Spring RestTemplate seems to not be thread-safe wrt headers - spring

Question

I have a Spring web client which posts to a Spring web server (the same URL) using two different basic-auth users. Is it a known issue that I can not use a single RestTemplate for both?
When I use a single RestTemplate, and the requests are nearly simultaneous (in different threads), though I specify different users in the header, the receiving server thinks they're from the same user! Note that the request and the headers (and the body of the post) are newly allocated for each request.
It works fine, when I use a single RestTemplate and put a synchronized() around the call to
response = RestTemplate.exchange(url, method, requestParams, MyResponse.class)
I've also tried creating two RestTemplate instances, one for each user - (each built with a RestTemplateBuilder) that works, too. I'll keep this solution, but it surprises me that it's needed.
Is this a known issue?
(I see stackOverflow answers that a RestTemplate is thread-safe after constructed, but the headers are passed in with the request, not as a setting on the already-constructed RestTemplate...)
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Here's an example of 2 different calls, using 2 different RestTemplates because there were sometimes problems in using the same:
public OperationStatus getOpStatus(String gufi) {
HttpEntity<String> requestParams = new HttpEntity<>(Utils.createBasicHeader(cfg.getManager(), cfg.getManPass()));
ResponseEntity<OperationStatus> restResponse = null;
try {
restResponse = managerRestTemplate.exchange(
cfg.getNussOpApiPath(), HttpMethod.GET, requestParams, OperationStatus.class);
} catch (RestClientException e) {
...
}
OperationStatus opState = restResponse.getBody();
opState.setHttpStatusCode(String.valueOf(restResponse.getStatusCodeValue()));
return opState;
}
Here was a method to do a post, using the priority to switch rest templates (at the time, the target server recognized the priority by the privileges of the user)
UTMRestResponse doPost(Object objToSend, String url, String msg) throws IOException {
String user = cfg.getOpUser();
String pass = cfg.getOpPass();
RestTemplate restTemplate = opUserRestTemplate;
boolean isPriorityOp = false;
if ( objToSend instanceof OpPost) {
OpPost post = (OpPost) objToSend;
String flightNum = post.getFlightNumber();
isPriorityOp = Boolean.TRUE.equals(post.getPriorityOp()); // null is false
} else if ( objToSend instanceof PositionPost) {
PositionPost post = (PositionPost) objToSend;
isPriorityOp = Boolean.TRUE.equals(post.getPriorityOp()); // null is false
}
if (isPriorityOp) {
user = cfg.getUserEmergency();
pass = cfg.getPassEmergency();
restTemplate = emergRestTemplate;
}
String jsonToSend = CommonsObjectMapper.get().writeValueAsString(objToSend);
HttpEntity<String> requestParams = new HttpEntity<>(jsonToSend, Utils.createBasicHeader(user, pass));
UTMRestResponse restResponse = restTemplate.exchange(
url, HttpMethod.POST, requestParams, UTMRestResponse.class).getBody();
if (restResponse.getHttpStatusCode().startsWith("4")) {
String fmt = "Status:{}, url:{}, jsonSent:{}, response:{}";
logger.error(fmt, restResponse.getHttpStatusCode(), url, jsonToSend, restResponse.getMsg());
}
return restResponse;
}