Laravel API: Best way to check if requested data exists

Hi,

I am writing some API endpoints to check activity for a specific user in a specific forum thread. I have 4 different endpoints that start with the same actions:

1. Check if the forum thread belongs to the authenticated user (this is the actual owner of the thread, not the user we are requesting the activity from).
2. Check if the requested user (the user for which we request the activity, not the authenticated user) is subscribed to the thread.

$thread = Thread::where('id', $id)
			->where('customer_id', auth()->user()->id)
			->first();

if (!$thread) return response()->json(['message' => 'Thread not found'], 422);

$user = UserLinked::where('thread_id', $id)
			->where('user_id', $userId)
			->first();

if (!$user) return response()->json(['message' => 'User not found'], 422);

I was thinking to create a FormRequest and check in the rules function (see below). But the parameters I am using are route parameters and not post parameters which causes the validation to give errors as 'id' and 'userId' are not found in post parameters.

public function rules()
	{
		$id = $this->route('id');
		$userId = $this->route('userId');
		$customerId = auth()->user()->id;

		return [
			'id' => [
				'required',
				Rule::exists('thread')->where(function ($query) use ($id, $customerId) {
					$query->where('id', $id)->where('customer_id', $customerId);
				}),
			],
			'userId' => [
				'required',
				Rule::exists('user_linked')->where(function ($query) use ($id, $userId) {
					$query->where('thread_id', $id)->where('user_id', $userId);
				}),
			],
		];
	}

I am a bit lost on how to handle this the best way to avoid code replication. Do I just write a function in my controller that checks for the validity? This will result in something like this which I don't like either..

if (!($thread = $this->threadFound($id)))
			return response()->json(['message' => 'Thread not found'], 422);

if (!($linked = $this->userFound($id, $userId)))
			return response()->json(['message' => 'User not found'], 422);

Any other suggestions on how to handle this the best and cleanest way?