Performing API Security Testing with Postman

When to Use

• Building repeatable API security test suites for OWASP API Security Top 10 coverage
• Creating automated security regression tests that run in CI/CD pipelines via Newman
• Testing API authentication and authorization across multiple user roles systematically
• Integrating Postman with OWASP ZAP proxy for combined manual and automated security testing
• Establishing a baseline security test collection for new API endpoints before deployment

Do not use against production APIs without authorization. Postman security testing involves sending potentially malicious payloads.

Prerequisites

• Postman Desktop or web application with an active workspace
• Target API with OpenAPI/Swagger specification for collection import
• Test accounts for at least three roles: unauthenticated, regular user, admin
• Newman CLI installed for CI/CD integration: npm install -g newman
• OWASP ZAP configured as local proxy (localhost:8080) for Postman proxy integration
• API environment variables for base URL, tokens, and test data

Workflow

Step 1: Environment and Collection Setup

Create Postman environments for multi-role testing:

// Environment: API Security Test - Regular User
{
    "values": [
        {"key": "base_url", "value": "https://target-api.example.com/api/v1"},
        {"key": "auth_token", "value": ""},
        {"key": "user_email", "value": "regular@test.com"},
        {"key": "user_password", "value": "TestPass123!"},
        {"key": "user_id", "value": ""},
        {"key": "other_user_id", "value": "1002"},
        {"key": "admin_endpoint", "value": "/admin/users"},
        {"key": "test_order_id", "value": ""},
        {"key": "other_user_order_id", "value": "5003"}
    ]
}

Pre-request script for automatic authentication:

// Collection-level pre-request script for auto-login
if (!pm.environment.get("auth_token") || pm.environment.get("token_expired")) {
    const loginRequest = {
        url: pm.environment.get("base_url") + "/auth/login",
        method: "POST",
        header: {"Content-Type": "application/json"},
        body: {
            mode: "raw",
            raw: JSON.stringify({
                email: pm.environment.get("user_email"),
                password: pm.environment.get("user_password")
            })
        }
    };

    pm.sendRequest(loginRequest, (err, res) => {
        if (!err && res.code === 200) {
            const token = res.json().access_token;
            pm.environment.set("auth_token", token);
            pm.environment.set("user_id", res.json().user.id);
        }
    });
}

Step 2: BOLA (API1) Test Collection

// Test: Access other user's profile (BOLA)
// Request: GET {{base_url}}/users/{{other_user_id}}
// Auth: Bearer {{auth_token}}

// Test script:
pm.test("BOLA: Cannot access other user profile", function() {
    pm.expect(pm.response.code).to.be.oneOf([401, 403]);
});

pm.test("BOLA: No user data leaked on denial", function() {
    if (pm.response.code === 200) {
        const body = pm.response.json();
        pm.expect(body).to.not.have.property("email");
        pm.expect(body).to.not.have.property("phone");
        pm.expect(body).to.not.have.property("address");
        // Flag as BOLA if full profile returned
        console.error("BOLA VULNERABILITY: Full profile returned for other user");
    }
});

// Test: Access other user's order
// Request: GET {{base_url}}/orders/{{other_user_order_id}}
pm.test("BOLA: Cannot access other user order", function() {
    pm.expect(pm.response.code).to.be.oneOf([401, 403, 404]);
});

// Test: Modify other user's resource
// Request: PATCH {{base_url}}/users/{{other_user_id}}
// Body: {"name": "Hacked"}
pm.test("BOLA: Cannot modify other user profile", function() {
    pm.expect(pm.response.code).to.be.oneOf([401, 403]);
});

Step 3: Authentication (API2) Test Collection

// Test: Token validation
// Request: GET {{base_url}}/users/me
// Auth: Bearer invalid_token_value

pm.test("Auth: Invalid token rejected", function() {
    pm.expect(pm.response.code).to.be.oneOf([401, 403]);
});

// Test: Expired token handling
// Request: GET {{base_url}}/users/me
// Auth: Bearer {{expired_token}}

pm.test("Auth: Expired token rejected", function() {
    pm.expect(pm.response.code).to.equal(401);
});

// Test: Missing authentication
// Request: GET {{base_url}}/users/me
// Auth: None


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