PHP

php guzzle client x-www-form-urlencoded

$res = $client->post('http://example.co.uk/auth/token', [
    'form_params' => [
        'client_id' => 'SOMEID',
        'client_secret' => '9999jjjj67Y0LBLq8CbftgfdreehYEI=',
        'grant_type' => 'client_credentials'
    ]
]);