public String generate() {
        return generate(System.currentTimeMillis() / 1000);
    }
Generates a TOTP code of the given length using the current system time.

@return
    The TOTP code which corresponds to the current system time, having
    exactly the given length.

@throws IllegalArgumentException
    If the given length is invalid as defined by the TOTP specification.
extensions/guacamole-auth-totp/src/main/java/org/apache/guacamole/totp/TOTPGenerator.java