In Ipsilon, we recently (OK, about a year ago) added an authorisation stack. This allows us to control, Ipsilon-side, which users are permitted to log into which service providers. Our authorisation plugin functions are currently fairly limited, basically using user group membership to control which service providers a user has access to. One of the things we'd like to support is using FreeIPA's HBAC rules rather than user attributes directly. In my opinion, this makes it much more obvious what's going on and fits in better with FreeIPA's architecture.
There're a few options that have come up in discussions around this on #ipsilon and #sssd:
1) Treat each service provider as a new service in FreeIPA. The most basic HBAC rule would then be "<user> can log into <ipsilon server> via service <service provider>". Ipsilon can easily do a PAM_ACCT_MGMT PAM call (either using a PAM library, or by talking to SSSD directly using the PAM socket) with the appropriate service name. SSSD will then permit or deny the check based on the HBAC rules. This is nice and simple, but the permitted length / characters of service names could have a potential limit on what service providers can be authorised this way.
2) Ipsilon fetches HBAC rules from FreeIPA and processes them itself. This requires duplication of the HBAC processing logic in Ipsilon (although I believe the python bindings for libipa_hbac deal with most of the heavy lifting there), and LDAP connectivity to the FreeIPA server(s), along with the appropriate login credentials. Ipsilon would need to have any appropriate retry / failover logic. With this method, we can create service providers as hosts in FreeIPA, and HBAC rules would be "<user> can log into <service provider> via service saml2" (or openidc, etc).
3) Ipsilon uses the FreeIPA JSON-RPC API to call the hbactest API. This moves the HBAC check to the FreeIPA server, where the logic already exists. This requires Ipsilon to have access to the FreeIPA API and the appropriate login credentials. Moving the HBAC checks into FreeIPA itself has load implications for the IPA servers. Again, this would permit HBAC rules of the style "<user> can log into <service provider> via saml2".
4) Add support to SSSD for performing HBAC checks for arbitrary FreeIPA hosts. This lets SSSD deal with connections to FreeIPA, including authentication and failover, which it's already doing. Some mechanism would be needed for Ipsilon to pass the "destination host" to SSSD for use in the HBAC check rather than the local IPA hostname.
All of these options assume that there's an HBAC rule to permit the user to log in to the Ipsilon server itself via the "ipsilon" service, which we require now.
Considering I'm writing this mail, it'll come as no surprise that I'm most interested in option 4. SSSD only fetches HBAC rules from FreeIPA that affect the local host (unless the legacy src host option is enabled), so there'd need to be an option to enable fetching all rules instead. I'm not clear if there's a PAM attribute that could be used to pass the remote host name to SSSD for the check, so my thought was to add HBAC functionality to the infopipe (Ipsilon can already use the Infopipe for fetching user attributes). My first thought is something like an org.freedesktop.sssd.infopipe.HBAC DBus interface with an Evaluate method that takes hostname, username, and service name, and returns a boolean.
So, basically, if I were to work up patches to implement this option, would they have a chance of being accepted into SSSD? In the meantime we'll probably look at implementing one of option 2 or 3, but the SSSD option is appealing to me in the longer term.
Cheers.
On Tue, Jun 27, 2017 at 11:40:37AM +0100, Howard Johnson wrote:
In Ipsilon, we recently (OK, about a year ago) added an authorisation stack. This allows us to control, Ipsilon-side, which users are permitted to log into which service providers. Our authorisation plugin functions are currently fairly limited, basically using user group membership to control which service providers a user has access to. One of the things we'd like to support is using FreeIPA's HBAC rules rather than user attributes directly. In my opinion, this makes it much more obvious what's going on and fits in better with FreeIPA's architecture.
There're a few options that have come up in discussions around this on #ipsilon and #sssd:
- Treat each service provider as a new service in FreeIPA. The most basic
HBAC rule would then be "<user> can log into <ipsilon server> via service <service provider>". Ipsilon can easily do a PAM_ACCT_MGMT PAM call (either using a PAM library, or by talking to SSSD directly using the PAM socket) with the appropriate service name. SSSD will then permit or deny the check based on the HBAC rules. This is nice and simple, but the permitted length / characters of service names could have a potential limit on what service providers can be authorised this way.
