in src/main/java/software/amazon/msk/auth/iam/internals/AWS4SignedPayloadGenerator.java [117:134]
private Map<String, String> toKeyValueMap(SdkHttpFullRequest request,
AuthenticationRequestParams params) {
final Map<String, String> keyValueMap = new HashMap<>();
final Set<Map.Entry<String, List<String>>> parameterEntries = request.rawQueryParameters().entrySet();
parameterEntries.stream().forEach(
e -> keyValueMap.put(e.getKey().toLowerCase(), generateParameterValue(e.getKey(), e.getValue())));
keyValueMap.put(VERSION_KEY, params.getVersion());
keyValueMap.put(USER_AGENT_KEY, params.getUserAgent());
//Add the headers.
final Set<Map.Entry<String, List<String>>> headerEntries = request.headers().entrySet();
headerEntries.stream()
.forEach(e -> keyValueMap.put(e.getKey().toLowerCase(), e.getValue().get(0)));
return keyValueMap;
}