@Override
    public String asHeaderValue() {
        if (headerValue != null) {
            return headerValue;
        }
        return headerValue = "Basic " + Base64.getEncoder().encodeToString(
                (username + ':' + password).getBytes(StandardCharsets.UTF_8));
    }
Returns the string that is sent as the value of the {@link HttpHeaderNames#AUTHORIZATION} header.
core/src/main/java/com/linecorp/armeria/common/auth/BasicToken.java