public static Endpoint.Builder sigv4(Endpoint.Builder builder, Literal signingRegion, Literal signingService) {
        return builder.addAuthScheme(SIGV4,
                MapUtils.of(
                        SIGNING_NAME,
                        signingService,
                        SIGNING_REGION,
                        signingRegion));
    }
Adds SigV4 authentication to the provided endpoint builder.

@param builder the endpoint builder to augment.
@param signingRegion the signing region to use when signing.
@param signingService the name of the service to sign with.
@return the updated endpoint builder.
smithy-aws-endpoints/src/main/java/software/amazon/smithy/rulesengine/aws/language/functions/EndpointAuthUtils.java