Internet Engineering Task Force (IETF) P. Hunt, Ed.

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):
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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
.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.

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, [email protected]
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, [email protected]
o Intended usage: COMMON
o Restrictions on usage: none
o Author: Michael B. Jones, [email protected]
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: [email protected]

Michael B. Jones
Microsoft

Email: [email protected]
URI: http://self-issued.info/

William Denniss
Google

Email: [email protected]
URI: https://wdenniss.com/SET

Morteza Ansari
Cisco

Email: [email protected]

Hunt, et al. Standards Track [Page 28]