| Security Events Working Group | P. Hunt, Ed. |
| Internet-Draft | Oracle |
| Intended status: Standards Track | W. Denniss |
| Expires: January 1, 2018 | |
| M. Ansari | |
| Cisco | |
| M. Jones | |
| Microsoft | |
| June 30, 2017 |
Security Event Token (SET)
draft-ietf-secevent-token-02
This specification defines the Security Event Token, which may be distributed via a protocol such as HTTP. The Security Event Token (SET) specification profiles the JSON Web Token (JWT), which can be optionally signed and/or encrypted. A SET describes a statement of fact from the perspective of an issuer that it intends to share with one or more receivers.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 1, 2018.
Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.
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This specification defines an extensible Security Event Token (SET) format which may be exchanged using protocols such as HTTP. The specification builds on the JSON Web Token (JWT) format [RFC7519] in order to provide a self-contained token that can be optionally signed using JSON Web Signature (JWS) [RFC7515] and/or encrypted using JSON Web Encryption (JWE) [RFC7516].
This specification profiles the use of JWT for the purpose of issuing security event tokens (SETs). This specification defines a base format upon which profiling specifications define actual events and their meanings. Unless otherwise specified, this specification uses non-normative example events intended to demonstrate how events may be constructed.
This specification is scoped to security and identity related events. While security event tokens may be used for other purposes, the specification only considers security and privacy concerns relevant to identity and personal information.
Security Events are not commands issued between parties. A security event is a statement of fact from the perspective of an issuer about the state of a security subject (e.g., a web resource, token, IP address, the issuer itself) that the issuer controls or is aware of, that has changed in some way (explicitly or implicitly). A security subject MAY be permanent (e.g., a user account) or temporary (e.g., an HTTP session) in nature. A state change could describe a direct change of entity state, an implicit change of state or other higher-level security statements such as:
While subject state changes are often triggered by a user-agent or security-subsystem, the issuance and transmission of an event often occurs asynchronously and in a back-channel to the action which caused the change that generated the security event. Subsequently, an Event Receiver, having received a SET, validates and interprets the received SET and takes its own independent actions, if any. For example, having been informed of a personal identifier being associated with a different security subject (e.g., an email address is being used by someone else), the Event Receiver may choose to ensure that the new user is not granted access to resources associated with the previous user. Or, the Event Receiver may not have any relationship with the subject, and no action is taken.
While Event Receivers will often take actions upon receiving SETs, security events MUST NOT be assumed to be commands or requests. The intent of this specification is to define a way of exchanging statements of fact that subscribers may interpret for their own purposes. As such, SETs have no capability for error signaling other to ensure the validation of a received SET.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. These keywords are capitalized when used to unambiguously specify requirements of the protocol or application features and behavior that affect the inter-operability and security of implementations. When these words are not capitalized, they are meant in their natural-language sense.
For purposes of readability, examples are not URL encoded. Implementers MUST percent encode URLs as described in Section 2.1 of.
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.
The following definitions are used with SETs:
A SET is a data structure (in the form of a JWT [RFC7519]) representing one or more related security events about a Subject.
The schema and structure of a SET follows the JWT [RFC7519] specification. A SET has the following structure:
The following is a non-normative example showing the JWT Claims Set for a hypothetical SCIM password reset SET. This example shows an additional events value (https://example.com/scim/event/passwordResetExt) used to convey additional information -- in this case, the current count of reset attempts:
{
"jti": "3d0c3cf797584bd193bd0fb1bd4e7d30",
"iat": 1458496025,
"iss": "https://scim.example.com",
"aud": [
"https://jhub.example.com/Feeds/98d52461fa5bbc879593b7754",
"https://jhub.example.com/Feeds/5d7604516b1d08641d7676ee7"
],
"sub": "https://scim.example.com/Users/44f6142df96bd6ab61e7521d9",
"events": {
"urn:ietf:params:scim:event:passwordReset":
{ "id":"44f6142df96bd6ab61e7521d9"},
"https://example.com/scim/event/passwordResetExt":
{ "resetAttempts":5}
}
}
Figure 1: Example SCIM Password Reset Event
The event in the figure above expresses hypothetical password reset event for SCIM [RFC7644]. The JWT consists of:
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 actually part of its own JSON object associated with its own event URI attribute.