- Ipsilon fetches HBAC rules from FreeIPA and processes them itself. This
requires duplication of the HBAC processing logic in Ipsilon (although I believe the python bindings for libipa_hbac deal with most of the heavy lifting there)
correct. I think this would be the second-quickest path forward.
, and LDAP connectivity to the FreeIPA server(s), along with the appropriate login credentials. Ipsilon would need to have any appropriate retry / failover logic. With this method, we can create service providers as hosts in FreeIPA, and HBAC rules would be "<user> can log into <service provider> via service saml2" (or openidc, etc).
- Ipsilon uses the FreeIPA JSON-RPC API to call the hbactest API. This
moves the HBAC check to the FreeIPA server, where the logic already exists. This requires Ipsilon to have access to the FreeIPA API and the appropriate login credentials. Moving the HBAC checks into FreeIPA itself has load implications for the IPA servers. Again, this would permit HBAC rules of the style "<user> can log into <service provider> via saml2".
I think this is the quickest path forward.
- Add support to SSSD for performing HBAC checks for arbitrary FreeIPA
hosts. This lets SSSD deal with connections to FreeIPA, including authentication and failover, which it's already doing. Some mechanism would be needed for Ipsilon to pass the "destination host" to SSSD for use in the HBAC check rather than the local IPA hostname.
All of these options assume that there's an HBAC rule to permit the user to log in to the Ipsilon server itself via the "ipsilon" service, which we require now.
Considering I'm writing this mail, it'll come as no surprise that I'm most interested in option 4.
I see two problems with option 4: 1) what interface to use, which is discussed below 2) sssd_be currently authenticates using the host keytab. In order to learn what host groups apply to a certain host, IIRC the hosts's memberof attribute is read. I'm not sure if a host can read another host's groups and if it currently does, whether it would continue working. But maybe this is something that could be solved by tuning the permissions on the server side?
SSSD only fetches HBAC rules from FreeIPA that affect the local host (unless the legacy src host option is enabled), so there'd need to be an option to enable fetching all rules instead. I'm not clear if there's a PAM attribute that could be used to pass the remote host name to SSSD for the check, so my thought was to add HBAC functionality to the infopipe (Ipsilon can already use the Infopipe for fetching user attributes). My first thought is something like an org.freedesktop.sssd.infopipe.HBAC DBus interface with an Evaluate method that takes hostname, username, and service name, and returns a boolean.
There were requests to implement authentication over the D-bus interface in the past and we were quite reluctant to them, but IIRC that was because PAM handles prompting for the secrets, passing auth tokens and it's just well battle-tested.
But I don't see the same issues with an authorization call.
I would prefer another interface than infopipe (authzpipe?), but in general, as long as the interface is restricted to authorization and not authentication, I don't see an inherent issue.
So, basically, if I were to work up patches to implement this option, would they have a chance of being accepted into SSSD? In the meantime we'll probably look at implementing one of option 2 or 3, but the SSSD option is appealing to me in the longer term.
Cheers.
-- HJ _______________________________________________ sssd-devel mailing list -- sssd-devel@lists.fedorahosted.org To unsubscribe send an email to sssd-devel-leave@lists.fedorahosted.org
On ti, 27 kesä 2017, Jakub Hrozek wrote:
On Tue, Jun 27, 2017 at 11:40:37AM +0100, Howard Johnson wrote:
In Ipsilon, we recently (OK, about a year ago) added an authorisation stack. This allows us to control, Ipsilon-side, which users are permitted to log into which service providers. Our authorisation plugin functions are currently fairly limited, basically using user group membership to control which service providers a user has access to. One of the things we'd like to support is using FreeIPA's HBAC rules rather than user attributes directly. In my opinion, this makes it much more obvious what's going on and fits in better with FreeIPA's architecture.
