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rfc:rfc8417

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.

Hunt, et al. Standards Track [Page 1] RFC 8417 SET July 2018

Copyright Notice

 Copyright (c) 2018 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Hunt, et al. Standards Track [Page 2] RFC 8417 SET July 2018

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

Hunt, et al. Standards Track [Page 3] RFC 8417 SET July 2018

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

Hunt, et al. Standards Track [Page 4] RFC 8417 SET July 2018

 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.

Hunt, et al. Standards Track [Page 5] RFC 8417 SET July 2018

 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

Hunt, et al. Standards Track [Page 6] RFC 8417 SET July 2018

    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.

Hunt, et al. Standards Track [Page 7] RFC 8417 SET July 2018

 {
   "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.

Hunt, et al. Standards Track [Page 8] RFC 8417 SET July 2018

 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.

Hunt, et al. Standards Track [Page 9] RFC 8417 SET July 2018

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.

Hunt, et al. Standards Track [Page 10] RFC 8417 SET July 2018

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.

Hunt, et al. Standards Track [Page 11] RFC 8417 SET July 2018

 "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.)

Hunt, et al. Standards Track [Page 12] RFC 8417 SET July 2018

 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".

Hunt, et al. Standards Track [Page 13] RFC 8417 SET July 2018

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

Hunt, et al. Standards Track [Page 14] RFC 8417 SET July 2018

 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].

Hunt, et al. Standards Track [Page 15] RFC 8417 SET July 2018

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.

Hunt, et al. Standards Track [Page 16] RFC 8417 SET July 2018

    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.

Hunt, et al. Standards Track [Page 17] RFC 8417 SET July 2018

 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.

Hunt, et al. Standards Track [Page 18] RFC 8417 SET July 2018

 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.

Hunt, et al. Standards Track [Page 19] RFC 8417 SET July 2018

 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

Hunt, et al. Standards Track [Page 20] RFC 8417 SET July 2018

 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.

Hunt, et al. Standards Track [Page 21] RFC 8417 SET July 2018

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.

Hunt, et al. Standards Track [Page 22] RFC 8417 SET July 2018

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.

Hunt, et al. Standards Track [Page 23] RFC 8417 SET July 2018

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

Hunt, et al. Standards Track [Page 24] RFC 8417 SET July 2018

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>.

Hunt, et al. Standards Track [Page 25] RFC 8417 SET July 2018

 [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>.

Hunt, et al. Standards Track [Page 26] RFC 8417 SET July 2018

 [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.

Hunt, et al. Standards Track [Page 27] RFC 8417 SET July 2018

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

Hunt, et al. Standards Track [Page 28]

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