Here is another example JWT Claims Set for a security event token, this one for a Logout Token:
{
"iss": "https://server.example.com",
"sub": "248289761001",
"aud": "s6BhdRkqt3",
"iat": 1471566154,
"jti": "bWJq",
"sid": "08a5019c-17e1-4977-8f42-65a12843ea02",
"events": {
"http://schemas.openid.net/event/backchannel-logout": {}
}
}
Figure 2: Example OpenID Back-Channel Logout Event
In the following example JWT Claims Set, a fictional medical service collects consent for medical actions and notifies other parties. The individual for whom consent is identified was originally authenticated via OpenID Connect. In this case, the issuer of the security event is an application rather than the OpenID provider:
{
"jti": "fb4e75b5411e4e19b6c0fe87950f7749",
"sub": "248289761001",
"iat": 1458496025,
"iss": "https://my.examplemed.com",
"aud": [
"https://rp.example.com"
],
"events": {
"https://openid.net/heart/specs/consent.html":{
"iss":"https://connect.example.com",
"consentUri":[
"https://terms.examplemed.com/labdisclosure.html#Agree"
]
}
}
}
Figure 3: Example Consent Event
The following are claims that are based on [RFC7519] claim definitions and are profiled for use in an event token:
The following are new claims defined by this specification:
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.
A SET is a JWT [RFC7519] that is constructed by building a JSON structure that constitutes an event object which is then used as the body of a JWT.
While this specification uses JWT to convey a SET, implementers SHALL NOT use SETs to convey authentication or authorization assertions.
The following is an example JWT Claims Set for a security event token (which has been formatted for readability):
{
"jti": "4d3559ec67504aaba65d40b0363faad8",
"iat": 1458496404,
"iss": "https://scim.example.com",
"aud": [
"https://scim.example.com/Feeds/98d52461fa5bbc879593b7754",
"https://scim.example.com/Feeds/5d7604516b1d08641d7676ee7"
],
"events": {
"urn:ietf:params:scim:event:create": {
"ref":
"https://scim.example.com/Users/44f6142df96bd6ab61e7521d9",
"attributes":["id", "name", "userName", "password", "emails"]
}
}
}
Figure 4: Example Event Claims
When transmitted, the above JSON body must be converted into a JWT as per [RFC7519].
The following is an example of a SCIM Event expressed as an unsecured JWT. The JOSE Header is:
{"typ":"secevent+jwt","alg":"none"}
Base64url encoding of the octets of the UTF-8 representation of the JOSE Header yields:
eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJub25lIn0
The example JWT Claims Set is encoded as follows:
eyJqdGkiOiI0ZDM1NTllYzY3NTA0YWFiYTY1ZDQwYjAzNjNmYWFkOCIsImlhdCI6MTQ1 ODQ5NjQwNCwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwiYXVkIjpbImh0 dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg3OTU5M2I3 NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYwNDUxNmIxZDA4 NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybjppZXRmOnBhcmFtczpzY2ltOmV2ZW50 OmNyZWF0ZSI6eyJyZWYiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20vVXNlcnMvNDRm NjE0MmRmOTZiZDZhYjYxZTc1MjFkOSIsImF0dHJpYnV0ZXMiOlsiaWQiLCJuYW1lIiwi dXNlck5hbWUiLCJwYXNzd29yZCIsImVtYWlscyJdfX19
The encoded JWS signature is the empty string. Concatenating the parts yields:
eyJ0eXAiOiJzZWNldmVudCtqd3QiLCJhbGciOiJub25lIn0. eyJqdGkiOiI0ZDM1NTllYzY3NTA0YWFiYTY1ZDQwYjAzNjNmYWFkOCIsImlhdCI6MTQ1 ODQ5NjQwNCwiaXNzIjoiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tIiwiYXVkIjpbImh0 dHBzOi8vc2NpbS5leGFtcGxlLmNvbS9GZWVkcy85OGQ1MjQ2MWZhNWJiYzg3OTU5M2I3 NzU0IiwiaHR0cHM6Ly9zY2ltLmV4YW1wbGUuY29tL0ZlZWRzLzVkNzYwNDUxNmIxZDA4 NjQxZDc2NzZlZTciXSwiZXZlbnRzIjp7InVybjppZXRmOnBhcmFtczpzY2ltOmV2ZW50 OmNyZWF0ZSI6eyJyZWYiOiJodHRwczovL3NjaW0uZXhhbXBsZS5jb20vVXNlcnMvNDRm NjE0MmRmOTZiZDZhYjYxZTc1MjFkOSIsImF0dHJpYnV0ZXMiOlsiaWQiLCJuYW1lIiwi dXNlck5hbWUiLCJwYXNzd29yZCIsImVtYWlscyJdfX19.
