`uriSchemePresentment`: the verifier's error response body is discarded by a bare `check(...)`

[mc1100]

Version: observed on 0.99.0; re-checked against main @ 145e9e1a — unchanged.

What happens

When a verifier rejects a presentation response, uriSchemePresentment asserts the status with a bare check(...) and drops the body:

multipaz/multipaz/src/commonMain/kotlin/org/multipaz/presentment/uriSchemePresentment.kt

Line 162 in 145e9e1

check(postResponseResponse.status == HttpStatusCode.OK)

The wallet therefore receives:

IllegalStateException: Check failed.

The verifier's actual explanation — the only thing that tells a user or a developer why the presentation was refused — is never read. Because check(...) without a message produces a fixed string, the app cannot distinguish this failure from any other check in the same function either.

Suggested fix

Read the response body and include it, along with the status code, in the thrown exception — the same shape as the neighbouring reader-side checks at L268-L269, which do report the status. A dedicated exception type carrying status + body would be better still, since a wallet usually wants to show the verifier's message rather than a stack trace.

Related

• Relax Content-Type header check for Direct Post Response redirect_uri #1543 (closed, fixed in SdJwt: Handle SD-JWTs with a single disclosure for age_equal_or_over. #1746) relaxed the Content-Type check two lines below this one, so this function has already been through one round of this treatment.

Workaround we ship

Our presenter string-matches "Check failed." and substitutes a readable sentence. Matching on an exception message is exactly as fragile as it sounds.