Use Spring SSL bundle in SAML2 signing

[gertvv]

Expected Behavior

When acting as a SAML2 client, allow the lovely Spring SSL bundles to be used to specify the certificates in configuration. For example, by setting spring.security.saml2.relyingparty.registration.<reg-id>.signing.credentials.bundle.

Current Behavior

The private-key-location and certificate-key-location must be set separately and don't seem to have useful functionality offered by the SSL bundles, such as loading from a keystore and decrypting the private key.

Context

I'm looking for good ways to inject these secrets into the configuration and ideally without decrypting the key file on disk.

[jzheaux]

I think this sounds reasonable, though it would be something that Spring Boot would need to support as they are using those properties to construct an instance of RelyingPartyRegistration. Will you please file a ticket there and cc me in the description? I'd be happy to help coordinate.