Is an HTTP client allowed to send multiple headers with the same name?

Question

I\'m aware that HTTP servers can send headers with duplicate keys (at least Set-Cookie comes to mind), but is there a plausible reason for clients to do this?

Answer 1

a) It might be easier when multiple pieces of code are involved,

b) It can be unavoidable for certain fields such as Set-Cookie (see https://greenbytes.de/tech/webdav/rfc7230.html#rfc.section.3.2.2.p.4).