Which parameter needs to be adjusted to increase the SharePoint Agent header size so that it can accept cookie with size ~16KB?
Changes need to be made to two different configuration files for the Agent for SharePoint system to increase the maximum header size allowed.
Update the worker.ajp13.max_packet_size parameter in the SharePoint Agent \secure-proxy\proxy-engine\conf\server.conf (set in bytes, max value is 65536).
Add the LimitRequestFieldSize directive to the \secure-proxy\httpd\conf\httpd.conf file and set the limit higher than the 8k default (set in bytes, max value is 16384). CA recommends adding this directive immediately below the ServerName directive since placing it in other locations, such as at the bottom of the file, causes the setting to not take effect.
Restart Agent for SharePoint for the settings to take effect.
This same configuration also works for Access Gateway (formerly Secure Proxy Server) as well.