Comma-delimited is probably the way to go. RFC 7230 §3.2.2 establishes that you may combine multiple header fields with the same name by joining the values with

Comma-delimited is probably the way to go. RFC 7230 §3.2.2 establishes that you may combine multiple header fields with the same name by joining the values with commas (noting that as a special case for historical reasons, it isn't safe to do this with Set-Cookie). That is, X-Clacks-Overhead: GNU Terry Pratchett X-Clacks-Overhead: GNU Lain M. Banks should be equivalent to X-Clacks-Overhead: GNU Terry Pratchett, GNU Lain M. Banks