Internet DRAFT - draft-ietf-abfab-usability-ui-considerations
draft-ietf-abfab-usability-ui-considerations
ABFAB R. Smith
Internet-Draft Cardiff University
Intended status: Informational M. Donnelly
Expires: September 22, 2016 Painless Security
March 21, 2016
Application Bridging for Federated Access Beyond web (ABFAB) Usability
and User Interface Considerations
draft-ietf-abfab-usability-ui-considerations-04
Abstract
The real world use of ABFAB-based technologies requires that any
identity that is to be used for authentication has to be configured
on the ABFAB-enabled client device. Achieving this requires software
on that device (either built into the operating system or a
standalone utility) that will interact with the user, managing their
identity information and identity-to-service mappings. All designers
of software to fulfil this role will face the same set of challenges.
This document aims to document these challenges with the aim of
producing well-thought out UIs with some degree of consistency
between implementations.
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
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 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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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Considerations around Terminology . . . . . . . . . . . . . . 5
5.1. Identity . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Services . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Identity to Service Mapping . . . . . . . . . . . . . . . 6
6. Considerations around Management of Identities . . . . . . . 7
6.1. Information associated with each Identity . . . . . . . . 7
6.2. Information associated with each Identity Provider . . . 8
6.3. Storage of Identity Information . . . . . . . . . . . . . 9
6.4. Adding/Association of an Identity . . . . . . . . . . . . 10
6.4.1. Identity Provider Addition . . . . . . . . . . . . . 10
6.4.2. Identity Addition . . . . . . . . . . . . . . . . . . 12
6.5. Modifying Identity Information . . . . . . . . . . . . . 14
6.5.1. Manual Modification . . . . . . . . . . . . . . . . . 14
6.5.2. Automated Modification . . . . . . . . . . . . . . . 15
6.6. Verifying an identity . . . . . . . . . . . . . . . . . . 15
6.7. Removing an Identity . . . . . . . . . . . . . . . . . . 15
6.7.1. Manual Removal . . . . . . . . . . . . . . . . . . . 15
6.7.2. Automated Removal . . . . . . . . . . . . . . . . . . 16
6.8. Storing an Identity with or without credentials . . . . . 16
7. Considerations around Management of Service to Identity
Mappings . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Associating a Service with an Identity . . . . . . . . . 17
7.1.1. User-driven Manual Association . . . . . . . . . . . 17
7.1.2. Automated Rules-based Association . . . . . . . . . . 17
7.1.3. Association Conflicts . . . . . . . . . . . . . . . . 17
7.2. Disassociating a Service with an Identity . . . . . . . . 18
7.3. Listing Services and Identities . . . . . . . . . . . . . 19
7.4. Showing the Service that is requesting Authentication . . 19
7.5. Showing the Identity currently in use . . . . . . . . . . 19
7.6. Multiple Identities for a Particular Service . . . . . . 20
7.7. Not using ABFAB for a Particular Service . . . . . . . . 20
8. Handling of Errors . . . . . . . . . . . . . . . . . . . . . 20
8.1. Errors in GSS-API . . . . . . . . . . . . . . . . . . . . 20
8.1.1. Log of Errors . . . . . . . . . . . . . . . . . . . . 21
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8.2. Examples of errors . . . . . . . . . . . . . . . . . . . 21
9. Handling of Successes . . . . . . . . . . . . . . . . . . . . 22
9.1. Reporting Authentication Success on First Use of Identity 22
9.2. Reporting Authentication Success . . . . . . . . . . . . 22
10. Other Considerations . . . . . . . . . . . . . . . . . . . . 22
10.1. Identity Selector Taking Focus . . . . . . . . . . . . . 22
10.2. Import/Export of Credentials . . . . . . . . . . . . . . 22
11. Security Considerations . . . . . . . . . . . . . . . . . . . 23
12. Privacy Considerations . . . . . . . . . . . . . . . . . . . 24
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
16.1. Normative References . . . . . . . . . . . . . . . . . . 25
16.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 27
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
The use of ABFAB-based technologies requires that any identity that
is to be used for authentication has to be configured on the client
device. Achieving this requires software on that device (either
built into the operating system or a standalone utility) that will
interact with the user, and manage the user's identities and
credential-to-service mappings. Anyone designing that software will
face the same set of challenges.
This document does not intend to supplant evidence-based UI design
guidelines; implementers of identity selectors are strongly
encouraged to understand the latest in HCI and UX thought and
practice. Instead, it aims to document the common challenges faced
by implementers with the aim of providing a common starting point for
implementers in the hope that this aids in producing well-thought out
UIs with some degree of consistency.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Terminology
Various items of terminology used in the document are heavily
overloaded in that they mean a variety of different things to
different people. In an attempt to minimise this problem, this
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section gives a brief description of the main items of terminology
used in order to aid a consistent understanding of this document.
o NAI: Network Access Identifier - a standard way of identifying a
user and assisting in the routing of an authentication request
(see [RFC4282]).
o Identity: In this context, an identity is a credential given to a
user by a particular organisation with which they have an
association. A user may have multiple identities - potentially
multiple identities per organisation, and also across multiple
organisations. Each identity will consist of an NAI, alongside
other information that supports authentication. Note that in
other contexts the usual use of "identity" would match our use of
"user", whereas the usual use of "identifier" matches our use of
identity.
