See MP Rest Client Issue [217|MP Rest Client overlooks Collection handling in params]
Users would like to configure how the MP Rest Client will format query parameters when multiple values are specified for the same parameter key. Styles include the normal/expanded format like foo=v1&foo=v2&foo-v3 vs comma-separated like foo=v1,v2,v3 vs array syntax (which is heavily used in PHP servers) like foo=v1&foo=v2&foo=v3.
CXF already covers the first two cases. This issue should add array syntax and should update the MP Rest Client implementation to allow users to select between the different styles.