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- Some SPs may not be able to use the AuthnRequest mechanism due to software or other limitations. Are they simply out of luck?
- One option may be to use additional software to generate requests on behalf of the broken SP, although this isn't guaranteed to work with all SPs. Otherwise, such SPs will be forced to rely on OOB configuration of IdPs.
- How is the AuthnRequest configured using the Shib SP? The simpleSAMLphp SP?
- Shibboleth SPs can rely on the
authnContextClassRef
setting to control the value requested when particular resources are accessed. To include multiple values in a request, the AuthnRequest "template" mechanism described in the SessionInitiator documentation can be used.
- Shibboleth SPs can rely on the
- Boarding process: Since an IAQ in metadata makes a statement about certification (not live service), how does an SP determine that an IdP supports assurance operationally (ala attribute support)? One approach is to include
<saml:Attribute>
elements in IdP metadata. Other approaches?- There is no metadata support for this requirement. SPs should be able to handle errors returned by IdPs that indicate the requested assurance level was not supported. The federation should help establish guidelines for describing such errors, perhaps with a FAQ page that could be linked in.
- Does the Shib SP software support the metadata check? Does the simpleSAMLphp SP?
- The Shibboleth SP can extract and make available the entity attribute value in a variable along with user attributes, and use the variable in authorization policy. This is described under "metadata attribute extraction".
- What matching rules are recommended, or acceptable?
- How is an SP supposed to "know" that Silver is acceptable in lieu of Bronze? Is there a role for InCommon to provide "advice"?
- How should an SP perform LoA escalation to allow for a need for increased LoA in an application when a user transitions from a context that needs little or no assurance, to a context that requires a higher LoA?
IdP behavior
Ideally IdPs will receive a desired IAQ from an SP in an AuthnRequest to initiate the process. The IdP compares the requested IAQ to its matching rules and interacts with the local IdM system to determine if the current user meets the requirements. If so, the appropriate IAQ is returned in the AuthnContext element in the assertion; if not, an error is returned.
Issues
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- The Shibboleth IdP directly supports only "exact" matching of requested IAQs, and SAML requires that such matchiing be exact (it does not allow for "equivalence"). Supporting more flexible comparison operators requires implementing a custom login handler.
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- Returning Silver is not permissible if the request asks for Bronze and uses "exact" matching. It would be permissible if "minimum" were specified, but a custom login handler would be needed.
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- The AuthnContext element that various groups decided to use for expressing them does not directly support more than one IAQ at a time. In theory an "umbrella" IAQ could be defined to capture combinations, but this would be complex to express and not supported widely.
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- It is virtually certain that suporting assurance in any but the most trivial of ways will require a custom login handler. It will take time to develop patterns and common requirements that could be factored into reusable code.
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- It seems likely that IdPs should express the IAQ appropriate for a user's session if they can.
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- A SAML IdP always sends some form of AuthnContext information. By convention, that is being used to carry an IAQ. In Shibboleth, the term in the IdP for this data element is the "authentication method".
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See Assurance - Identity Provider Behavior.
References
- SAML V2.0 Core
- SAML V2.0 Metadata Extension for Entity Attributes
- SAML V2.0 Identity Assurance Profiles
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