o Service: The thing that the user is attempting to authenticate to
via ABFAB technology. See [I-D.ietf-abfab-usecases] for some
example ABFAB use cases. Also known as the Relying Party.
o Identity Provider: The thing able to make access management
decisions about the Identity.
o Identity Selector: A piece of software that enables the process by
which the GSS-API acquires the identity to use with a particular
service. An Identity Selector typically would allow the user to
configure a set of identities along with service to identity
mappings.
o Trust anchor: An authoritative source of verification of a
particular ABFAB Identity Provider, used to allow authentication
of an Identity Provider using X.509 [RFC5280]. Typically this
will be a commercial CA to allow authentication via chain of
trust, or a preconfigured non-commercial certificate (e.g. self-
signed).
o Credential: Whatever is used by the user to authenticate
themselves with a particular NAI. What exactly this will be will
be dependent on the EAP method being used, but is likely to be
something like a password or a certificate.
4. Context
When using the ABFAB architecture (see [I-D.ietf-abfab-arch]) to
perform federated authentication to some service, a user will need to
provide identity information that they wish to use to authenticate to
that particular service. This will happen through a process of the
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application calling the GSS-API, which will in turn gather the user's
credentials through some process. We will call this process the
"identity selector" in this document (though note that this is not a
recommendation on terminology for the process).
The simplest way to achieve the desired effect would be a process
that simply takes the credentials from the currently logged in user
(e.g. the Windows Domain Credentials) and uses those for all services
that request authenticate through ABFAB. This approach gives
ultimate simplicity in terms of UI (it wouldn't have one) but the
least flexibility (the user has to use a single identity for
everything). If there is ever to be a requirement for a user to use
a different set of credentials for a service, or a requirement for
the user to use ABFAB to authenticate to the operating system, then
something more complex will be needed.
Where there is a requirement for multiple credentials to be
supported, there are at least two methods that could be employed to
configure identities and associated information:
o They could be configured manually by the user in a configuration
file that could be edited by hand or some such simple process, and
read by the GSS-API mechanism. While this could work very well
functionally, in practice only a small subset of users would be
happy with - and able to - configure their identities in such a
manner.
o They could be configured through some interactive process. For
ease of use this should have a simple UI, although to support some
use cases a headless mode (i.e. a way of interacting with the
identity selector when there is no GUI present) may need to be
supported.
When designing an identity selector with a UI (or indeed, with a
headless mode), any implementer will share a common set of usability
considerations inherent to the context. This document aims to
explore these considerations, and provide advice and guidance on
addressing them where possible.
5. Considerations around Terminology
Anyone designing an identity selector will have to grapple with
choosing terminology that the average user has some chance of
understanding. This terminology can split into a few main functional
areas, as discussed next.
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5.1. Identity
The first area where terminology is needed is around the identity/
identities of the user. Users are typically used to seeing a variety
of terms for aspects of their identity in the federated sense, and an
even larger variety in the wider Internet sense. For example, in the
federated sense some of these terms include "username", "login",
"network account", "institutional account", "home organisation
account", "credentials", and a myriad of other such terms. However,
NAI - the technically correct name for their identity in an ABFAB
sense - is highly unlikely to be one of these terms that users are
used to seeing. Further, given that the NAI superficially looks like
an email address, there is a definite potential for confusion.
Implementers of an identity selector will need to carefully consider
their intended audience for both their level of technical capability
and the existing terminology that they may have been exposed to.
Beyond terminology, careful thought needs to be given to the paradigm
to use when presenting identity to users, as identities and services
are abstract concepts that some users may not find easily
understandable. Implementers may wish to keep such abstract concepts
despite this, or may wish to examine attempts to map to real world
paradigms, e.g. the idea of using "Identity Cards" that are held in
the user's "Wallet", as used by the now defunct Microsoft Cardspace
([MS-CS]).
5.2. Services
Terminology around services is likely to be less of a problem than
identity, but it will actually depend on what the service is. For
example, each service could be simply described as "server",
"system", etc. But for simplicity just the word "service" will
probably usually suffice.
5.3. Identity to Service Mapping
The basic functionality of the Identity Selector is to create the
correct combination of Identity and Service, so that the correct
identity is chosen to create the credential for the GSS-EAP
connection with the given service. Mapping is the process of
creating this relationship between identity and service.
Depending on your perspective either each identity may be mapped to
multiple services, or each service has multiple identities mapped to
it. Thus any UI could present either perspective, or both.
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6. Considerations around Management of Identities
One of the core features of an identity selector is the management of
a user's identities. This section first looks at what information
associated with an identity will need to manage, and then looks in
detail at various usability considerations of this area.
6.1. Information associated with each Identity
The bare minimum set of information that MUST be stored about each
identity to allow ABFAB authentication to take place is a single
item:
o NAI: The user's Network Access Identifier (see [RFC4282]) for this
particular credential. For example, "joe@example.com". Note that
the identity selector MUST NOT store different identities that use
the same NAI. This is required as the NAI is the unique key that
is used by the identity selector when interacting with the GSS-API
mechanism for various reasons, for example, to allow the GSS-API
mechanism to report back error or success statuses or to allow the
application to request the use of a specific identity.
