shown.  When SETs are not signed or encrypted, other
   mechanisms such as TLS MUST be employed to provide integrity
   protection, confidentiality, and issuer authenticity, 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

   Profiling specifications of this specification define actual SETs to
   be used in particular use cases.  These profiling specifications
   define the syntax and semantics of SETs conforming to that SET
   profile and rules for validating those SETs.  Profiling
   specifications SHOULD define syntax, semantics, subject
   identification, and validation.

   Syntax
      The syntax of the SETs defined, including:

      Top-Level Claims
         Claims and values in the JWT Claims Set.  Examples are claims
         defined by the JWT specification [RFC7519], this specification,
         and by the profiling specification.

      Event Payload
         The JSON data structure contents and format, containing event-
         specific information, if any (see Section 1.2).

   Semantics
      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.
      Likewise, if the profile allows (or requires) that the JWT be
      unsecured, the means by which the integrity of the JWT is ensured
      MUST be specified.

   Subject Identification
      Profiling specifications MUST define how the event subject is
      identified in the SET, as well as how to differentiate between the
      event subject's issuer and the SET issuer, if applicable.  It is
      NOT RECOMMENDED for profiling specifications to use the "sub"
      claim in cases in which the subject is not globally unique and has
      a different issuer from the SET itself.

   Validation
      Profiling 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.

      Among the syntax and semantics of SETs that a profiling
      specification may define is whether the value of the "events"
      claim may contain multiple members, and what processing
      instructions are employed in the single- and multiple-valued cases
      for SETs conforming to that profile.  Many valid choices are
      possible.  For instance, some profiles might allow multiple event
      identifiers to be present and specify that any that are not
      understood by recipients be ignored, thus enabling extensibility.
      Other profiles might allow multiple event identifiers to be
      present but require that all be understood if the SET is to be
      accepted.  Some profiles might require that only a single value be
      present.  All such choices are within the scope of profiling
      specifications to define.

4.  Preventing Confusion between SETs and Other JWTs

   Because [RFC7519] states that "all claims that are not understood by
   implementations MUST be ignored", there is a consideration that a SET
   might be confused with another kind of JWT from the same issuer.
   Unless this confusion is prevented, this might enable an attacker who
   possesses a SET to use it in a context in which another kind of JWT
   is expected, or vice versa.  This section presents concrete
   techniques for preventing confusion between SETs and several other
   specific kinds of JWTs, as well as generic techniques for preventing
   possible confusion between SETs and other kinds of JWTs.

4.1.  Distinguishing SETs from ID Tokens

   A SET might be confused with an ID Token [OpenID.Core] if a SET is
   mistakenly or maliciously 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 contexts for which substitution is
   possible.

   Note that the use of explicit typing, as described in Section 2.3,
   will not achieve disambiguation between ID Tokens and SETs, as the ID
   Token validation rules do not use the "typ" header parameter value.

4.2.  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, also implementation specific, generally.  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 recipient 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 2.3, and modify
      access token validation systems to use the "typ" header parameter
      value.

4.3.  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 Parameter to
   Indicate Received Realm" [RFC8055] and "PASSporT: Personal Assertion
   Token" [RFC8225] 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 prevent confusion is to employ explicit
   typing, as described in Section 2.3, and modify applicable token
   validation systems to use the "typ" header parameter value.  This
   approach can be employed for new systems but may not be applicable to
   existing systems.

   Another 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.  Validating that the JWT has an "events" claim will be
   effective in preventing attackers from passing other kinds of JWTs
   off as SETs.

   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 [RFC8225],
   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" [JWT-BCP].  The proposed best practices in
   that document may also be applicable for particular SET profiles and
   use cases.

5.  Security Considerations

5.1.  Confidentiality and Integrity

   SETs may 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] or a higher version and MAY support additional
   transport-layer mechanisms meeting its security requirements.  When
   using TLS, the client MUST perform a TLS server certificate check,
   per [RFC6125].  Implementation security considerations for TLS can be
   found in "Recommendations for Secure Use of Transport Layer Security
   (TLS) and Datagram Transport Layer Security (DTLS)" [RFC7525].

