diff --git a/README.md b/README.md
index 47a3ccb..10b92ef 100644
--- a/README.md
+++ b/README.md
@@ -26,10 +26,19 @@ Typesafe access to [Testing Farm's REST API](https://api.dev.testing-farm.io/red
 ```typescript
 import TestingFarmAPI from "testing-farm";
 
+const api = new TestingFarmAPI("https://api.dev.testing-farm.io/v0.1", "api-key");
+
+// Passing api key in data - not recommended
 const api = new TestingFarmAPI("https://api.dev.testing-farm.io/v0.1");
+
 await api.about();
 ```
 
+> [!WARNING]
+>
+> Passing the API key in request body is deprecated and not recommended. It is better to pass it in the constructor.
+> This way the API key will be passed in the request header as part of `Authorization` header.
+
 ### List a Test Requests
 
 documentation of - [`GET /requests`](https://api.dev.testing-farm.io/redoc#operation/get_test_requests_v0_1_requests_get)
diff --git a/src/index.ts b/src/index.ts
index 9c1bf69..daa6042 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,4 +1,4 @@
-import { PublicLink } from './link';
+import { ApiKeyLink, PublicLink, TestingFarmLink } from './link';
 import { isError } from './util';
 import {
   About,
@@ -46,10 +46,15 @@ export {
 };
 
 export default class TestingFarmAPI {
-  private readonly link: PublicLink;
-
-  constructor(instance: string) {
-    this.link = new PublicLink(new URL(instance));
+  private readonly link: TestingFarmLink;
+
+  constructor(instance: string, apiKey?: string) {
+    // Use PublicLink only for endpoints that don't require authentication
+    if (!apiKey) {
+      this.link = new PublicLink(new URL(instance));
+    } else {
+      this.link = new ApiKeyLink(new URL(instance), apiKey);
+    }
   }
 
   async requests(filter: RequestsFilter): Promise<Request[]>;
diff --git a/src/link.ts b/src/link.ts
index a353aec..a722b87 100644
--- a/src/link.ts
+++ b/src/link.ts
@@ -97,3 +97,30 @@ export class PublicLink extends TestingFarmLink {
     return performRequest(config);
   }
 }
+
+/**
+ * Handles authentication using an API key.
+ */
+export class ApiKeyLink extends TestingFarmLink {
+  public constructor(
+    instance: URL,
+    private readonly apiKey: string
+  ) {
+    super(instance);
+  }
+
+  protected async request(config: AxiosRequestConfig): Promise<unknown> {
+    return performRequest({
+      ...config,
+      headers: {
+        ...(config.headers ?? {}),
+        // https://api.dev.testing-farm.io/redoc#operation/request_a_new_test_v0_1_requests_post
+        // OAuth2: OAuth2PasswordBearer
+        // The API key for authentication.
+        // Flow type: password
+        // Token URL: token
+        Authorization: `Bearer ${this.apiKey}`,
+      },
+    });
+  }
+}
diff --git a/src/schema.ts b/src/schema.ts
index ab186a7..55bb51c 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -135,7 +135,7 @@ export const requestsFilterSchema = z.object({
 export type RequestsFilter = z.infer<typeof requestsFilterSchema>;
 
 export const newRequestSchema = z.object({
-  api_key: z.any(),
+  api_key: z.any().optional(),
   test: testObjectSchema,
   environments: z.array(environmentSchema).optional(),
   notification: notificationSchema.optional().nullable(),
@@ -208,7 +208,7 @@ export const requestSchema = z.object({
 export type Request = z.infer<typeof requestSchema>;
 
 export const cancelRequestSchema = z.object({
-  api_key: z.any(),
+  api_key: z.any().optional(),
 });
 
 export type CancelRequest = z.infer<typeof cancelRequestSchema>;
diff --git a/test/integration/cancel-request.test.ts b/test/integration/cancel-request.test.ts
index 380080c..97cb8ff 100644
--- a/test/integration/cancel-request.test.ts
+++ b/test/integration/cancel-request.test.ts
@@ -14,11 +14,14 @@ describe('Test Testing Farm DELETE /requests/{request_id}', () => {
   });
 
   test.todo('unsafe response', async () => {
-    const api = new TestingFarmAPI('https://api.dev.testing-farm.io/v0.1');
+    const api = new TestingFarmAPI(
+      'https://api.dev.testing-farm.io/v0.1',
+      'api_key'
+    );
 
     const response = await api.cancelRequest(
       'f053796b-452e-4da2-b4e1-26eb2f3e721f',
-      { api_key: 'api_key' },
+      {},
       false
     );
     expect(response).toBeTypeOf('object');