Figure 5: Example Unsecured Security Event Token
For the purpose of a simpler example in Figure 5, an unsecured token was shown. When SETs are not signed or encrypted, the Event Receiver MUST employ other mechanisms such as TLS and HTTP to provide integrity, confidentiality, and issuer validation, as needed by the application.
When validation (i.e. auditing), or additional transmission security is required, JWS signing and/or JWE encryption MAY be used. To create and or validate a signed and/or encrypted SET, follow the instructions in Section 7 of [RFC7519].
Profile Specifications for SETs define the syntax and semantics of SETs conforming to that SET profile and rules for validating those SETs. The syntax defined by profiling specifications includes what claims and event payload values are used by SETs utilizing the profile.
Defining the semantics of the SET contents for SETs utilizing the profile is equally important. Possibly most important is defining the procedures used to validate the SET issuer and to obtain the keys controlled by the issuer that were used for cryptographic operations used in the JWT representing the SET. For instance, some profiles may define an algorithm for retrieving the SET issuer's keys that uses the iss claim value as its input.
Profile Specifications MUST clearly specify the steps that a recipient of a SET utilizing that profile MUST perform to validate that the SET is both syntactically and semantically valid.
SETs may often contain sensitive information. Therefore, methods for distribution of events SHOULD require the use of a transport-layer security mechanism when distributing events. Parties MUST support TLS 1.2 [RFC5246] and MAY support additional transport-layer mechanisms meeting its security requirements. When using TLS, the client MUST perform a TLS/SSL server certificate check, per [RFC6125]. Implementation security considerations for TLS can be found in "Recommendations for Secure Use of TLS and DTLS" [RFC7525].
Security Events distributed through third-parties or that carry personally identifiable information, SHOULD be encrypted using JWE [RFC7516] or secured for confidentiality by other means.
Security Events distributed without authentication over the channel, such as via TLS ([RFC5246] and [RFC6125]), and/or OAuth 2.0 [RFC6749], or Basic Authentication [RFC7617], MUST be signed using JWS [RFC7515] so that individual events can be authenticated and validated by the Event Receiver.
This specification does not define a delivery mechanism by itself. In addition to confidentiality and integrity (discussed above), implementers and Profile Specifications MUST consider the consequences of delivery mechanisms that are not secure and/or not assured. For example, while a SET may be end-to-end secured using JWE encrypted SETs, without TLS there is no assurance that the correct endpoint received the SET and that it could be successfully processed.
As defined in this specification, there is no defined way to order multiple SETs in a sequence. Depending on the type and nature of SET event, order may or may not matter. For example, in provisioning, event order is critical -- an object could not be modified before it was created. In other SET types, such as a token revocation, the order of SETs for revoked tokens does not matter. If however, the event was described as a log-in or logged-out status for a user subject, then order becomes important.
Profiling Specifications and implementers SHOULD take caution when using timestamps such as iat to define order. Distributed systems will have some amount of clock-skew and thus time by itself will not guarantee order.
Specifications profiling SET SHOULD define a mechanism for detecting order or sequence of events. For example, the txn claim could contain an ordered value (e.g., a counter) that the issuer defines.
When SETs are delivered asynchronously and/or out-of-band with respect to the original action that incurred the security event, it is important to consider that a SET might be delivered to a Subscriber in advance or well behind the process that caused the event. For example, a user having been required to logout and then log back in again, may cause a logout SET to be issued that may arrive at the same time as the user-agent accesses a web site having just logged-in. If timing is not handled properly, the effect would be to erroneously treat the new user session as logged out. Profiling Specifications SHOULD be careful to anticipate timing and subject selection information. For example, it might be more appropriate to cancel a "session" rather than a "user". Alternatively, the specification could use timestamps that allows new sessions to be started immediately after a stated logout event time.
Because [RFC7519] states that "all claims that are not understood by implementations MUST be ignored", there is a consideration that a SET token might be confused with ID Token [OpenID.Core] if a SET is mistakenly or intentionally used in a context requiring an ID Token. If a SET could otherwise be interpreted as a valid ID Token (because it includes the required claims for an ID Token and valid issuer and audience claim values for an ID Token) then that SET profile MUST require that the exp claim not be present in the SET. Because exp is a required claim in ID Tokens, valid ID Token implementations will reject such a SET if presented as if it were an ID Token.
