@CanIgnoreReturnValue
    public DuoSecurityUserAccount addAttribute(final String key, final String value) {
        if (!StringUtils.equalsAnyIgnoreCase("null", value) && StringUtils.isNotBlank(value)) {
            this.metadata.put(key, value);
        }
        return this;
    }
Add attribute.

@param key   the key
@param value the value
@return the duo security user account
support/cas-server-support-duo-core-mfa/src/main/java/org/apereo/cas/adaptors/duo/DuoSecurityUserAccount.java