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

   Unless integrity of the JWT is ensured by other means, it MUST be
   signed using JWS [RFC7515] by an issuer that is trusted to do so for
   the use case so that the SET can be authenticated and validated by
   the SET recipient.

5.2.  Delivery

   This specification does not define a delivery mechanism for SETs.  In
   addition to confidentiality and integrity (discussed above),
   implementers and profiling 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 (mutual) TLS, there is no assurance that
   the correct endpoint received the SET and that it could be
   successfully processed.

5.3.  Sequencing

   This specification defines no means of ordering multiple SETs in a
   sequence.  Depending on the type and nature of the events represented
   by SETs, order may or may not matter.  For example, in provisioning,
   event order is critical -- an object cannot be modified before it is
   created.  In other SET types, such as a token revocation, the order
   of SETs for revoked tokens does not matter.  If, however, the event
   conveys a logged 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
   will have some amount of clock skew.  Thus, time by itself will not
   guarantee order.

   Specifications profiling SET SHOULD define a mechanism for detecting
   order or sequence of events when the order matters.  For example, the
   "txn" claim could contain an ordered value (e.g., a counter) that the
   issuer includes, although just as for timestamps, ensuring such
   ordering can be difficult in distributed systems.

5.4.  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 SET
   recipient in advance of or behind the process that caused the event.
   For example, a user having been required to log out and then log back
   in again, may cause a "token revoked" SET to be issued, typically
   causing the receiver to reset all active sessions at the receiver
   that are related to that user.  If a revocation SET arrives at the
   same time as the user agent re-logs in, timing could cause problems
   by erroneously treating the new user session as logged out.
   Profiling specifications SHOULD be careful to consider both SET
   expression and timing issues.  For example, it might be more
   appropriate to revoke a specific session or ID Token rather than a
   general logout statement about a "user".  Alternatively, profiling
   specifications could use timestamps that allow new sessions to be
   started immediately after a stated logout event time.

5.5.  Preventing Confusion

   Also, see Section 4 above for both additional security considerations
   and normative text on preventing SETs from being confused with other
   kinds of JWTs.

6.  Privacy Considerations

   If a SET needs to be retained for audit purposes, the signature can
   be used to provide verification of its authenticity.

   SET issuers SHOULD attempt to specialize SETs so that their content
   is targeted to the specific business and protocol needs of the
   intended SET recipients.

   When sharing personally identifiable information or information that
   is otherwise considered confidential to affected users, SET issuers
   and recipients should have the appropriate legal agreements and user
   consent and/or terms of service in place.

   The propagation of subject identifiers can be perceived as personally
   identifiable information.  Where possible, SET issuers and recipients
   SHOULD devise approaches that prevent propagation -- for example, the
   passing of a salted hash value that requires the SET recipient to
   know the subject.

   In some cases, it may be possible for a SET recipient to correlate
   different events and thereby gain information about a subject that
   the SET issuer did not intend to share.  For example, a SET recipient
   might be able to use "iat" values or highly precise "toe" values to
   determine that two otherwise un-relatable events actually relate to
   the same real-world event.  The union of information from both events
   could allow a SET recipient to de-anonymize data or recognize that
   unrelated identifiers relate to the same individual.  SET issuers
   SHOULD take steps to minimize the chance of event correlation, when
   such correlation would constitute a privacy violation.  For instance,
   they could use approximate values for the "toe" claim or arbitrarily
   delay SET issuance, where such delay can be tolerated.

7.  IANA Considerations

7.1.  JSON Web Token Claims Registration

   IANA has registered the "events", "toe", and "txn" claims in the IANA
   "JSON Web Token Claims" registry [IANA.JWT.Claims] established by
   [RFC7519].

7.1.1.  Registry Contents

   o  Claim Name: "events"
   o  Claim Description: Security Events
   o  Change Controller: IESG
   o  Specification Document(s): Section 2.2 of [RFC8417]

   o  Claim Name: "toe"
   o  Claim Description: Time of Event
   o  Change Controller: IESG
   o  Specification Document(s): Section 2.2 of [RFC8417]

   o  Claim Name: "txn"
   o  Claim Description: Transaction Identifier
   o  Change Controller: IESG
   o  Specification Document(s): Section 2.2 of [RFC8417]

7.2.  Structured Syntax Suffix Registration

   IANA has registered the "+jwt" structured syntax suffix [RFC6838] in
   the "Structured Syntax Suffix" registry [IANA.StructuredSuffix] in
   the manner described in [RFC6838], which can be used to indicate that
   the media type is encoded as a JWT.