Next up is a small set of information that SHOULD be stored about
each identity to allow the user to effectively select a particular
identity:
o Identity provider realm: The ABFAB realm of the identity provider.
This is used as a key to look up the identity provider from the
identity selector's list of identity providers, in order to access
the trust anchor during verification of the identity provider.
o Credential: Whatever is used by the users to authenticate
themselves with a particular NAI. What exactly this will be will
be dependent on the EAP method being used, but is likely to be
something like a password or a certificate. Note that the
identity selector SHOULD allow a user to store the credential.
However, there are use cases where a user may specifically opt for
this not to be "remembered", so the identity selector MUST NOT
store the credential without confirmation from the user.
Finally, there is a set of optional information that MAY be stored
about each identity that represent useful information for the user to
have and could make an identity selector more usable. Note that this
list is neither intended to be exhaustive or even particularly
correct; any implementer is free to use whatever make sense in their
implementation and conforms to good HCI/UX guidelines. Instead, it
is simply a suggested starting point.
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o Friendly name for identity: To allow the user to differentiate
between the set of identities represented in the Identity
Selector. This should be editable by the user. The only
restriction on this name is that it MUST be unique within that
particular user's set of identities. For example: "Student
username", "Google Account", "Work Login", etc.
o Friendly icon for identity: To allow the user to differentiate
between the set of identities they have they should be able to set
an icon for that particular identity.
o Password changing URL: The URL the user should visit should they
need to change their password for this particular identity. For
example, "http://www.example.com/passwordreset?identifier=myId".
o Helpdesk URL: The URL this particular identity should visit to get
contact details for the helpdesk of the organisation that issued
this particular identity for when the user encounters issues and
needs help. For example, https://www.example.com/
helpdesk?identifier=myId.
6.2. Information associated with each Identity Provider
Identity providers are entities that may be shared across multiple
identities. For instance, a person at a university may have one
identity as a student and another identity as an employee, but a
single identity provider makes access management decisions about
both. In these cases, the identity selector MUST consider it an
error if the trust anchor for the identity provider is different
between the various identities managed by the single identity
provider.
The bare minimum set of information that MUST be stored about each
identity provider is:
o Realm: The realm of the identity provider. This will uniquely
identify the identity realm.
o Trust anchor: For the identity selector to be able to verify that
the Identity Provider it is going to talk to and attempt to
authenticate against is the Identity Provider that it is
expecting, and that it is not being spoofed in some way. This is
likely to be an X.509 certificate [RFC5280], or a tuple of
(trusted root certificate, servername in Subject or
subjectAltName). Storing a credential without a relevant trust
anchor allows for the possibility of a malicious attacker
intercepting traffic and masquerading as the Identity Provider in
question.
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Identity providers also have a set of optional information that MAY
be stored about each identify provider. This set includes, but is
not limited to:
o Friendly name for the identity provider: To allow the user to
differentiate between the set of identity providers represented in
the Identity Selector. This should be editable by the user. The
only restriction on this name is that it MUST be unique within
that particular user's set of identity providers. For example:
"My University", "Google", etc.
o Friendly icon for the identity provider: To allow the user to
differentiate between the set of identity providers they have they
should be able to set an icon for that particular identity
provider.
o Password changing URL: The URL the user should visit should they
need to change passwords for identities in this realm. For
example, "http://www.example.com/passwordreset".
o Helpdesk URL: The URL the user should visit to get contact details
for the helpdesk of the organisation that issued this particular
identity for when the user encounters issues and needs help. For
example, https://www.example.com/helpdesk.
Note that the password changing URL and helpdesk URL somewhat mirror
the definitions of the same fields in the identity. The distinction
is that the URLs in the identity SHOULD apply to the individual
identity, whereas the URLs in the identity provider SHOULD apply to
all identities that the identity provider defines. For example, an
identity password change URL would provide a personalized experience
of changing the password for the given identity, but the identity
provider password change URL would direct the user to a page where
the user would need to enter the individual identity that needs a new
password.
If the identity contains no password change URL or helpdesk URL, the
identity selector MAY present any corresponding URL from the identity
selector instead. However, if the identity contains the URL, the
identity selector SHOULD present the URL from the identity.
6.3. Storage of Identity Information
Since some of the information that makes up the identity is sensitive
in nature (e.g. containing passwords), then this information SHOULD
be stored and accessed securely. This might involve ensuring the
credential information is held in encrypted form on device and
accessed using a passphrase. For deeper integration into the system,
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this could be done by using existing secure storage on the system
such as Keychain on a Mac, the GNOME keyring on a GNOME based Linux
device, or the Credentials Manager on Windows.
6.4. Adding/Association of an Identity
Users will have one or more identities given to them by organisations
that they have a relationship with. One of the core tasks of an
identity selector will be to learn about these identities and their
identity providers in order to use them when it comes to
authenticating to services on behalf of the user. Adding these
identities could be done in one of three ways: manual addition,
automated addition that is manually triggered, or automated addition
that is automatically triggered. Each of these are discussed in more
detail next.
Note that the term "association" or "addition" of an identity is used
rather than "provisioning" of an identity, because while we actually
are provisioning identities into the UI, provisioning is an
overloaded term in the identity and access management space and could
easily be confused with identity provisioning in the sense of the
creation of the identity by the home organisation's identity
management procedures.
