code: public Collection<String> getAllowedHeaders(Collection<String> requestHeaders) {
  
  		Constraint.ensureNotNull(requestHeaders, "Null headers");
  		Set<String> rtAllowedHeaders = new HashSet<String>(allowedHeaders);
  		rtAllowedHeaders.addAll(requestHeaders);
  
  		return rtAllowedHeaders;
  	}
docs: Return all headers allowed by the resource, including the preflight request headers
  
  @param requestHeaders
  @return