7.2.1.  Registry Contents

   o  Name: JSON Web Token (JWT)
   o  +suffix: +jwt
   o  References: Section 3 of [RFC7519], Section 7.2 of [RFC8417]
   o  Encoding Considerations: binary; JWT values are encoded as a
      series of base64url-encoded values (with trailing '=' characters
      removed), some of which may be the empty string, separated by
      period ('.') characters.
   o  Interoperability Considerations: N/A
   o  Fragment Identifier Considerations:
      The syntax and semantics of fragment identifiers specified for
      +jwt SHOULD be as specified for "application/jwt".  (At
      publication of this document, there is no fragment identification
      syntax defined for "application/jwt".)

      The syntax and semantics for fragment identifiers for a specific
      "xxx/yyy+jwt" SHOULD be processed as follows:

      For cases defined in +jwt where the fragment identifier resolves
      per the +jwt rules, process as specified in +jwt.

      For cases defined in +jwt where the fragment identifier does not
      resolve per the +jwt rules, process as specified in "xxx/yyy+jwt".

      For cases not defined in +jwt, process as specified in "xxx/
      yyy+jwt".
   o  Security Considerations: See Section 11 of [RFC7519].
   o  Contact:
      Michael B. Jones, mbj@microsoft.com
   o  Author/Change Controller:
      Security Events Working Group.
      The IESG has change control over this registration.

7.3.  Media Type Registration

7.3.1.  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: binary; A SET is a JWT; JWT values are
      encoded as a series of base64url-encoded values (with trailing '='
      characters removed), some of which may be the empty string,
      separated by period ('.') characters.
   o  Security considerations: See Section 5 of [RFC8417]
   o  Interoperability considerations: N/A
   o  Published specification: Section 2.3 of [RFC8417]
   o  Applications that use this media type: Applications that exchange
      SETs
   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

8.  References

8.1.  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>.

   [IANA.StructuredSuffix]
              IANA, "Structured Syntax Suffix",
              <https://www.iana.org/assignments/
              media-type-structured-suffix/>.

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

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

   [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,
              <https://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,
              <https://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, <https://www.rfc-editor.org/info/rfc6125>.

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

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

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

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://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, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [JWT-BCP]  Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", Work in Progress,
              draft-ietf-oauth-jwt-bcp-03, May 2018.

   [OpenID.BackChannel]
              Jones, M. and J. Bradley, "OpenID Connect Back-Channel
              Logout 1.0", January 2017, <http://openid.net/specs/
              openid-connect-backchannel-1_0.html>.

   [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>.

   [OpenID.RISC.Events]
              Scurtescu, M., Backman, A., Hunt, P., and J. Bradley,
              "OpenID RISC Event Types 1.0", April 2018,
              <http://openid.net/specs/
              openid-risc-event-types-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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc6838>.

   [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, <https://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,
              <https://www.rfc-editor.org/info/rfc8055>.

   [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
              Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
              <https://www.rfc-editor.org/info/rfc8225>.

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, the Security
   Events working group, and related working groups for their
   contributions to this specification.  The specification incorporates
   suggestions made by many people, including Annabelle Backman, John
   Bradley, Alissa Cooper, Ned Freed, Dick Hardt, Russ Housley, Benjamin
   Kaduk, Mirja Kuehlewind, Mark Lizar, Alexey Melnikov, Andrew Nash,
   Eric Rescorla, Adam Roach, Justin Richer, Nat Sakimura, Marius
   Scurtescu, Yaron Sheffer, and Martin Vigoureux.

Authors' Addresses

   Phil Hunt (editor)
   Oracle Corporation

   Email: phil.hunt@yahoo.com


   Michael B. Jones
   Microsoft

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


   William Denniss
   Google

   Email: rfc8417@wdenniss.com
   URI:   https://wdenniss.com/SET


   Morteza Ansari
   Cisco

   Email: morteza.ansari@cisco.com