Internet DRAFT - draft-wdenniss-oauth-device-posture
draft-wdenniss-oauth-device-posture
OAuth Working Group W. Denniss
Internet-Draft Google
Intended status: Standards Track KM. McGuinness
Expires: May 17, 2018 Okta
J. Bradley
Yubico
November 13, 2017
OAuth 2.0 Device Posture Signals
draft-wdenniss-oauth-device-posture-01
Abstract
Enterprise and security focused OAuth providers typically want
additional signals to confirm user presence when users return to
previously authorized apps. Rather than requiring a full
reauthentication, or require enrollment in a mobile device management
solution, some authorization servers may be willing to accept device
posture signals from the app, like the fact that device has a lock
screen, as confirmation of user presence. This document details how
OAuth native app clients can communicate device posture signals to
OAuth providers.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 17, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Device Posture Signal Dictionary . . . . . . . . . . . . . . 3
5. Authorization Request Device Posture Hint . . . . . . . . . . 5
6. Token Endpoint Device Posture Enforcement . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7.1. Device Posture Scope . . . . . . . . . . . . . . . . . . 6
7.2. Spoofed Devices . . . . . . . . . . . . . . . . . . . . . 6
7.3. App Trustworthiness . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8.1. OAuth Parameters Registration . . . . . . . . . . . . . . 7
8.1.1. Registry Contents . . . . . . . . . . . . . . . . . . 7
8.2. OAuth Extensions Error Registration . . . . . . . . . . . 7
8.2.1. Registry Contents . . . . . . . . . . . . . . . . . . 7
8.3. Device Posture Keys Registry . . . . . . . . . . . . . . 7
8.3.1. Registration Template . . . . . . . . . . . . . . . . 8
8.3.2. Initial Registry Contents . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Users who follow strong security practices on their devices - such as
configuring screen locks, and not enabling admin privileges (commonly
known as "rooting" or "jailbreaking") - shouldn't need to
reauthenticate frequently to the individual apps on their device.
This specification details how apps can send device posture signals
to the OAuth Token Endpoint, enabling it to enforce device policy
compliance, and avoid the need for reauthentication in some cases.
It is designed to provide a mechanism for honest apps to communicate
device posture. By itself it doesn't protect against malicious
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users, dishonest apps, or compromised devices, but the signal format
described could carry signals that do.
2. 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 Key
words for use in RFCs to Indicate Requirement Levels [RFC2119]. If
these words are used without being spelled in uppercase then they are
to be interpreted with their normal natural language meanings.
3. Terminology
In addition to the terms defined in referenced specifications, this
document uses the following terms:
MDM
Mobile Device Management.
EMM
Enterprise Mobility Management.
4. Device Posture Signal Dictionary
The device posture is a dictionary of signals asserted by the app
about the device. The structure is send as an added parameter in
several places during the OAuth flow, as documented in the subsequent
sections.
All device posture keys are OPTIONAL and MUST only be set when the
attribute can be obtained by the app. The standard attribute keys
are as follows:
screen_lock
Boolean. True if the device has a screen lock, such as a pin,
pattern biometric, etc.
root_privileges
Boolean. True if user apps can access root device privileges.
For mobile operating systems, known as "jailbreaking" on iOS and
"rooting" on Android.
full_disk_encryption
Boolean. True if data stored on the device is fully encrypted at
rest.
device_id
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String. A unique identifier for the device.
device_os
String. The name of the operating system running on the device
such as "iOS" or "Android".
device_os_version
String. The current version of the operating system.
device_vendor
String. The vendor of the device such as "Apple" or "Google".
device_model
String. The model of the device such as "iPhone X" or "Pixel 2".
device_attestation
Dictionary. An attestation from the operating system, containing
a signed-statement about the device and/or the app. The format is
a dictionary, the specifics of which depends on the operating
system.
app_id
String. The platform-specific identifier (URI) for the
application. For Android, the format of the URI is android:apk-
key-hash:<hash-of-apk-signing-cert>. For iOS, the format of URI
is ios:bundle-id:<ios-bundle-id-of-app>.
app_managed
Boolean. True if the app is managed by a MDM/EMM system.
