feat(mailchimp): add mailchimp integration

packages/backend/src/apps/mailchimp/auth/generate-auth-url.js

@@ -0,0 +1,19 @@
+import { URLSearchParams } from 'url';
+
+export default async function generateAuthUrl($) {
+  const oauthRedirectUrlField = $.app.auth.fields.find(
+    (field) => field.key == 'oAuthRedirectUrl'
+  );
+  const redirectUri = oauthRedirectUrlField.value;
+  const searchParams = new URLSearchParams({
+    response_type: 'code',
+    client_id: $.auth.data.clientId,
+    redirect_uri: redirectUri,
+  });
+
+  const url = `https://login.mailchimp.com/oauth2/authorize?${searchParams.toString()}`;
+
+  await $.auth.set({
+    url,
+  });
+}