var client = java.net.http.HttpClient.newHttpClient();
String token = "eyJ..."; // put your access token here

var req = java.net.http.HttpRequest.newBuilder()
    .uri(URI.create("https://api.example.com/resource"))
    .header("Authorization", "Bearer " + token)
    .header("Content-Type", "application/json")
    .POST(java.net.http.HttpRequest.BodyPublishers.ofString("{\"ping\":\"pong\"}"))
    .build();

var res = client.send(req, java.net.http.HttpResponse.BodyHandlers.ofString());
System.out.println(res.statusCode() + " " + res.body());

OkHttpClient client = new OkHttpClient.Builder()
    .addInterceptor(chain -> {
        String token = "eyJ..."; // inject per request or from a provider
        Request req = chain.request().newBuilder()
            .addHeader("Authorization", "Bearer " + token)
            .build();
        return chain.proceed(req);
    })
    .build();

Request request = new Request.Builder()
    .url("https://api.example.com/resource")
    .post(RequestBody.create("{\"ping\":\"pong\"}", MediaType.get("application/json")))
    .build();

try (Response resp = client.newCall(request).execute()) {
    System.out.println(resp.code());
}

var httpClient = HttpClients.custom()
    .addRequestInterceptorFirst((HttpRequest request, EntityDetails entity, HttpContext ctx) -> {
        request.addHeader("Authorization", "Bearer " + "eyJ...");
    })
    .build();

var post = new HttpPost("https://api.example.com/resource");
post.setHeader(HttpHeaders.CONTENT_TYPE, "application/json");
post.setEntity(new StringEntity("{\"ping\":\"pong\"}", StandardCharsets.UTF_8));

try (var resp = httpClient.execute(post)) {
    System.out.println(resp.getCode());
}

@Bean
WebClient webClient() {
  return WebClient.builder()
      .filter((req, next) -> {
        String token = "eyJ..."; // inject from a bean that caches/refreshes
        ClientRequest r = ClientRequest.from(req)
            .header(HttpHeaders.AUTHORIZATION, "Bearer " + token).build();
        return next.exchange(r);
      })
      .build();
}

// use it
webClient().post().uri("https://api.example.com/resource")
  .contentType(MediaType.APPLICATION_JSON)
  .bodyValue(Map.of("ping","pong"))
  .retrieve().toEntity(String.class).block();

RestTemplate rt = new RestTemplate();
rt.getInterceptors().add((req, body, ex) -> {
  req.getHeaders().setBearerAuth("eyJ...");
  return ex.execute(req, body);
});
ResponseEntity<String> resp = rt.getForEntity("https://api.example.com/resource", String.class);

@Bean
public RequestInterceptor bearerAuth() {
  return template -> template.header("Authorization", "Bearer " + "eyJ...");
}

BindingProvider bp = (BindingProvider) port;
Map<String, List<String>> headers = new HashMap<>();
headers.put("Authorization", List.of("Bearer eyJ..."));
bp.getRequestContext().put(MessageContext.HTTP_REQUEST_HEADERS, headers);

var client = HttpClient.newHttpClient();
var form = URLEncoder.encode("grant_type","UTF-8") + "=client_credentials" +
           "&" + URLEncoder.encode("client_id","UTF-8") + "=" + URLEncoder.encode(System.getenv("OIDC_CLIENT_ID"),"UTF-8") +
           "&" + URLEncoder.encode("client_secret","UTF-8") + "=" + URLEncoder.encode(System.getenv("OIDC_CLIENT_SECRET"),"UTF-8");

var req = HttpRequest.newBuilder(URI.create("https://idp.example.com/oauth2/token"))
    .header("Content-Type", "application/x-www-form-urlencoded")
    .POST(HttpRequest.BodyPublishers.ofString(form))
    .build();

var res = client.send(req, HttpResponse.BodyHandlers.ofString());
String token = new org.json.JSONObject(res.body()).getString("access_token");