There're a few options that have come up in discussions around this on #ipsilon and #sssd:
- Treat each service provider as a new service in FreeIPA. The most basic
HBAC rule would then be "<user> can log into <ipsilon server> via service <service provider>". Ipsilon can easily do a PAM_ACCT_MGMT PAM call (either using a PAM library, or by talking to SSSD directly using the PAM socket) with the appropriate service name. SSSD will then permit or deny the check based on the HBAC rules. This is nice and simple, but the permitted length / characters of service names could have a potential limit on what service providers can be authorised this way.
- Ipsilon fetches HBAC rules from FreeIPA and processes them itself. This
requires duplication of the HBAC processing logic in Ipsilon (although I believe the python bindings for libipa_hbac deal with most of the heavy lifting there)
correct. I think this would be the second-quickest path forward.
, and LDAP connectivity to the FreeIPA server(s), along with the appropriate login credentials. Ipsilon would need to have any appropriate retry / failover logic. With this method, we can create service providers as hosts in FreeIPA, and HBAC rules would be "<user> can log into <service provider> via service saml2" (or openidc, etc).
- Ipsilon uses the FreeIPA JSON-RPC API to call the hbactest API. This
moves the HBAC check to the FreeIPA server, where the logic already exists. This requires Ipsilon to have access to the FreeIPA API and the appropriate login credentials. Moving the HBAC checks into FreeIPA itself has load implications for the IPA servers. Again, this would permit HBAC rules of the style "<user> can log into <service provider> via saml2".
I think this is the quickest path forward.
- Add support to SSSD for performing HBAC checks for arbitrary FreeIPA
hosts. This lets SSSD deal with connections to FreeIPA, including authentication and failover, which it's already doing. Some mechanism would be needed for Ipsilon to pass the "destination host" to SSSD for use in the HBAC check rather than the local IPA hostname.
All of these options assume that there's an HBAC rule to permit the user to log in to the Ipsilon server itself via the "ipsilon" service, which we require now.
Considering I'm writing this mail, it'll come as no surprise that I'm most interested in option 4.
I see two problems with option 4:
- what interface to use, which is discussed below
- sssd_be currently authenticates using the host keytab. In order
to learn what host groups apply to a certain host, IIRC the hosts's memberof attribute is read. I'm not sure if a host can read another host's groups and if it currently does, whether it would continue working. But maybe this is something that could be solved by tuning the permissions on the server side?
I think we currently have no limitation on memberof attribute access for authorized users. E.g. host/.. principal bind to LDAP gives you access to memberof attribute without any limitation.
We are going to introduce a special type of groups where membership reading would be limited to some conditions but this would not be relevant to HBAC, at least from my current understanding of the situation. This is to support organizational groups, not host-based access rights.
So I think option 4 is OK from the server perspective. Note also that option 3 needs an authenticated access too and might just use either ipsilon's principal (HTTP/ipsilon.hostname) or some specialized one, or host/ principal as well. This is not going to be much different to option 4 with regards to authentication details.
SSSD only fetches HBAC rules from FreeIPA that affect the local host (unless the legacy src host option is enabled), so there'd need to be an option to enable fetching all rules instead. I'm not clear if there's a PAM attribute that could be used to pass the remote host name to SSSD for the check, so my thought was to add HBAC functionality to the infopipe (Ipsilon can already use the Infopipe for fetching user attributes). My first thought is something like an org.freedesktop.sssd.infopipe.HBAC DBus interface with an Evaluate method that takes hostname, username, and service name, and returns a boolean.
There were requests to implement authentication over the D-bus interface in the past and we were quite reluctant to them, but IIRC that was because PAM handles prompting for the secrets, passing auth tokens and it's just well battle-tested.
But I don't see the same issues with an authorization call.
I would prefer another interface than infopipe (authzpipe?), but in general, as long as the interface is restricted to authorization and not authentication, I don't see an inherent issue.
Yep. I guess the whole story is about extending SSSD cache handling to support storing multiple hosts' HBAC rules details.
Cheers for the feedback.
