How to test Preemptive Authentication in Rest Assured

  

What is Preemptive Authentication?

In preemptive authentication, the client sends the credentials (username & password) in the very first request, rather than waiting for the server to challenge it (with a 401 unauthorized response).

This can improve performance by skipping an extra request-response cycle.

To use preemptive basic auth in Rest Assured:

• Use .auth().preemptive().basic(username, password)

• This sends the Authorization header directly with the GET request.

• You can validate response data with assertions.

API to be tested:

https://postman-echo.com/basic-auth

This endpoint requires Basic Authentication

Username: "postman"

Password: "password"

Java Code using Rest Assured:

import io.restassured.RestAssured;
import io.restassured.response.Response;

import static io.restassured.RestAssured.*;
import static org.hamcrest.Matchers.*;

public class PreemptiveAuthTest {

    public static void main(String[] args) {

        // Base URI
        RestAssured.baseURI = "https://postman-echo.com";

        // Preemptive Basic Auth GET Request
        given()
            .auth().preemptive().basic("postman", "password")
        .when()
            .get("/basic-auth")
        .then()
            .statusCode(200)
            .body("authenticated", equalTo(true))
            .log().all();
    }
}

Output:

{
  "authenticated": true
}

Explanation:

Line	Purpose
.auth().preemptive().basic(...)	Sends credentials proactively without waiting for a challenge
.get("/basic-auth")	Executes the GET request
.statusCode(200)	Asserts the response status is OK
.body("authenticated", equalTo(true))	Asserts that authentication was successful
.log().all()	Logs full response details to console