[openstack-dev] [Keystone] Federated Identity Management and user creation

David Chadwick d.w.chadwick at kent.ac.uk
Thu Jan 31 22:08:41 UTC 2013

On 31/01/2013 18:33, Adam Young wrote:
> On 01/31/2013 10:40 AM, David Chadwick wrote:
>> this is missing the whole point of federation and ABAC. We do not want
>> to base access on unique IDs (or the lack of them) but rather on the
>> identity attributes that users posses. Your proposal would only work
>> if all users from the same IDP had the same set of identity
>> attributes. But this is obviously not the case.
> Nope.
No sure what the nope was to.

> WHat matters is what is in the token.  The User ID is just a
> book-keeping tool in this case.

Agreed. It is clear that what matters to the CSP is what is in the token 
(if it validates the token) or what Keystone says is in the token (if it 
asks Keystone to validate it), and not what Keystone stores in its 
databases, since the CSP does not access the databases.

In order for the token system to work, Keystone does not need a 
persistent entry in its user database. It only needs a transient entry 
which can be deleted after the user's session has completed. The book 
keeping can cease once the user has finished using the CSP. The audit 
trail remains in perpetuity, even if the user's account in Keystone has 
been deleted.

>> As I said in a previous posting, a new way of thinking about authz is
>> needed, one that is not based on the unique user IDs that Keystone
>> assigns.
> Think of it his way.  If i invite you to the Open Stack table via
> Federation, I am responsible for you.

By "I" I assume you mean the OpenStack/Keystone administrator, so I 
agree with this. However, in a federated system, the OpenStack/Keystone 
administrator trusts the federation IDPs to administer the user 
accounts, databases and user authentication tokens, so that he does not 
have to. This is the whole point of federation. In a federation, the SP 
trusts the IDP to manage the user accounts so that it does not have to. 
Which is actually what OpenStack currently supports in that the CSPs 
trust Keystone to do the user account management. We are simply 
extending the existing trust model into a federated environment so that 
the CSP trusts Keystone and Keystone trusts the federated IDPs. Thus 
there is no point in replicating the users accounts in Keystone since 
they already exist and are managed by the trusted IDPs.

  The common userID is the account
> responsible for the actions of the ephemeral users.

I simply dont see why you need this, or how it will help to authorise 
users. In fact it will mess up the authz if the CSP uses the userID in 
its access control lists, because in this case all users would have the 
same access rights, which is not what is required.

> The token will have a set of identity attributes in it, signed by
> Keystone.

Actually it should have the mapped attributes in it, the ones that the 
CSP knows and uses for authorising the users (especially if the CSP is 
going to validate the token. There is no point in putting strange IDP / 
organisational attributes in the token).

  That is all the user needs, not a separate account in
> Keystone's user table.

At last we agree on this. The user does not need a duplicate account in 

> Another way of saying it is that we already have an ephemeral user
> construct, it is the token.


>> For a start, when you first configure your federated OpenStack system,
>> there wont be any users in the database and so there wont be any
>> unique Keystone user IDs, so services wont be able to create ACLs
>> based on them.
> Not true.  There are mechanisms for pre-populateing the users, part of
> the install system.  You don't need to completely pull yourself up by
> your own bootstraps.

But this is for the non-federated environment where users have to be in 
the keystone database in order to authenticate and get tokens.

In the federated world the users account is already in the IDP's 
database (as is his pw).