6.4.1. Identity Provider Addition
6.4.1.1. Manual Identity Provider Addition
Allowing users to add an identity provider manually is technically
the easiest method to get this information, but it is a method that
has the greatest usability drawbacks - including some that create
potential security issues. Most of the information required is
relatively technical and finding some way of explaining what each
field is to an non-technical audience is challenging (to say the
least). This especially is the case for trust anchor information.
Thus this method should be considered as a power-user option only, or
as a fall-back should the other methods not be applicable.
Implementers may well decide not to offer the manual option due to
these drawbacks.
When this method is used, careful consideration should be given to
the UI presented to the user. The UI will have to ask for all of the
information detailed in Section 6.2.
Trust anchors present a particularly onerous challenge for the user
to enter. For this reason, many identity selectors will want to
implement a leap-of-faith acquisition of the trust anchor. For these
leap of faith acquisitions, the identity selector SHOULD present the
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user with the name of the realm that the identity selector is
attempting to reach, the subject of the trust anchor certificate,
details of the certification chain, and a fingerprint of the
certificate. If the realm does not match the subject of the
certificate, the identity selector MUST inform the user of the
discrepency. The identity selector MAY reject the leap-of-faith on
its own, or MAY allow the user to proceed anyway. If the user
proceeds anyway, the identity selector SHOULD urge the user to reject
the leap-of-faith.
The area of verification of trust anchors is very important. An
Identity Selector that allows for manual addition of identity
provider information SHOULD try to ensure that trust anchor
information is gathered and checked in a secure a manner as possible
- where users have to enter and confirm all trust anchor information,
or be required to explicitly agree to an insecure configuration if
this is not done properly.
6.4.1.2. Manually Triggered Automated Identity Provider Addition
One way to bypass the need for manual addition of an identity
provider - and all of the usability and security issues inherent with
that approach - is to provide some sort of manually triggered, but
automated, addition process. One approach to accomplishing this, for
example, could be for an organisation to have a section on their
website where their users could visit and be given piece of data that
contains much or all of the relevant identity provider information
for importing into the identity selector.
Additionally, the user SHOULD be given the opportunity to:
o Supply or change the default friendly name and friendly icon for
that identity provider - to allow the user to customise the
identifier they use for that identity provider;
o Reject the addition of the identity provider completely - to allow
the user to back out of the association process in an intuitive
way.
In this case, trust anchors would be directly provided through the
automated addition process to help establish the trust relationship
in a secure manner.
6.4.1.3. Fully Automated Identity Provider Addition
Many organisations manage the machines of their users using
enterprise management tools. Such organisations may wish to be able
to automatically add a particular user's identity provider to the
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identity selector on their machine/network account so that the user
has to do nothing.
This represents the best usability for the user - who wouldn't
actually have to do anything. However, it can only work on machines
centrally managed by the organisation.
6.4.2. Identity Addition
6.4.2.1. Manual Identity Addition
Allowing users to add an identity manually is relatively easy in
comparison to adding an identity provider manually. If the identity
provider is already known in the identity selector, then the identity
selector can construct the NAI from the identity provider and a
username. Thus the manual addition of an identity in a known realm
needs to prompt the user only to pick the realm, to enter the
username, and to enter the credential. If the identity provider is
not known to the identity selector, the identity selector will
provide the user with a way to define a new one as part of the
identity addition.
There are two points at which a user could manually add an identity:
o Asynchronously: the user could be allowed to, at any time, trigger
a workflow of manually adding an identity. This represents the
most flexible way of adding an identity since a user can perform
this at any time. It does, however, also have inherent issues
when it comes to verifying the newly added identity - see
Section 6.6.
o Just In Time: when connecting to a service which has no mapping to
an existing identity, the user could be given an option to add a
new one, as well as associating with an existing one. This seems
to present a better user experience when it comes to verifying the
newly added identity (see Section 6.6), however, it represents a
less direct method of adding an identity. Users who have not yet
added the appropriate identity to their identity selector may find
it difficult to understand that they must try to access a
particular service in order to add an identity.
Of course, implementers could support both styles of identity
addition to gain the benefits of both and give flexibility to the
user.
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6.4.2.2. Manually Triggered Automated Identity Addition
Much like in the case of the manually triggered automated identity
provider addition Section 6.4.1.2, an identity could be added to the
identity selector through a user-initiated mechanism. To follow the
example in the identity provider section above, the organization
could enhance the identity provider addition web service to prompt
for the user part of the NAI. The web service could then generate
all of the data needed for adding both the identity provider and the
identity.
It is reasonable to assume that any such automated addition service
is likely to be organisation specific, so that the Issuing
Organisation and realm part of the NAI will be constant, as would be
the trust anchor information. The user part of their NAI will have
been input on the web service. The password could be provided as a
part of the provided data or the identity selector could prompt the
user to enter it.
If the identity provider data contained in this identity to be added
conflicts with an existing identity provider known to the identity
selector, the identity selector SHOULD present the discrepency to the
user. The identity selector MAY reject the identity provider and
identity on its own, or MAY allow the user to proceed anyway. If the
identity selector allows the user to proceed anyway, the identity
selector SHOULD urge the user to reject the leap-of-faith, and
require the user to confirm the intent to proceed before proceeding.