Excluding exp from SETs that could otherwise be confused with ID Tokens is actually defense in depth. In any OpenID Connect contexts in which an attacker could attempt to substitute a SET for an ID Token, the SET would actually already be rejected as an ID Token because it would not contain the correct nonce claim value for the ID Token to be accepted in that context.
Note that the use of explicit typing, as described in Section 2.2, will not achieve disambiguation between ID Tokens and SETs, as the ID Token validation rules do not use the typ header parameter value.
OAuth 2.0 [RFC6749] defines access tokens as being opaque. Nonetheless, some implementations implement access tokens as JWTs. Because the structure of these JWTs is implementation-specific, ensuring that a SET cannot be confused with such an access token is therefore likewise, in general, implementation specific. Nonetheless, it is recommended that SET profiles employ the following strategies to prevent possible substitutions of SETs for access tokens in contexts in which that might be possible:
JWTs are now being used in application areas beyond the identity applications in which they first appeared. For instance, the Session Initiation Protocol (SIP) Via Header Field [RFC8055] and Personal Assertion Token (PASSporT) [I-D.ietf-stir-passport] specifications both define JWT profiles that use mostly or completely different sets of claims than are used by ID Tokens. If it would otherwise be possible for an attacker to substitute a SET for one of these (or other) kinds of JWTs, then the SET profile must be defined in such a way that any substituted SET will result in its rejection when validated as the intended kind of JWT.
The most direct way to ensure that a SET is not confused with another kind of JWT is to have the JWT validation logic reject JWTs containing an events claim unless the JWT is intended to be a SET. This approach can be employed for new systems but may not be applicable to existing systems.
Another direct way to prevent confusion is to employ explicit typing, as described in Section 2.2, and modify applicable token validation systems to use the typ header parameter value. This approach can be employed for new systems but may not be applicable to existing systems.
For many use cases, the simplest way to prevent substitution is requiring that the SET not include claims that are required for the kind of JWT that might be the target of an attack. For example, for [RFC8055], the sip_callid claim could be omitted and for [I-D.ietf-stir-passport], the orig claim could be omitted.
In many contexts, simple measures such as these will accomplish the task, should confusion otherwise even be possible. Note that this topic is being explored in a more general fashion in JSON Web Token Best Current Practices [I-D.sheffer-oauth-jwt-bcp]. The proposed best practices in that draft may also be applicable for particular SET profiles and use cases.
If a SET needs to be retained for audit purposes, JWS MAY be used to provide verification of its authenticity.
Event Transmitters SHOULD attempt to specialize feeds so that the content is targeted to the specific business and protocol needs of subscribers.
When sharing personally identifiable information or information that is otherwise considered confidential to affected users, Event Transmitters and Receivers MUST have the appropriate legal agreements and user consent or terms of service in place.
The propagation of subject identifiers can be perceived as personally identifiable information. Where possible, Event Transmitters and Receivers SHOULD devise approaches that prevent propagation -- for example, the passing of a hash value that requires the subscriber to already know the subject.
This specification registers the events and txn claims in the IANA "JSON Web Token Claims" registry [IANA.JWT.Claims] established by [RFC7519].
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.
The editors would like to thank the members of the IETF SCIM working group, which began discussions of provisioning events starting with draft-hunt-scim-notify-00 in 2015.
The editors would like to thank the participants in the IETF id-event mailing list and related working groups for their support of this specification.
From the original draft-hunt-idevent-token:
Draft 01 - PH - Renamed eventUris to events
Draft 00 - PH - First Draft
Draft 01 - PH - Fixed some alignment issues with JWT. Remove event type attribute.
Draft 02 - PH - Renamed to Security Events, removed questions, clarified examples and intro text, and added security and privacy section.
Draft 03 - PH events claim, and proof-reading corrections.
- mbj - Registered
Draft 04 - PH -
Draft 05 - PH - Fixed find/replace error that resulted in claim being spelled claimc
Draft 06 - PH -
Draft 07 -
Draft 08 - PH -
From draft-ietf-secevent-token:
Draft 00 - PH - First WG Draft based on draft-hunt-idevent-token
Draft 01 - PH - Changes as follows:
Draft 02 - Changes are as follows: