Compile the email regex only once

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

internal/controlplane/handlers_authz.go

@@ -604,11 +604,15 @@ func (s *Server) removeRole(
 	}, nil
 }
 
+var emailRegex *regexp.Regexp
+
 // isEmail checks if the subject is an email address or not
 func isEmail(subject string) bool {
 	// Define the regular expression for validating an email address
 	const emailRegexPattern = `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$`
-	emailRegex := regexp.MustCompile(emailRegexPattern)
+	if emailRegex == nil {
+		emailRegex = regexp.MustCompile(emailRegexPattern)
+	}
 	return emailRegex.MatchString(subject)
 }