Incorrect regex in forRegex

[fizbin]

While auditing some internal code for a common mistake made in regex patterns, we discovered a vendored copy of this line:

handlers/proxy_headers.go

Line 25 in 3e03024

forRegex = regexp.MustCompile(`(?i)(?:for=)([^(;|,| )]+)`)

The line currently reads

	forRegex = regexp.MustCompile(`(?i)(?:for=)([^(;|,| )]+)`)

It was likely intended to read

	forRegex = regexp.MustCompile(`(?i)(?:for=)([^;, ]+)`)

however, even that is not correct according to rfc7239. If we wish to follow the RFC, then the forRegex should be defined as

	forRegex = regexp.MustCompile(`(?i)(?:for=)(?:([-!#$%&'*+.^`|~\w]+)|"((?:[\t \x21-\x27\x2A-\x5B\x5D-\x7E\x80-\xFF]|\\[\t -~\x80-\xFF])+)")`)

and in that case processing that uses forRegex will need to decide whether the first or second capture group matched and, in the case where the second capture group matched, do the appropriate replacement to remove backslashes.