Open Stack

On Mon, Sep 24, 2018, at 4:16 PM, Lance Bragstad wrote:
> On Mon, Sep 24, 2018 at 7:00 AM Colleen Murphy <colleen at gazlene.net> wrote:
> 
> > This is in regard to https://launchpad.net/bugs/1641625 and the proposed
> > patch https://review.openstack.org/588211 for it. Thanks Vishakha for
> > getting the ball rolling.
> >
> > tl;dr: Keystone as an IdP should support sending
> > non-strings/lists-of-strings as user attribute values, specifically lists
> > of keystone groups, here's how that might happen.
> >
> > Problem statement:
> >
> > When keystone is set up as a service provider with an external
> > non-keystone identity provider, it is common to configure the mapping rules
> > to accept a list of group names from the IdP and map them to some property
> > of a local keystone user, usually also a keystone group name. When keystone
> > acts as the IdP, it's not currently possible to send a group name as a user
> > property in the assertion. There are a few problems:
> >
> >     1. We haven't added any openstack_groups key in the creation of the
> > SAML assertion (
> > http://git.openstack.org/cgit/openstack/keystone/tree/keystone/federation/idp.py?h=14.0.0#n164
> > ).
> >     2. If we did, this would not be enough. Unlike other IdPs, in keystone
> > there can be multiple groups with the same name, namespaced by domain. So
> > it's not enough for the SAML AttributeStatement to contain a
> > semi-colon-separated list of group names, since a user could theoretically
> > be a member of two or more groups with the same name.
> >    * Why can't we just send group IDs, which are unique? Because two
> > different keystones are not going to have independent groups with the same
> > UUID, so we cannot possibly map an ID of a group from keystone A to the ID
> > of a different group in keystone B. We could map the ID of the group in in
> > A to the name of a group in B but then operators need to create groups with
> > UUIDs as names which is a little awkward for both the operator and the user
> > who now is a member of groups with nondescriptive names.
> >     3. If we then were able to encode a complex type like a group dict in
> > a SAML assertion, we'd have to deal with it on the service provider side by
> > being able to parse such an environment variable from the Apache headers.
> >     4. The current mapping rules engine uses basic python string
> > formatting to translate remote key-value pairs to local rules. We would
> > need to change the mapping API to work with values more complex than
> > strings and lists of strings.
> >
> > Possible solution:
> >
> > Vishakha's patch (https://review.openstack.org/588211) starts to solve
> > (1) but it doesn't go far enough to solve (2-4). What we talked about at
> > the PTG was:
> >
> >     2. Encode the group+domain as a string, for example by using the dict
> > string repr or a string representation of some custom XML and maybe base64
> > encoding it.
> >         * It's not totally clear whether the AttributeValue class of the
> > pysaml2 library supports any data types outside of the xmlns:xs namespace
> > or whether nested XML is an option, so encoding the whole thing as an
> > xs:string seems like the simplest solution.
> >
> 
> Encoding this makes sense. We can formally support different SAML data
> types in the future if a better solution comes along. We would have to make
> the service provider deal with both types of encoding, but we could
> eventually consolidate, and users shouldn't know the difference. Right?

The only way this would make a difference to the user is if they need to debug a request by actually looking at the response to this request[1]. If we were to base64-encode the string that immediately obfuscates what the actual value is. I'm not really sure if we need to base64-encode it or just serialize it some other way.

[1] https://developer.openstack.org/api-ref/identity/v3-ext/index.html#id404
> 
> 
> >     3. The SP will have to be aware that openstack_groups is a special key
> > that needs the encoding reversed.
> >         * I wrote down "MultiDict" in my notes but I don't recall exactly
> > what format the environment variable would take that would make a MultiDict
> > make sense here, in any case I think encoding the whole thing as a string
> > eliminates the need for this.
> >     4. We didn't talk about the mapping API, but here's what I think. If
> > we were just talking about group names, the mapping API today would work
> > like this (slight oversimplification for brevity):
> >
> > Given a list of openstack_groups like ["A", "B", "C"], it would work like
> > this:
> >
> > [
> >   {
> >     "local":
> >     [
> >       {
> >         "group":
> >         {
> >           "name": "{0}",
> >           "domain":
> >           {
> >             "name": "federated_domain"
> >           }
> >         }
> >       }
> >     ], "remote":
> >     [
> >       {
> >         "type": "openstack_groups"
> >       }
> >     ]
> >   }
> > ]
> > (paste in case the spacing makes this unreadable:
> > http://paste.openstack.org/show/730623/ )
> >
> > But now, we no longer have a list of strings but something more like
> > [{"name": "A", "domain_name": "Default"} {"name": "B", "domain_name":
> > "Default", "name": "A", "domain_name": "domainB"}]. Since {0} isn't a
> > string, this example doesn't really work. Instead, let's assume that in
> > step (3) we converted the decoded AttributeValue text to an object. Then
> > the mapping could look more like this:
> >
> > [
> >   {
> >     "local":
> >     [
> >       {
> >         "group":
> >         {
> >           "name": "{0.name}",
> >           "domain":
> >           {
> >             "name": "{0.domain_name}"
> >           }
> >         }
> >       }
> >     ], "remote":
> >     [
> >       {
> >         "type": "openstack_groups"
> >       }
> >     ]
> >   }
> > ]
> > (paste: http://paste.openstack.org/show/730622/ )
> >
> >
> I can't come up with a reason not to do this at the moment. If we serialize
> the group+domain name information in SAML, then it seems appropriate to
> teach the service provider how to deserialize it and apply it to mappings.
> Otherwise, does it make sense to build serialization into the identity
> provider if we aren't going to use the domain name?
> 
> 
> > Alternatively, we could forget about the namespacing problem and simply
> > say we only pass group names in the assertion, and if you have ambiguous
> > group names you're on your own. We could also try to support both, e.g.
> > have an openstack_groups mean a list of group names for simpler use cases,
> > and openstack_groups_unique mean the list of encoded group+domain strings
> > for advanced use cases.
> >
> > Finally, whatever we decide for groups we should also apply to
> > openstack_roles which currently only supports global roles and not
> > domain-specific roles.
> >
> > (It's also worth noting, for clarity, that the samlize function does
> > handle namespaced projects, but this is because it's retrieving the project
> > from the token and therefore there is only ever one project and one project
> > domain so there is no ambiguity.)
> >
> > Thoughts?
> >
> > - Colleen (cmurphy)
> >
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