fix(endpoint): use sigv4a signing region override (#4054)

* fix(endpoint): use sigv4a signing region override

* fix(endpoint): use conditional operator for populating multiRegionOverride

Co-authored-by: Trivikram Kamat <[email protected]>

Author: kuhe

packages/middleware-signing/src/middleware.ts

@@ -24,14 +24,16 @@ export const awsAuthMiddleware =
 
       // TODO(identityandauth): call authScheme resolver
       const authScheme: AuthScheme | undefined = context.endpointV2?.properties?.authSchemes?.[0];
+      const multiRegionOverride: string | undefined =
+        authScheme?.name === "sigv4a" ? authScheme?.signingRegionSet?.[0] : undefined;
 
       const signer = await options.signer(authScheme);
 
       const output = await next({
         ...args,
         request: await signer.sign(args.request, {
           signingDate: getSkewCorrectedDate(options.systemClockOffset),
-          signingRegion: context["signing_region"],
+          signingRegion: multiRegionOverride || context["signing_region"],
           signingService: context["signing_service"],
         }),
       }).catch((error) => {