Google's PHP Quickstart adapted to use a service account

index.php

<?php

require_once __DIR__.'/vendor/autoload.php';

date_default_timezone_set('America/New_York');

define('SCOPES', implode(' ', array(
  Google_Service_Sheets::SPREADSHEETS_READONLY)
));

putenv('GOOGLE_APPLICATION_CREDENTIALS=SheetsV4Test-b8b1388db3d6.json');
$client = new Google_Client();
$client->useApplicationDefaultCredentials();
$client->setScopes(SCOPES);
$service = new Google_Service_Sheets($client);

// Prints the names and majors of students in a sample spreadsheet:
// https://docs.google.com/spreadsheets/d/1BxiMVs0XRA5nFMdKvBdBZjgmUUqptlbs74OgvE2upms/edit
$spreadsheetId = '1bqguOOiJMPm8HTR74TUx49WjGYIaiUQ7v_3PmNaoEGc';
$range = 'Class Data!A2:E';
$response = $service->spreadsheets_values->get($spreadsheetId, $range);
$values = $response->getValues();

if (count($values) == 0) {
  print "No data found.\n";
} else {
  print "Name, Major:\n";
  foreach ($values as $row) {
    // Print columns A and E, which correspond to indices 0 and 4.
    printf("%s, %s\n", $row[0], $row[4]);
  }
}

?>