Additionally, the user SHOULD be given the opportunity to:
o Supply or change the default friendly name for that identity - to
allow the user to customise the identifier they use for that
identity;
o Indicate whether or not the identity selector should always ask
before using services with this identity - to customise the way in
which the identity selector interacts with the user with this
particular identity;
o Reject the addition of the identity completely - to allow the user
to back out of the association process in an intuitive way.
6.4.2.3. Fully Automated Identity Addition
Section Section 6.4.1.3 introduced the concept of using enterprise
management tools to add an identity provider to the identity
selector. These enterprise management tools could be used to add an
identity that uses the identity provider added in the above manner.
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The user would not need to decipher difficult to understand data
entry screens.
However, having an identity automatically provided, including its
password, does have some particular usability issues. Users are used
to having to provide their username and password to access remote
services. When attempting to access services, authenticating to them
completely transparently to the user could represent a source of
confusion. User training within an organisation to explain that
automated population of their identity has been enabled is the only
way to counter this.
6.5. Modifying Identity Information
This process is conceptually fairly similar to adding an identity,
and thus shares many of the usability issues with that process. Some
particular things are discussed here.
6.5.1. Manual Modification
An identity selector may allow a user to manually modify some or all
of the information associated with each identity. The obvious items
that SHOULD be allowed to be changed by the user are the friendly
name, the friendly icon, and the credential, or password, associated
with the identity.
The identity selector should restrict other modification of the
information:
o Identity Selectors SHOULD NOT allow the editing of the NAI of an
identity or the trust anchor of an identity provider for items
that have been added through automated means (Section 6.4.1.2,
Section 6.4.1.3, Section 6.4.2.2 and Section 6.4.2.3).
o Identity Selectors MAY allow the update of the trust anchor of
identity providers that have stored the trust anchor through just
in time manual addition, using another just in time retrieval of
the trust anchor. Any identity selector that allows this update
MUST inform the user of the change in the trust anchor, and advise
the user that any unexpected change should be assumed to be an
attack.
o Identity Selectors SHOULD NOT allow manual modification of the
password changing URL.
o Identity Selectors SHOULD NOT allow manual modification of the
helpdesk URL.
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6.5.2. Automated Modification
To ease usability, organisations may wish to automatically provide
updates to identity provider or identity information. For example,
if the user's password changes it could automatically update the
password for the identity in the user's identity selector, or if the
trust anchor information changes (e.g. if a certificate is changed)
it could be automatically pushed out to all users.
6.6. Verifying an identity
An inherent by-product of the ABFAB architecture is that an identity
cannot be verified during the addition process; it can only be
verified while it is in use with a real service. This represents a
definite usability issue no matter which method of identity addition
is used (see Section 6.4):
o If the user has manually added the identity (see Section 6.4) they
may have gone through the whole manual process with no errors and
so believe the identity has been set up correctly. However, when
they attempt to access a service, they may be given an error
message, thus causing some amount of confusion.
o If the user has had the identity populated into their identity
selector, then there is a much greater chance of the identity
information being correct. However, if any of the information is
not correct, then there is the potential for confusion as the user
did not add the information in the first place.
Also, if the identity information is incorrect the user may not know
where the error lies, and the error messages provided by the process
may not be helpful enough to indicate the error and how to fix it
(see Section 8).
6.7. Removing an Identity
This is fairly similar to adding or modifying an identity, and thus
shares many of the usability issues with those processes. Some
particular things are discussed here.
6.7.1. Manual Removal
Allowing the user to manually delete an identity is probably the best
way to achieve the goal. Any UI should allow for this option.
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6.7.2. Automated Removal
While automated removal of an identity is a way of achieving the goal
without having to interact with the user, the consequence is that
things may disappear from the user's identity selector without them
realising.
6.8. Storing an Identity with or without credentials
Sometimes, a user may wish to have the identity they wish to use with
a service stored by the identity selector, but not the credential
(e.g. password) that goes along with that Identity. The consequence
of this is that when a user attempts to authenticate to a service for
which an identity, but no credential, is stored, then the user would
need to be prompted to manually enter the credential.
7. Considerations around Management of Service to Identity Mappings
A service to identity mapping tells the identity selector which
identity should be used for a particular service. There is
potentially a many-to-many association between identities and
services since a user may wish to use one of their identities for
many services, or more than one identity for a single service (e.g.
if they have multiple roles on that service).
This potentially complex many-to-many association between identities
and services is not easily comprehended by the user, and allowing the
user to both manipulate it and control can be challenging. These
obstacles are especially common when errors occur after an
association has been made. In this scenario it is important that an
identity can be disassociated with a service.
To further complicate the picture, users may wish for:
1. The identity to service mapping to be stored along with the
credential, i.e. the user should always be authenticated to a
particular service with a particular identity with no prompting.
2. The identity to service mapping to be stored but not the
credential, i.e. the user should not be prompted to choose the
identity for a particular service, but should be prompted to
enter their credential for that identity.
3. The identity to service mapping to not be stored, i.e. the user
should be asked which identity to use every time they
authenticate to a particular service.
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7.1. Associating a Service with an Identity
There needs to be a way for the user to create the service to
identity association. It is advisable that this link be made only
after the identity in question has authenticated with the service
without any error.
