No way of disabling sigv4 auth scheme (and signing) with AwsCodegen model

[GJason88]

There is some logic that makes it so if there is an auth scheme for an operation in the model, it uses it.

AwsCodegen has a sigv4 auth scheme, which when isn't known about before its addition to a model, results in a NoMatchingAuthSchemeError:

source: NoMatchingAuthSchemeError(
    ExploredList {
        items: [
            ExploredAuthOption {
                scheme_id: AuthSchemeId {
                    scheme_id: "sigv4",
                },
                result: NoIdentityResolver,
            },
        ],
        truncated: false,
    },
),

The issue is that there is no easy way to disable the sigv4 auth scheme (and signing).

This may be relevant: https://github.com/smithy-lang/smithy-rs/pull/3087/files

---

We tried (without success) modifying the smithy model using optionalAuth like:

in model/main.smithy:

$version: "2.0"

namespace <namespace>

apply <operation> @optionalAuth

in smithy-build-template.json:

{
  "version": "1.0",
  "projections": {
    "<name>": {
      "imports": ["model/main.smithy"],
...

---

The only way we could get it working was using a gross hack to:

• sign with dummy creds
• remove the signature with an interceptor

#[derive(Debug)]
struct DropAuthHeaderIntercepter;
impl Intercept for DropAuthHeaderIntercepter {
    fn name(&self) -> &'static str {
        "DropAuthHeaderInterceptor"
    }
    fn modify_before_transmit(
        &self,
        context: &mut BeforeTransmitInterceptorContextMut<'_>,
        _runtime_components: &RuntimeComponents,
        _cfg: &mut ConfigBag,
    ) -> Result<(), BoxError> {
        context.request_mut().headers_mut().remove("Authorization");
        Ok(())
    }
}

and in the config builder:

builder()
    .interceptor(DropAuthHeaderIntercepter)
    .credentials_provider(Credentials::for_tests())
...