| OAuth Working Group | W. Denniss |
| Internet-Draft | |
| 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
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.
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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 users, dishonest apps, or compromised devices, but the signal format described could carry signals that do.
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.
In addition to the terms defined in referenced specifications, this document uses the following terms:
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:
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
}
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:
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.
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:
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 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:
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.
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.
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.
This specification registers the following value in the IANA "OAuth Parameters" registry [IANA.OAuth.Parameters] established by [RFC6749].
This specification registers the following error in the IANA "OAuth Extensions Error Registry" [IANA.OAuth.Parameters] established by [RFC6749].
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.
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].
| [IANA.OAuth.Parameters] | IANA, "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. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, DOI 10.17487/RFC5226, May 2008. |
| [RFC6749] | Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012. |
| [RFC6819] | Lodderstedt, T., McGloin, M. and P. Hunt, "OAuth 2.0 Threat Model and Security Considerations", RFC 6819, DOI 10.17487/RFC6819, January 2013. |
The following individuals contributed ideas, feedback, and wording that shaped and formed the final specification:
Eric Sachs, John Bradley, and Andy Zmolek.