There are a few ways this association could happen.
7.1.1. User-driven Manual Association
There are two ways in which manual association of an identity to a
service could happen:
1. The identity selector MAY allow the user to associate a
particular service with a particular identity manually, using the
identity selector before they first attempt to use the service.
This method is inadvisable, however, because not only might the
identity in question not yet have authenticated successfully, the
user would also need to know all the required technical details
of that service beforehand, such as its GSS Acceptor Name.
2. On encountering a service new to the identity selector, the
identity selector SHOULD pop up a dialogue box to the user asking
if they would like to use an existing identity for this service
(and might also allow them to create a new identity and use
that).
7.1.2. Automated Rules-based Association
It would be beneficial from a usability perspective to minimise - or
avoid entirely - situations where the user has to pick an identity
for a particular service. This could be accomplished by having rules
to describe services and their mapping to identities. Such a rule
could match, for example, a particular identity for all IMAP servers,
or a particular identity for all services in a given service realm.
These rules could be configured as a part of the automated identity
addition process described in Section 6.4.2.2 or Section 6.4.2.3.
7.1.3. Association Conflicts
The presence of rules-based associations brings with it potential
conflicts in the rules. A non-exhaustive list of conflicts includes:
o One rule applies to all services of a particular type, while
another rule applies to all services within a particular domain.
For example, one rule applies identity A to all IMAP services,
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while another rule applies identity B to all services in the
example.com domain.
o One rule originates from enterprise management tools as described
in Section 6.4.2.3, and another rule originates from manual
addition.
o The user has associated an identity with a service upon
encountering the service for the first time, and later creates a
rule that matches all services within that service's realm.
Identity selectors MUST order the precedence of rules as follows:
1. Manually created rules matching specific services and realms
2. Enterprise created rules matching specific services and realms
3. Manually created rules matching any service in a single realm
4. Enterprise created rules matching any service in a single realm
5. Manually created rules matching a single service in any realm
6. Enterprise created rules matching a single service in any realm
Identity selectors SHOULD notify the user whenever a new rule will
take precedence over an existing rule.
7.2. Disassociating a Service with an Identity
A user MUST be able to disassociate an identity with a service - that
is, to be able to remove the mapping without having to remove the
identity.
For serious authentication errors, the identity selector SHOULD
prompt the user to choose whether to disassociate the identity from
the service or retain the association. The prompt SHOULD explain the
nature of the error.
When such a serious authentication error occurs and the identity is
selected by a rules-based association (Section 7.1.2), any
disassociation prompt MUST inform the user that the identity was
selected by a rule. The prompt SHOULD allow the user to retain the
association, or to disassociate the rule altogether. The prompt MAY
include a third choice, to create an exception so that the rule does
not apply to this specific service.
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As of this writing, there are no authentication failures that should
cause the disassociation of an identity from a service.
7.3. Listing Services and Identities
A service listing should be considered in the identity selector which
is both searchable and editable by the user.
7.4. Showing the Service that is requesting Authentication
When a user is attempting to authenticate to a service for the first
time, there should be some indication given to the user as to which
service is requesting authentication. In many cases, the service may
be obvious (where the user has started the process of attempting to
authenticate to a particular service), but in other cases this may
not be obvious (e.g. if an authentication attempt is triggered by a
timer or a specific event), and for this scenario some indication as
to the requesting service is necessary.
7.5. Showing the Identity currently in use
It would be beneficial if, when using a service, the identity
currently in use could be made visible to the user while they are
using a specific service. This allows the user to identify which
identity is used with a particular service at a particular time (the
user may have more than one identity that they could use with a
particular service) - so that they can then disassociate the pairing.
This is especially useful when the identity is selected without any
user prompt, because of a previous association.
Implementing such a feature may be hard, however, due to the layered
nature of the ABFAB transaction - the identity selector will
certainly know when successful (or failed) authentications to a
particular service have happened, but after that it typically plays
no further part in the use of the service. Therefore, knowing that a
particular service is still using a particular identity in order to
indicate this to the user would be challenging.
One approach that could be used would be to display OS notifications
when an identity is used. The notification could include information
such as the application requesting the identity, the service
receiving the identity, and the identity used. Another approach
could be for the identity selector to maintain a history of identity
use.
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7.6. Multiple Identities for a Particular Service
An Identity Selector should be able to deal with the case where a
user has multiple identities associated with a single service. For
example, upon receiving a request for authentication to a service
that multiple identities are configured for, ask the user which of
the identities should be used in this instance.
7.7. Not using ABFAB for a Particular Service
There may be cases where a user does not wish to use ABFAB based
authentication at all to a particular service, even though it is
ABFAB enabled. To support this, the identity selector would have to
allow the user to choose not to use ABFAB when they attempt to
authenticate to a service. It would be desirable if the user could
also flag that this should be remembered.
8. Handling of Errors
Errors during the ABFAB authentication process can happen at any of
the many layers - they could be GSS-API errors, EAP errors, RADIUS/
RadSec errors, SAML errors, application errors, etc. ABFAB based
technologies are limited in error handling by the limitations in the
protocols used.
8.1. Errors in GSS-API
All GSS-API calls are necessarily instantiated from within the
calling application. For this reason, when an error occurs the error
is passed back to the application in order for it to deal with it.