An example device posture dictionary:
{
"screen_lock": true,
"root_privileges": false,
"full_disk_encryption": true,
"device_id": "6bdde1e8-0667-40f9-9993-16aa52ee6b38",
"device_os": "iOS",
"device_os_version": "11.1",
"device_vendor": "Apple",
"device_model": "iPhone X",
"app_id": "ios:bundle-id:com.example.myapp",
"app_managed": false
}
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5. Authorization Request Device Posture Hint
Clients MAY send the device posture signal dictionary to the
authorization server in the authorization request. These signals,
except for those that are signed and bound to the device are
susceptible to client-side modification by end-users. While
untrusted, such signals can still be used as hints by the
authorization server to present a better user experience, like
informing the user they need a lock screen.
Error encountered during authorization can be displayed to the user
in the browser making this a more user friendly way to instruct the
user on how to move their device into conformance. The token
endpoint (on which errors are less user-friendly as there's no user
agent), can then enforce the restrictions per Section 6.
The following parameters are added to the OAuth 2.0 Authorization
Request or the OpenID Connect Authorization Request:
device_posture_hint
JSON String. URL-encoded JSON dictionary, contains the Device
Posture Signals defined in Section 4.
A AS receving device_posture_hint may pass the value on to upstream
OpenID Connect IDP using the same paramater to enable the
Authentication Server to make policy decisions.
6. Token Endpoint Device Posture Enforcement
Clients that follow this specification MUST send the device posture
signals on every request to the token endpoint.
Token Endpoints SHOULD verify that the posture conforms to their
requirements and act accordingly.
The following parameters are added to all requests to the Token
Endpoint:
device_posture
JSON String. URL-encoded JSON dictionary, contains the Device
Posture Signals defined in Section 4.
The app MUST obtain fresh device posture information before every
request to the Token Endpoint, and MUST NOT include stale information
(rather, it should drop any signals it cannot freshly obtain).
For token refresh requests, where the device posture has been
previously communicated, if an attribute is missing, the Token
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Endpoint may choose to use the previous value, based on it's own
policy and freshness requirements.
If the policy does not meet requirements, the Token Endpoint SHOULD
return the following error code:
device_posture_invalid
Error indicating that the device posture does not meet
requirements. The error description SHOULD contain details on why
this is is the case.
7. Security Considerations
7.1. Device Posture Scope
This specification is designed to help authorization servers enforce
security policy (like requiring a lock screen) on end-users. The
intent is to enforce restrictions on honest users, to force them to
follow security practices set out by the authorization server. By
itself, it offers no protection against malicious users, dishonest
apps, or compromised devices.
Combined with other technologies like device-based attestations and
token binding may enable such protection, and this specification
could be used to transmit secure signals, but that topic is out of
scope for this specification.
7.2. Spoofed Devices
It is possible to at a device level completely spoof the device
posture. Even statements signed by the operating system are
vulnerable to spoofing, as it's possible a statement from the real
device can be replayed on a spoofed device, unless such statements
include a binding to the device itself. Per Section 7.1, this topic
is out of scope for this specification.
7.3. App Trustworthiness
This specification is designed to allow trusted apps to report device
posture to the authorization server to help the server enforce
security policy on end-users. It does not by itself force apps to be
honest, or genuine. Genuine apps (i.e. apps not lying about their
client ID) might be dishonest about the device posture, and apps that
are normally honest, could be spoofed, unless anti-spoofing
countermeasures that are out of scope of this specification are
employed.
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8. IANA Considerations
8.1. OAuth Parameters Registration
This specification registers the following value in the IANA "OAuth
Parameters" registry [IANA.OAuth.Parameters] established by
[RFC6749].
8.1.1. Registry Contents
o Parameter name: device_posture_hint
o Parameter usage location: authorization request
o Change controller: IESG
o Specification document(s): Section 5 of [[ this specification ]]
o Parameter name: device_posture
o Parameter usage location: token request
o Change controller: IESG
o Specification document(s): Section 6 of [[ this specification ]]
8.2. OAuth Extensions Error Registration
This specification registers the following error in the IANA "OAuth
Extensions Error Registry" [IANA.OAuth.Parameters] established by
[RFC6749].
8.2.1. Registry Contents
o Error name: device_posture_invalid
o Error usage location: authorization response, token error response
o Related protocol extension: resource parameter
o Change controller: IESG
o Specification document(s): Section 6 of [[ this specification ]]
8.3. Device Posture Keys Registry
This specification establishes the IANA "Device Posture Keys"
registry for Device Posture Dictionary keys. The registry records
the Device Posture key and a reference to the specification that
defines it. This specification registers the Device Posture keys
defined in Section 4.
