feat(Postmark Trigger Node): Update credentials so they can be used with the HTTP Request Node (#4790)

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

@@ -1,4 +1,9 @@
-import { ICredentialType, INodeProperties } from 'n8n-workflow';
+import {
+	IAuthenticateGeneric,
+	ICredentialTestRequest,
+	ICredentialType,
+	INodeProperties,
+} from 'n8n-workflow';
 
 export class PostmarkApi implements ICredentialType {
 	name = 'postmarkApi';
@@ -12,4 +17,19 @@ export class PostmarkApi implements ICredentialType {
 			default: '',
 		},
 	];
+	authenticate: IAuthenticateGeneric = {
+		type: 'generic',
+		properties: {
+			headers: {
+				'X-Postmark-Server-Token': '={{$credentials.serverToken}}',
+			},
+		},
+	};
+	test: ICredentialTestRequest = {
+		request: {
+			baseURL: 'https://api.postmarkapp.com',
+			url: '/server',
+			method: 'GET',
+		},
+	};
 }