Separate second-factor verification and delivery from auth (#40)

backend/product/customers/model/email.go

@@ -0,0 +1,16 @@
+package model
+
+import (
+	merrors "git.sendico.io/tech/sxchnge/shared/errors"
+	"net/mail"
+	"strings"
+)
+
+func NormalizeEmail(email string) (string, error) {
+	email = strings.ToLower(strings.TrimSpace(email))
+	a, err := mail.ParseAddress(email)
+	if err != nil || a.Address != email || len(email) > 254 {
+		return "", merrors.InvalidArgument("valid email required")
+	}
+	return email, nil
+}