Keys are registered on an Expert Review [RFC5226] basis after a
three-week review period on the oauth-reg-review@ietf.org mailing
list, on the advice of one or more Designated Experts.
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Registration requests sent to the mailing list for review should use
an appropriate subject (e.g., "Request to register Device Posture
Key: screen_lock").
Within the review period, the Designated Experts will either approve
or deny the registration request, communicating this decision to the
review list and IANA. Denials should include an explanation and, if
applicable, suggestions as to how to make the request successful.
Registration requests that are undetermined for a period longer than
21 days can be brought to the IESG's attention (using the
iesg@ietf.org mailing list) for resolution.
Criteria that should be applied by the Designated Experts includes
determining whether the proposed registration duplicates existing
functionality, whether it is likely to be of general applicability or
whether it is useful only for a single application, whether the value
is actually being used, and whether the registration description is
clear.
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the review mailing
list.
It is suggested that the same Designated Experts evaluate these
registration requests as those who evaluate registration requests for
the IANA "OAuth Parameters" registry [IANA.OAuth.Parameters].
8.3.1. Registration Template
Device Posture Signal Key:
The key name requested (e.g., "screen_lock"). Names may not match
other registered names in a case-insensitive manner unless the
Designated Experts state that there is a compelling reason to
allow an exception.
Device Posture Signal Key Description:
Brief description of the device posture signal (e.g., "Screen lock
active").
Change Controller:
For Standards Track RFCs, state "IESG". For others, give the name
of the responsible party. Other details (e.g., postal address,
email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the parameter,
preferably including URIs that can be used to retrieve copies of
the documents. An indication of the relevant sections may also be
included but is not required.
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8.3.2. Initial Registry Contents
o Device Posture Signal Key: "screen_lock"
o Device Posture Signal Key Description: Boolean. 'true' when the
device has a screen lock enabled.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "root_privileges"
o Device Posture Signal Key Description: Boolean. True if user apps
can access root device privileges.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "full_disk_encryption"
o Device Posture Signal Key Description: Boolean. True if data
stored on the device is fully encrypted at rest.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "device_id"
o Device Posture Signal Key Description: String. A unique
identifier for the device.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "device_os"
o Device Posture Signal Key Description: String. The name of the
operating system running on the device such as "iOS" or "Android".
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "device_os_version"
o Device Posture Signal Key Description: String. The current
version of the operating system.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "device_vendor"
o Device Posture Signal Key Description: String. The vendor of the
device such as "Apple or "Google".
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "device_model"
o Device Posture Signal Key Description: String. The model of the
device such as "iPhone X" or "Pixel 2"
o Change Controller: IESG
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o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "device_attestation"
o Device Posture Signal Key Description: Dictionary. An attestation
from the operating system, containing a signed-statement about the
device and/or the app.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "app_id"
o Device Posture Signal Key Description: String. The platform-
specific identifier (URI) for the application. For Android, the
format of the URI is android:apk-key-hash:<hash-of-apk-signing-
cert>. For iOS, the format of URI is ios:bundle-id:<ios-bundle-
id-of-app>.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
o Device Posture Signal Key: "app_managed"
o Device Posture Signal Key Description: Boolean. True if the app
is managed by a MDM/EMM system.
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this specification ]]
9. References
9.1. Normative References
[IANA.OAuth.Parameters]
IANA, "OAuth Parameters",
<http://www.iana.org/assignments/oauth-parameters>.
[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>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[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>.
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9.2. Informative References
[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819,
DOI 10.17487/RFC6819, January 2013,
<https://www.rfc-editor.org/info/rfc6819>.
Appendix A. Acknowledgements
The following individuals contributed ideas, feedback, and wording
that shaped and formed the final specification:
Eric Sachs, John Bradley, and Andy Zmolek.
Authors' Addresses
William Denniss
Google
1600 Amphitheatre Pkwy
Mountain View, CA 94043
USA
Phone: +1 650-253-0000
Email: wdenniss@google.com
URI: http://google.com/
Karl McGuinness
Okta
301 Brannan St.
San Francisco, CA 94107
USA
Email: kmcguinness@okta.com
URI: https://www.okta.com/
John Bradley
Yubico
530 Lytton Ave, Suite 301
Palo Alto, CA 94301
USA
Phone: +1 202-630-5272
Email: ietf@ve7jtb.com
URI: https://www.thread-safe.com/
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