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[Metadata-Support] Extending Metadata Query Protocol

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  • From: Jaime Perez Crespo <>
  • To: "" <>
  • Subject: [Metadata-Support] Extending Metadata Query Protocol
  • Date: Wed, 18 Mar 2015 13:25:26 +0000
  • Accept-language: en-US, nb-NO

Hi all,

Recently, we’ve incorporated MQP support to SimpleSAMLphp, in order to
dynamically retrieve metadata from a trusted MDX server, both for identity
and service providers. This is a valuable addition in my opinion, and we are
looking forward to improve it as much as possible.

One of the issues that we’ve observed is that using the Metadata Query
Protocol to fetch metadata for previously unknown entities introduces a
(potentially big) delay when serving the request that originated the query to
the MDX server. While this could be acceptable in certain circumstances, we
would like to be able to avoid this delay as much as possible by periodically
prefetching metadata from the MDX server. For that to be possible, I can
imagine the following requisites:

* To be able to query the MDX server for a list of all the entities served.
When I say “list of entities”, I mean a list of identifiers used by the MDX
implementation that can be used to request the metadata of a particular
entity (i.e. the entityID or its SHA-1).
* To be able to query the MDX server for a list of all the entities *modified
since* a specific date. This would allow us to query the server later only
for those entities that have been modified since the last request.

I understand the first one could be easily disregarded by using the MDX as a
standard metadata feed, that is, fetching the whole metadata set it serves,
processing, caching, and then proceeding onwards by leveraging the second
one. However, I see benefits on being able to iteratively retrieve entities
instead of a huge feed, like better performance and availability of entities.
In any case, both features would be interesting to make the Metadata Query
Protocol even more useful for big deployments, I think

Please share your thoughts and comments.

Jaime Pérez


"Two roads diverged in a wood, and I, I took the one less traveled by, and
that has made all the difference."
- Robert Frost

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