refac: hardening pass with multiple overhauls

api/pkg/validator/validator.go

@@ -1,9 +1,22 @@
 package validator
 
-import "github.com/go-playground/validator/v10"
+import (
+	"regexp"
+
+	"github.com/go-playground/validator/v10"
+)
+
+const inviteEmailTag = "inviteemail"
+
+var inviteEmailPattern = regexp.MustCompile(`^[^\s@]+@[^\s@.]+(\.[^\s@.]+)+$`)
 
 var Validate *validator.Validate
 
 func InitValidator() {
 	Validate = validator.New()
+	_ = Validate.RegisterValidation(inviteEmailTag, isInviteEmail)
+}
+
+func isInviteEmail(field validator.FieldLevel) bool {
+	return inviteEmailPattern.MatchString(field.Field().String())
 }