gomatrixserverlib rejects Authorization: X-Matrix ... headers that include optional whitespace around parameter pairs

[anoadragon453]

The spec states that the format of the Authorization header on the Federation API is given by RFC 7235. Part of that specification allows for zero or more spaces or tabs around the commas in the parameter list. For example, the following should be a valid Authorization header:

Authorization: X-Matrix origin=foo , key="ed25519:1",  sig="sig",		destination="bar"

Yet upon looking at gomatrixserverlib's source code, I believe it would reject this header:

gomatrixserverlib/fclient/request.go

Lines 321 to 351 in c2391f7

	func ParseAuthorization(header string) (scheme string, origin, destination spec.ServerName, key gomatrixserverlib.KeyID, sig string) {
	parts := strings.SplitN(header, " ", 2)
	scheme = parts[0]
	if scheme != "X-Matrix" {
	return
	}
	if len(parts) != 2 {
	return
	}
	for _, data := range strings.Split(parts[1], ",") {
	pair := strings.SplitN(data, "=", 2)
	if len(pair) != 2 {
	continue
	}
	name := pair[0]
	value := strings.Trim(pair[1], "\"")
	if name == "origin" {
	origin = spec.ServerName(value)
	}
	if name == "key" {
	key = gomatrixserverlib.KeyID(value)
	}
	if name == "sig" {
	sig = value
	}
	if name == "destination" {
	destination = spec.ServerName(value)
	}
	}
	return
	}

This fact was omitted from the summary of RFC 7235 in the spec, which is likely why it didn't make it into gomatrixserverlib as well. That is now being corrected: matrix-org/matrix-spec#1818

The code should be updated to allow whitespace in the parameter list in the header, such that any homeserver implementations following the spec would not have their federation requests rejected by homeservers that rely on gomatrixserverlib.

See matrix-org/matrix-spec#1817 for more context.