To retry, the application needs to re-initiate the GSS-API call.
Unless the application has been written to deal with this properly,
this process can be very tedious for a user and cause them opt out of
what they are trying to accomplish. In addition to this, the
application may not display the error messages to the user. Even
when the application does display the errors, the messages themselves
may not be useful enough for the user to decipher what has gone
wrong.
Two extensions to GSS-API are suggested for the consideration of the
kitten working group:
o GSS-API should provide a method for applications to invoke to
indicate that the application has displayed the last error to the
user.
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o GSS-API should provide a method for applications to invoke to
indicate that the authentication succeeded, but is insufficient
for the task at hand and needs to be retried.
8.1.1. Log of Errors
The Identity Selector can improve the general GSS-API error reporting
experience by displaying a list of errors experienced by ABFAB
applications. When an application error occurs, the EAP mechanism
MAY record that error. If the mechanism records these errors, the
Identity Selector MAY display these errors to the user. Thus, the
user will have a single place to go to view all of the errors that a
user experiences across all applications. Therefore, an Identity
Selector that implements an error display SHOULD present the user
with the context of the error, including the calling application and
the time.
8.2. Examples of errors
To give an idea of the range of errors that might be seen, consider
the following non-exhaustive set of potential errors.
Identity Association/Verification Errors:
o The credentials presented to the IdP were not able to be verified
- e.g. wrong username/password.
o The Trust Anchor for the IdP was invalid.
Service Errors:
o The IdP recognizes the client, but decides not to authorize it for
this service.
o The EAP session succeeds, but the RADIUS system sends access-
reject to the Relying Party
o The RADIUS system succeeds, but the Relying Party rejects the
session. For instance, the SAML part of the session could contain
an error that causes the Relying Party to reject the client.
o The Identity might have been successfully authenticated, but the
user might not have authorisation to use the service or privilege
levels within the service they are attempting to use. For
instance, the Identity could authorise the use of an operating
system as an unprivileged user, which would prevent the user's
goal of managing the hard drives.
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Other Errors:
o The IdP didn't respond to the Service.
o The IdP didn't respond to the Client.
o Network errors.
o Timing errors.
9. Handling of Successes
It is of course hoped that the identity selector will have to
occasionally handle successes as well as errors. This section has
some brief discussion about some areas you might want to think about.
9.1. Reporting Authentication Success on First Use of Identity
The first time an identity is used with a service, it would be good
practice to visually indicate in some way that the process has been
successful, in order that the user understands what is happening and
is then prepared for future authentication attempts.
9.2. Reporting Authentication Success
On an on-going basis you may or may not wish to indicate visually to
the user a successful authentication to a service. This relates to
Section 7.5.
10. Other Considerations
This section briefly discusses other considerations that you might
want to think about that don't fit in any of the other categories.
10.1. Identity Selector Taking Focus
When an ABFAB authentication request is triggered, and where it needs
input from the user, the Identity Selector should take focus in some
way so that it is clear to the user that they need to do something to
proceed.
10.2. Import/Export of Credentials
For various reasons, an identity selector implementation might want
to include functionality that allows for the export/import of
identities and service to identity mappings. This could be for
backup purposes, to allow a degree of mobility between identity
selector instances, etc.
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If providing this functionality, it would be advisable that the
credential store that is the result of the export should be secure -
encrypted and password protected - given the nature of the
information.
11. Security Considerations
Most security considerations are ones relevant to the use of GSS-EAP
and are detailed in [I-D.ietf-abfab-arch]. There are, however, a few
specific sets of security considerations related to the UI
implementation.
First, as discussed earlier, the Identity Selector should use a Trust
Anchor to authenticate the IdP before it sends the users credentials
to it. Having no Trust Anchor information at all, or an incorrect
Trust Anchor, can enable the possibility of someone spoofing the IdP
and harvesting credentials sent to it. So, how this Trust Anchor is
configured and managed can have major security implications:
o The most secure way for a Trust Anchor to be configured is to have
it provisioned alongside the other identity information in an
enterprise provisioning scenario. This allows for the correct
Trust Anchor to be configured with no user input required.
However, thought needs to be given to Trust Anchor expiry and
consequent requirement for regular reprovisioning of identity
information.
o Another way that is potentially secure would be to allow the user
to discover the Trust Anchor information out of band and manually
input this information into the Identity Selector. This is only
secure, however, for those users who understand what they're doing
in this scenario; pragmatically, this is unlikely to be the case
for many users so is not a recommended approach for the average
user.
o A pragmatic approach would be leap of faith, whereby no Trust
Anchor information is initially provisioned, and the first time
the Identity Selector connects to the IdP it remembers the Trust
Anchor information for future use. This doesn't mitigate against
spoofing of an IdP in the first instance, but would enable
mitigation against it for all future connections.
o Finally, there may be interesting ways to leverage technologies
such as DANE [RFC6698] to store the Trust Anchor for an IdP in
DNS.
Secondly, the storage of the user's credentials by the Identity
Selector should be done in a secure manner to mitigate against people
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taking unauthorised control of the device being able to gather these
credentials. Use of a secure credential storage mechanism, such as
the GNOME Keyring on Linux, or Keychain on the Mac, are recommended.
