Signing metadata

[Peter Schober]

* Cantor, Scott <cantor.2 at osu.edu> [2017-06-21 19:39]:
> The most prevalent use case for automated metadata exchange is
> changing a key. The SP has no facility for adding a key at runtime
> that doesn't end up in the generated metadata, or including a key in
> the metadata before it gets into the runtime. Part of the process
> for changing a key involves a guarantee that a key won't get used
> until after the metadata change propagates or a guarantee that the
> key can be used before it ends up in the metadata. By definition
> then, you can't use metadata for the most important thing it's meant
> to be used for in an automated situation if you generate it with no
> intervening gap or you'll end up with an outage.

FWIW: Unless there are added subtleties I'm not aware of SimpleSAMLphp
solved this by having a separate config parameter for the new key (to
be introduced in a key rollover), combined with special behaviour that
uses the key from the other/new parameter only for decryption, but not
for signing:
https://simplesamlphp.org/docs/stable/saml:keyrollover

Metadata will be dynamically updated for both keys, and the "old"
(non-new) key will not be listed for encryption anymore.

-peter