client.php

<?php
/**
 * Class companiesHouseApi
 */
final class companiesHouseApi {

	const API_ENDPOINT = 'https://api.companieshouse.gov.uk';

	private $api_key = null;

	/**
	 * @param $api_key
	 */
	public function __construct($api_key) {
		if (!empty($api_key)) {
			$this->api_key = $api_key;
		} else {
			throw new InvalidArgumentException('Please supply a valid API key');
		}
	}

	/**
	 * @param string $endpoint
	 * @param array  $payload
	 *
	 * @return mixed
	 */
	public function send($endpoint, array $payload = []) {
		$ch = curl_init();
		curl_setopt($ch, CURLOPT_URL, $this->getRequestUrl($endpoint, $payload));
		curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
		curl_setopt($ch, CURLOPT_USERPWD, $this->api_key . ':');
		$result = curl_exec($ch);
		curl_close($ch);

		if ($json = json_decode($result, true)) {
			$result = $json;
		}

		return $result;
	}

	/**
	 * @param string $endpoint
	 * @param array  $payload
	 *
	 * @return string
	 */
	private function getRequestUrl($endpoint, array $payload) {
		$payload = array_merge($payload, ['ts' => time()]);
		$qs = '?' . http_build_query($payload);

		return self::API_ENDPOINT . $endpoint . $qs;
	}
}