private String basic(String username, String password) {
      String token = username + ":" + password;
      byte[] bytes = token.getBytes(StandardCharsets.ISO_8859_1);
      String encoded = Base64.getEncoder().encodeToString(bytes);
      return "Basic " + encoded;
    }
Client that supports a {@link java.net.Proxy}.
core/src/main/java/feign/Client.java