On 2017-06-28 12:14, Alexander Bokovoy wrote:
We are going to introduce a special type of groups where membership reading would be limited to some conditions but this would not be relevant to HBAC, at least from my current understanding of the situation. This is to support organizational groups, not host-based access rights.
I guess at worst for this we might need a new set of role/privilege/permission that would allow viewing of all memberOf attributes.
On ti, 27 kesä 2017, Jakub Hrozek wrote:
There were requests to implement authentication over the D-bus interface in the past and we were quite reluctant to them, but IIRC that was because PAM handles prompting for the secrets, passing auth tokens and it's just well battle-tested.
Yeah, that absolutely makes sense.
But I don't see the same issues with an authorization call.
Excellent :)
I would prefer another interface than infopipe (authzpipe?), but in general, as long as the interface is restricted to authorization and not authentication, I don't see an inherent issue.
Would the authzpipe be another interface provided by sssd_ifp, or would you want another process (say, sssd_azp) to provide it?
I guess then if I were to start working up some patches, I wouldn't be wasting everyone's time? :)
On Wed, Jun 28, 2017 at 03:29:02PM +0100, Howard Johnson wrote:
Cheers for the feedback.
On 2017-06-28 12:14, Alexander Bokovoy wrote:
We are going to introduce a special type of groups where membership reading would be limited to some conditions but this would not be relevant to HBAC, at least from my current understanding of the situation. This is to support organizational groups, not host-based access rights.
I guess at worst for this we might need a new set of role/privilege/permission that would allow viewing of all memberOf attributes.
On ti, 27 kesä 2017, Jakub Hrozek wrote:
There were requests to implement authentication over the D-bus interface in the past and we were quite reluctant to them, but IIRC that was because PAM handles prompting for the secrets, passing auth tokens and it's just well battle-tested.
Yeah, that absolutely makes sense.
But I don't see the same issues with an authorization call.
Excellent :)
I would prefer another interface than infopipe (authzpipe?), but in general, as long as the interface is restricted to authorization and not authentication, I don't see an inherent issue.
Would the authzpipe be another interface provided by sssd_ifp, or would you want another process (say, sssd_azp) to provide it?
I think reusing the same responder is OK, but I would prefer another interface. I don't know if we have any issues supporting multiple interfaces from the same process, but if we do, it's a bug and should be fixed.
I guess then if I were to start working up some patches, I wouldn't be wasting everyone's time? :)
Could you please write up a design page first?
Check e.g. https://docs.pagure.org/SSSD.sssd/design_pages/non_posix_support.html
The source can be found in our docs repo: https://pagure.io/SSSD/docs here: https://pagure.io/SSSD/docs/blob/master/f/design_pages/non_posix_support.rst (submitting a PR against the docs repo is enough)
On 2017-06-28 15:39, Jakub Hrozek wrote:
I think reusing the same responder is OK, but I would prefer another interface. I don't know if we have any issues supporting multiple interfaces from the same process, but if we do, it's a bug and should be fixed.
I think technically the current infopipe API consists of multiple interfaces, so adding e.g. org.freedesktop.sssd.authzpipe shouldn't be a problem. I can test that easily enough, though.
Could you please write up a design page first?
Yep, will do. Thanks!
On ke, 28 kesä 2017, Howard Johnson wrote:
Cheers for the feedback.
On 2017-06-28 12:14, Alexander Bokovoy wrote:
We are going to introduce a special type of groups where membership reading would be limited to some conditions but this would not be relevant to HBAC, at least from my current understanding of the situation. This is to support organizational groups, not host-based access rights.
I guess at worst for this we might need a new set of role/privilege/permission that would allow viewing of all memberOf attributes.
Correct. Though the way how HBAC rules are evaluated right now by SSSD assumes we are dealing with POSIX users/groups there, so a subject of the HBAC check is a user with POSIX group membership. This membership information is already flattened so that intermediate non-POSIX group membership is not there anymore because POSIX groups are non-hierarchical. Given that we would specifically target those organizational groups for non-POSIX use, I don't think we lose anything here.
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