fix(lib): make challenge validation fully deterministic

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/challenge/challenge.go

@@ -5,6 +5,7 @@ import "time"
 // Challenge is the metadata about a single challenge issuance.
 type Challenge struct {
 	ID         string            `json:"id"`         // UUID identifying the challenge
+	Method     string            `json:"method"`     // Challenge method
 	RandomData string            `json:"randomData"` // The random data the client processes
 	IssuedAt   time.Time         `json:"issuedAt"`   // When the challenge was issued
 	Metadata   map[string]string `json:"metadata"`   // Challenge metadata such as IP address and user agent