js: handle SHA-512/224 and SHA-512/256 in crypto.subtle.digest

The digest op fell through to SHA-256 for any unrecognized algorithm name,
so SHA-512/224 and SHA-512/256 silently returned a SHA-256 hash. Add the
two FIPS 180-4 truncated variants, which the AWS WAF challenge proof-of-work
(used by booking.com and other CloudFront/WAF sites) requires.

Fixes #314.

crates/obscura-js/src/ops.rs

@@ -1067,9 +1067,10 @@ fn op_binding_called(state: &OpState, #[string] name: &str, #[string] payload: &
 }
 
 /// Real WebCrypto `crypto.subtle.digest`. `algorithm` is the SubtleCrypto
-/// algorithm name (`SHA-1` / `SHA-256` / `SHA-384` / `SHA-512`); unknown
+/// algorithm name (`SHA-1` / `SHA-256` / `SHA-384` / `SHA-512`, plus the
-/// names fall through to SHA-256 to match the previous JS fallback. Returns
+/// FIPS 180-4 truncated variants `SHA-512/224` and `SHA-512/256`). Other
-/// the raw digest bytes so the JS shim can hand them back as an ArrayBuffer.
+/// names fall back to SHA-256. Returns the raw digest bytes so the JS shim
+/// can hand them back as an ArrayBuffer.
 #[op2]
 #[buffer]
 fn op_subtle_digest(#[string] algorithm: &str, #[buffer] data: &[u8]) -> Vec<u8> {
@@ -1080,6 +1081,8 @@ fn op_subtle_digest(#[string] algorithm: &str, #[buffer] data: &[u8]) -> Vec<u8>
         "SHA-256" => sha2::Sha256::digest(data).to_vec(),
         "SHA-384" => sha2::Sha384::digest(data).to_vec(),
         "SHA-512" => sha2::Sha512::digest(data).to_vec(),
+        "SHA-512/224" => sha2::Sha512_224::digest(data).to_vec(),
+        "SHA-512/256" => sha2::Sha512_256::digest(data).to_vec(),
         _ => sha2::Sha256::digest(data).to_vec(),
     }
 }