Java APIs are not handling headers in a case insensitive way

API

Java

Expected Behavior

When adding headers like:

Map<String, List<String>> headers = new HashMap<>();
headers.put("key", Collections.singletonList("a"));
headers.put("KEY", Collections.singletonList("b"));
ws.url("http://example.com").setHeaders(headers);

Both "a" and "b" must be returned when calling getHeaderValues("key").

The same should apply to response headers.

Actual Behavior

Only "b" is present when calling getHeaderValues("key").

Start by locating the Java API implementations of setHeaders and getHeaderValues, then inspect how request and response headers are stored and looked up. Reproduce the example with both "key" and "KEY" and add or update coverage for each direction. Done means getHeaderValues("key") returns both values for request and response headers.