12. Privacy Considerations
Since the ABFAB system facilitates the sharing of identifying
information about a user, the undesired sharing of information is a
real concern. Most of the privacy considerations lie outside the
scope of the Identity Selector UI, which neither controls nor sees
which attributes of an identity will be shared with a service. In
essence, the only control that the Identity Selector has is whether
or not a given identity will be shared with the service.
However, the selection of identity does warrant privacy
considerations. Any automated choice of identity for a service will
share information, potentially inappropriately. Examples of this
include:
o Rules that apply to a service across all realms will cause an
identity choice, even for realms the user would actually prefer to
avoid interacting with at all.
o Storing a default for a particular service and realm will cause
the identity to be selected in that situation going forward, even
if the situation or application does not warrant that. For
instance, a web browser in privacy mode ideally should not know of
any saved identity association choices.
Even appropriate choices of sharing an identity with a service leaks
information about the user. The desired service and the identity
provider must communicate with each other to perform an
authentication. Even if the authentication fails, the service will
know the realm of the user credential, and the Identity Provider will
know the realm, and maybe the service, that the user tried to access.
For services with fallback authentication mechanisms, the system may
try and fail to authenticate the user, thus sharing the realm
information noted above, without the user being aware this has
happened.
13. IANA Considerations
This document does not require actions by IANA.
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14. Contributors
The following individuals made important contributions to the text of
this document: Sam Hartman (Painless Security LLC), and Maria Turk
(Codethink Ltd).
15. Acknowledgements
Thanks to Jim Schaad, Stefan Winter, David Chadwick, Kevin Wasserman,
Alejandro Perez-Mendez, Ken Klingenstein, and Dave Crocker for
feedback and suggestions.
16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The
Network Access Identifier", RFC 4282,
DOI 10.17487/RFC4282, December 2005,
<http://www.rfc-editor.org/info/rfc4282>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <http://www.rfc-editor.org/info/rfc6698>.
[I-D.ietf-abfab-arch]
Howlett, J., Hartman, S., Tschofenig, H., Lear, E., and J.
Schaad, "Application Bridging for Federated Access Beyond
Web (ABFAB) Architecture", draft-ietf-abfab-arch-12 (work
in progress), February 2014.
[I-D.ietf-abfab-usecases]
Smith, R., "Application Bridging for Federated Access
Beyond web (ABFAB) Use Cases", draft-ietf-abfab-
usecases-05 (work in progress), September 2012.
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16.2. Informative References
[MS-CS] Brown, K., "The InfoCard Identity Revolution", July 2006,
<https://technet.microsoft.com/en-us/
magazine/2006.07.infocard.aspx>.
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Appendix A. Change Log
Note to RFC Editor: if this document does not obsolete an existing
RFC, please remove this appendix before publication as an RFC.
IETF draft -03 to ietf draft -04
1. Document service errors.
2. Document GSS error handling, including a request for a couple of
new GSS methods, and maintaining a log of all GSS errors for
later viewing.
IETF draft -02 to ietf draft -03
1. Tidying up language throughout.
2. Added the idea of an identity provider object within the identity
selector, and moved the trust anchor property from the identity
to the identity provider.
3. Added restrictions on manual modification of automatically added
identities and identity providers.
4. Added precedence between identity association rules.
5. Incorporated many comments from the mailing list.
6. Added privacy considerations section.
IETF draft -01 to ietf draft -02
1. Tidying up language throughout.
2. Finished remaining TODOs - largely in the error handling section.
3. Added security considerations section.
IETF draft -00 to ietf draft -01
1. Tidying up language throughout
2. Doing some of the TODOs
3. Added language that tries to explain that this document is not a
substitute for good HCI/UX design.
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4. Changed terminology slightly to avoid confusion between an
identity selector "mechanism" and a GSS-API mechanism.
5. Added a caveat about the potential for the UI to show the
identity currently in use for a particular service.
6. Added a requirement that the identity selector must not store the
same NAI for multiple identities.
7. Stopped talking about "provisioning" after saying that I wouldn't
talk about "provisioning".
Draft -04 to ietf draft -00
1. Adding brief discussion of identities vs identifiers (Ken).
2. Changing assumption about credentials having a password in favour
of more generic text for other auth types.
3. Adding discussion of storage of identity information.
4. Added sections on dealing with multiple identities per service,
remembering credentials, remembering not to use ABFAB.
5. Added small section on ID selector needing to take focus in some
way.
Draft -03 to draft -04
1. Addressing various comments from Jim and Stefan.
Draft -02 to draft -03
1. Bumping version to keep it alive.
Draft -01 to draft -02
1. Completed the major consideration sections, lots of rewording
throughout.
Draft -00 to draft -01
1. None, republishing to refresh the document. Other than adding
this comment...
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Appendix B. Open Issues
Note to RFC Editor: please remove this appendix before publication as
an RFC.
Authors' Addresses
Dr. Rhys Smith
Cardiff University
39-41 Park Place
Cardiff CF10 3BB
United Kingdom
Phone: +44 29 2087 0126
EMail: smith@cardiff.ac.uk
Mark Donnelly
Painless Security
14 Summer Street
Suite 202
Malden, Massachusetts 02176
United States
EMail: mark@painless-security.com
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