>> However, the users *do* exist, and they do have identity attributes
>> that will be asserted by the IDPs. So the services *can* build their
>> access controls at initialisation time, before any users are created
>> in Keystone (I am only taking about end users not admin users which
>> will exist). The services do this by deciding which keystone
>> attributes (project, roles etc) they will give the users in exchange
>> for their IDP asserted attributes via the new attribute mapping
>> service we have built.
>> So when a user does log in, via his IDP, a temporary user entry in
>> Keystone is created for the session, his IDP attributes are mapped
>> into the correct set of roles and projects (tenants), and the service
>> gives the user the correct set of access rights. When the session is
>> completed, the user entry will be automatically deleted from Keystone.
>> Its clean and simple. Kristy is already building this
>> regards
>> David
>> On 31/01/2013 15:29, Adam Young wrote:
>>> Create a user per federated source. Federated users with no unique IDs
>>> are associated with the common user account.  That account should be
>>> able to access the set of all resources that anyone in the account can
>>> have.  It should not have a password, and users should not be able to
>>> log in as that Federated user account.
>>> On 01/29/2013 07:41 AM, David Chadwick wrote:
>>>> Hi Adam
>>>> I have addressed auditability in my previous post. Misuse can still be
>>>> addressed even with transient IDs and transient users, so no further
>>>> comments here on that issue.
>>>> In our initial implementation of FIM we did indeed create new users in
>>>> Keystone for every new user arriving from an IDP. This has two
>>>> negative consequences
>>>> a) we cannot deal with users with transient IDs (as can be produced by
>>>> Shibboleth) so we have to mandate that permanent IDs are used by all
>>>> IDPs (which Shibboleth can do). Still its a (minor) limitation.
>>>> b) we have a housekeeping problem of knowing when to delete old users
>>>> from the user database. In our initial implementation we did not
>>>> address this, so the database just keeps on growing unless manual
>>>> intervention takes place. This is a tricky problem to solve. When
>>>> should an entry be deleted? Time limits is not an adequate solution.
>>>> My account at Kent has been active for 8 years and growing, whereas
>>>> students accounts are deleted each year. Should the IDP notify
>>>> Keystone every time its database is updated? Or something else?
>>>> So we thought that a better option would be to only hold transient
>>>> user entries in Keystone for the duration of the validity time of the
>>>> identity assertion from the IdP. This solves the user management
>>>> problem, as well as the rights revocation problem, since a user now
>>>> only has rights for the duration of his session. (If you want active
>>>> revocation in the middle of a session this is a different issue.) User
>>>> management is pushed right back to the IDP, which is the right place
>>>> for it. The IDP keeps its user database up to date, and only current
>>>> users will be given credentials to access Keystone.
>>>> As far as I can tell the only negative consequence is on a service
>>>> which currently uses the user ID in its access control list. Since
>>>> Keystone creates this ID automatically when a user entry is created,
>>>> then the same user will have different ID for different sessions. So
>>>> the user ID ACL system wont work without either
>>>> a) Federated Keystone having a different way of assigning unique IDs
>>>> to user entries, so that the IDs can be the same for the same user
>>>> even if the entry is deleted then created again, or
>>>> b) services using a different attribute type in their ACLs (one that
>>>> still contains a permanent unique ID for the user).
>>>> regards
>>>> David
>>>> On 28/01/2013 17:50, Adam Young wrote:
>>>>> On 01/28/2013 08:20 AM, K.W.S.Siu wrote:
>>>>>> Hello,
>>>>>> When Federated Identity Management is used, the authentication
>>>>>> statement issued by the external Identity Provider(s) may contain a
>>>>>> temporary (or transient) identifier for the user rather than a
>>>>>> permanent (or persistent) one. Because of this, it is not possible to
>>>>>> always uniquely identify the user each time when federated
>>>>>> authentication is used in Keystone (unless one of the user's identity
>>>>>> attributes is globally unique, such as an email address). As an
>>>>>> existing user is required to issue tokens, it is necessary to
>>>>>> create a
>>>>>> new user each time authentication takes place which could result in
>>>>>> the backend storage becoming full of redundant data. As a solution to
>>>>>> this, we propose the addition of a validity time field in the user
>>>>>> entity which can be used to remove expired user data and allow
>>>>>> temporary users to be created based on the ID provided by the
>>>>>> Identity
>>>>>> Provider. Determining the details of the new user account will be
>>>>>> done
>>>>>> by the proposed attribute mapping service.
>>>>> That is a pretty important distinction.  It would potentially have
>>>>> impacts on Auditability.  Once you say the user object is
>>>>> transient, it
>>>>> n longer has an authority to address misuse, at which point it falls
>>>>> back on the organization that is Federated to Keystone. Would it be a
>>>>> cleaner solution to link the tokens with a single federated
>>>>> account, and
>>>>> then to use that account to create all tokens?  The tokens could
>>>>> have a
>>>>> subset of roles and access to a subset of endpoints based on the data
>>>>> approved by the Federated organization.  It would just be a metter of
>>>>> nailing down how the ephemera ids are issued.  I would almost want
>>>>> them
>>>>> to be stored in a separate table from the users, which is what the
>>>>> token
>>>>> table already is.
>>>>> Is it essential that we modify the user object, or are you just
>>>>> proposing it as a "path of least resistance?"
>>>>>> At the moment we are wondering how people feel about this, and if
>>>>>> anyone has any comments or suggestions.
>>>>>> Many thanks,
>>>>>> Kristy
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