@JsonIgnore
    public boolean isRegistrationEnabled() {
        return acceptedEmailPattern != null;
    }
The regular expression that controls which email addresses users are allowed to register
during the multifactor authentication flow. If no pattern is defined (default),
registration flow will be disabled. An example email address might
be {@code ^[a-zA-Z0-9._%+-]+@example\.org$}.
api/cas-server-core-api-configuration-model/src/main/java/org/apereo/cas/configuration/model/support/mfa/simple/CasSimpleMultifactorAuthenticationEmailProperties.java