Considerations for exposing a SAML Service Provider to users and institutions registered with other Identity Federations via Interfederation arrangements (such as eduGAIN).
Access control
No assumptions should be made about the provenance or quality of identities from federated or interfederated IDPs based purely on successful authentication at a SAML IDP. If your service should only be available to certain user groups (e.g. students, faculty or staff at academic institutions) be sure to enforce this via explicit access control configuration based on attributes sent by the SAML IDP.
That avoids any surprises with regard to account issuing practices at other institutions or IDPs.
Metadata
Load SAML Metadata that also (i..e, in addition to eduID.at member SPs) includes entities known via Interfederation agreements, such as eduGAIN:
As always, use the provided Metadata Verification Key to make sure the metadata is authentic and hasn't been tampered with.
For the Shibboleth SP check out the complete configuration examples provided.
Operational aspects
The interfederation-enabled SAML 2.0 Metadata document (see above) is much larger (1-2 orders of magnitude) than the one only containing entities covered by the eduID.at policies. So make sure the machine your SAML SP implementation runs on has sufficient memory (RAM) available.
xmldsig-signature validation on these large documents may also take significant CPU resources (relevant when updating metadata every few hours or every day), but adding more CPU cores to a machine will not typically speed up this process significantly as it cannot be parallelised.
The Shibboleth SP software in particular has an issue only affecting its first start, when no previously downloaded, validated and cached metadata is available locally. The Shibboleth wiki provides some ways of dealing with that (e.g. by adding a configuration snippet that disables systemd's process start timeout). Also manually starting shibd before (re-)restarting it via the service manager (systemd or otherwise) should take care of that issue.
Be sure to follow our configuration examples, particularly with regards to the verifyBackup="false" setting on the Signature MetadataFilter.
IDP Discovery
Manually managing lists of Identity Providers users may log in from does not scale and may also not provide a proper user experience. It will therefore be necessary to deploy some kind of IDP discovery service, using additional software components which allow subjects to easily choose their preferred IDPs(s) from those available via interfederation. The eduID.at Demo SP currently demonstrates use of 3 different IDP discovery interfaces.
Fallback discovery services
If all else fails you can make use of one of the central "fallback" discovery interface provided by ACOnet.
There's currently one central "fallback" IDP Discovery Service avalable within eduID.at that's Interfederation-enabled:
This instance of the SWITCHwayf software may be more familiar to subjects from ACOnet institutions since older versions have been in use since 2007. This software still works (without its dynamic features) when JavaScript is disabled in the web browser (though not much else on the web will work in such a setup).
See Discovery Services for more, including references to Seamless Access.
Prepare for missing attributes from IDPs
Consider handling any access errors due to missing attributes as gracefully as possible. That includes giving precise instructions to the subject on what failed, why and what to do about it. Using information from SAML metadata support or technical contact data for the IDP should be offered.
TODO: More technical information to come.
Notify ACOnet
To make your Service Provider available to subjects from other interfederated institutions contact ACOnet in order for your entity to become visible to eduGAIN (and from there to other eduGAIN-participating federations and institutions).
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