@Override
    String decodeChallenge(final String challenge) throws IllegalArgumentException {
        final byte[] bytes = challenge.getBytes(StandardCharsets.US_ASCII);
        final Base64 codec = new Base64();
        return new String(codec.decode(bytes), charset);
    }
Constructs a new BasicAuthenticationHandler with UTF-8 as the charset.
This default setting aligns with standard practices for encoding credentials in Basic Authentication.
httpclient5-testing/src/main/java/org/apache/hc/client5/testing/auth/BasicAuthenticationHandler.java