[tptacek]

There's also detached signatures and flexible tag matching, which lead to implementations that have provide rigid schemas with semantic passes to make sure there's no place to smuggle either additional signed content to confuse verifiers, or content that will get signed that changes the message semantics. The whole thing is deeply unsound. OIDC is no great shakes, but even 10 years ago nobody would ever design a signed message scheme that looked like SAML.