@UnstableApi
    public static ConnectProxyConfig connect(InetSocketAddress proxyAddress, String username, String password,
                                             HttpHeaders headers, boolean useTls) {
        requireNonNull(proxyAddress, "proxyAddress");
        requireNonNull(username, "username");
        requireNonNull(password, "password");
        requireNonNull(headers, "headers");
        return new ConnectProxyConfig(proxyAddress, username, password, headers, useTls);
    }
Creates a {@code ProxyConfig} configuration for CONNECT protocol.

@param proxyAddress the proxy address
@param username the username
@param password the password
@param headers the {@link HttpHeaders} to send to the proxy
@param useTls whether to use TLS to connect to the proxy
core/src/main/java/com/linecorp/armeria/client/proxy/ProxyConfig.java