commons-httpclient 3.x sends multiple Cookie request headers and Apache httpd/mod_proxy merges those into one Cookie header separated by comma (,)

Issue

• Apache httpd/mod_proxy merges multiple Cookie request header into one Cookie header separated by comma (,). Is this expected behavior? Is there any configurable parameter to change Apache httpd to use semicolon (;) instead?

• When I use commons-httpclient 3.x as a client, commons-httpclient 3.x adds multiple Cookie headers in one request like:

  GET /example/ HTTP/1.1
  User-Agent: ...
  Host: ...
  ...
  Cookie: NAME1=VALUE1
  Cookie: NAME2=VALUE2
  

  then Apache httpd/mod_proxy merges those into one Cookie header separated by comma (,) and forward it to the backend server:

  Cookie: NAME1=VALUE1, NAME2=VALUE2
  

  This behavior is not compatible with RFC6265 compliant server like Tomcat 8.5. And same issue happens when EAP 7 (Undertow) run as a backend server, too.