feat: Implement user invitation backend functionality

packages/backend/src/controllers/api/v1/users/accept-invitation.js

@@ -0,0 +1,23 @@
+import User from '../../../../models/user.js';
+
+export default async (request, response) => {
+  const { token, password } = request.body;
+
+  if (!token) {
+    throw new Error('Invitation token is required!');
+  }
+
+  const user = await User.query()
+    .findOne({ invitation_token: token })
+    .throwIfNotFound();
+
+  if (!user.isInvitationTokenValid()) {
+    throw new Error(
+      'Invitation link is not valid or expired. You can use reset password to get a new link.'
+    );
+  }
+
+  await user.acceptInvitation(password);
+
+  response.status(204).end();
+};