rest-api.php

<?php

// endpoints

function getToken() {
  echo 'GET token';
}

function postToken() {
  echo 'POST token';
}

//routing

router([
  'GET:auth/token' => 'getToken',
  'POST:auth/token' => 'postToken'
]);

// framework

function router($routes) {
  foreach ($routes as $rule => $func) {
    $parts = explode(':', $rule);
    if (
      count($parts) == 2
      && $_SERVER['REQUEST_METHOD'] == $parts[0]
      && preg_match('/' . addcslashes($parts[1], '/') . '/i', $_SERVER['REQUEST_URI'])
    ) {
      if (function_exists($func)) {
        return $func();
      } else {
        throw new Exception("Function $func doesn't exists", 1);
      }
    }
  }
  echo 'Endpoint "' . $_SERVER['REQUEST_METHOD'] . ' ' . $_SERVER['REQUEST_URI'] . '" not found';
}