fix(DeepL Node): Update credentials to use header-based authentication (#24614)

Co-authored-by: RomanDavydchuk <roman.davydchuk@n8n.io>

packages/nodes-base/credentials/DeepLApi.credentials.ts

@@ -41,8 +41,8 @@ export class DeepLApi implements ICredentialType {
 	authenticate: IAuthenticateGeneric = {
 		type: 'generic',
 		properties: {
-			qs: {
-				auth_key: '={{$credentials.apiKey}}',
+			headers: {
+				Authorization: '={{ "DeepL-Auth-Key " + $credentials.apiKey }}',
 			},
 		},
 	};

packages/nodes-base/credentials/test/DeepLApi.credentials.test.ts

@@ -0,0 +1,34 @@
+import { DeepLApi } from '../DeepLApi.credentials';
+
+describe('DeepLApi Credential', () => {
+	const deepLApi = new DeepLApi();
+
+	it('should have correct metadata and properties', () => {
+		expect(deepLApi.name).toBe('deepLApi');
+		expect(deepLApi.displayName).toBe('DeepL API');
+		expect(deepLApi.documentationUrl).toBe('deepl');
+		expect(deepLApi.properties).toHaveLength(2);
+		expect(deepLApi.properties[0].name).toBe('apiKey');
+		expect(deepLApi.properties[1].name).toBe('apiPlan');
+	});
+
+	it('should have correct test request configuration', () => {
+		expect(deepLApi.test.request.url).toBe('/usage');
+		expect(deepLApi.test.request.baseURL).toBe(
+			'={{$credentials.apiPlan === "pro" ? "https://api.deepl.com/v2" : "https://api-free.deepl.com/v2" }}',
+		);
+	});
+
+	describe('authenticate', () => {
+		it('should be configured for header-based authentication with correct format', () => {
+			const auth = deepLApi.authenticate as any;
+
+			expect(auth.type).toBe('generic');
+			expect(auth.properties.qs).toBeUndefined();
+			expect(auth.properties.headers).toBeDefined();
+			expect(auth.properties.headers.Authorization).toBe(
+				'={{ "DeepL-Auth-Key " + $credentials.apiKey }}',
+			);
+		});
+	});
+});