How to change the generated OTP from alphanumeric to numeric in multi-factor authentication?

NOTE: The following resolution requires customization and should only be implemented at the discretion of your team. Liferay Support will not be able to assist with designing or implementing customizations.

Issue

The Multi-Factor Authentication (MFA) one-time password (OTP) is generated in an alphanumeric format. How can it be changed to numeric only?

Environment

Liferay DXP 7.4

Resolution

At the time of writing this article, there is no out-of-the-box feature available to change the password from alphanumeric to numeric only.
However, this requirement could be achieved by overriding SendMFAEmailOTPMVCResourceCommand class

Modify the following code:

@Component(
        property = {
                "javax.portlet.name=" + "com_liferay_multi_factor_authentication_portlet_web_internal_portlet_MFAEmailOTPVerifyPortlet",
                "mvc.command.name=/mfa_email_otp_verify/send_mfa_email_otp",
                "service.ranking:Integer=100"},
        service = MVCResourceCommand.class)
public class SendMFAEmailOTPMVCResourceCommand implements MVCResourceCommand {
    public static final String KEY1 = "0123456789";
    private static final String[] _KEYS = {KEY1};

String generatedMFAEmailOTP = PwdGenerator.getPassword(mfaEmailOTPConfiguration.otpSize(),_KEYS);
}

This change configures the OTP generator to use only numeric characters.

Additional Information

SendMFAEmailOTPMVCResourceCommand