The RoundCube UI has support for some basic headers. You can "Add CC", "Add Bcc", "Add Reply-To" and "Add Followup-To". You can look for these strings in the code and extend the UI with headers of your choice. A possibility would be "Add Arbitrary Header", where q quick and dirty way to implement it would be to let the user enter the header using "Name: value" syntax, and parse it out. You could repeat that button three times so the user can add up to three custom headers.
As far as PGP headers go, you really don't want users to be mucking around with headers; PGP support ought to be integrated into the client.
This has been the subject of a long-standing trac ticket:
http://trac.roundcube.net/ticket/1440396
Earlier this year, an annoucement was made in this list by someone developing an OpenPGP plugin:
http://lists.roundcube.net/pipermail/dev/2013-January/022123.html
On 01.10.2013 18:51, Nick Edwards wrote:
I'm amazed that I can not locate a plugin, but I'm sure one must exist, on 2013, that allows eaxh user to add customer headers if they want, some users need to add the security headers, some even want to add their PGP header, but no obvious way to do it.
Am I having a blonde moment?
Nikki