Testing JWT Authentication in Postman, Playwright & Rest Assured (2026)

2026-07-17 · By Avinash Kamble, reviewed by Priyanka G.

Almost every API you test in 2026 uses JWT bearer tokens. This guide gives you copy-paste-ready scripts for the three tools QA teams actually run: Postman for exploratory + collection runs, Playwright for full E2E with UI, and Rest Assured for Java-based backend suites.

Do not log in inside every test. Grab a token in a setup step and inject it via header. Refresh only when it's within 60s of exp.

// collection-level pre-request
const token = pm.environment.get("access_token");
const exp = pm.environment.get("access_token_exp");
if (!token || Date.now()/1000 > exp - 60) {
  pm.sendRequest({
    url: pm.environment.get("auth_url") + "/token",
    method: "POST",
    header: { "Content-Type": "application/x-www-form-urlencoded" },
    body: { mode: "urlencoded", urlencoded: [
      { key: "grant_type", value: "password" },
      { key: "username", value: pm.environment.get("test_user") },
      { key: "password", value: pm.environment.get("test_pass") },
    ]},
  }, (err, res) => {
    const jwt = res.json().access_token;
    const payload = JSON.parse(atob(jwt.split(".")[1]));
    pm.environment.set("access_token", jwt);
    pm.environment.set("access_token_exp", payload.exp);
  });
}

// tests/fixtures/auth.ts
import { test as base, request } from "@playwright/test";
export const test = base.extend<{ token: string }>({
  token: async ({}, use) => {
    const ctx = await request.newContext();
    const res = await ctx.post(process.env.AUTH_URL + "/token", {
      form: { grant_type: "password", username: "qa", password: process.env.QA_PASS },
    });
    const { access_token } = await res.json();
    await use(access_token);
  },
});

// tests/orders.spec.ts
test("create order", async ({ token, request }) => {
  const res = await request.post("/api/orders", {
    headers: { Authorization: `Bearer ${token}` },
    data: { sku: "A1", qty: 2 },
  });
  expect(res.status()).toBe(201);
});

@BeforeAll
static void auth() {
  token = given()
    .contentType("application/x-www-form-urlencoded")
    .formParam("grant_type", "password")
    .formParam("username", System.getenv("QA_USER"))
    .formParam("password", System.getenv("QA_PASS"))
    .post(System.getenv("AUTH_URL") + "/token")
    .jsonPath().getString("access_token");
}

@Test
void createOrder() {
  given().header("Authorization", "Bearer " + token)
    .contentType(ContentType.JSON)
    .body(Map.of("sku", "A1", "qty", 2))
  .when().post("/api/orders")
  .then().statusCode(201);
}

• Send request with no Authorization header → 401.
• Send with tampered signature (change one char) → 401.
• Send with alg:none forged token → 401.
• Send with expired token (exp = yesterday) → 401.
• Send with token from another tenant → 403.

Instead of hand-crafting attack payloads, open the JWT Debugger, load a sample attack (alg=none, weak-secret, expired, kid-injection), copy the token, and paste it into your Postman/Playwright/Rest Assured negative-test suite.