Unable to proceed through OAuth2.0 - php

Question

I have generated tokens and code and everything and i am able to login and authorize the user but somehow I am getting error. Two error has been spotted.
First One
(
[error] => invalid_grant
[error_description] => Authorization code doesn't exist or is invalid for the client
)
Sometimes authorization code is not generating so I am getting above error. And sometimes when I am able to generate auth_code I am getting below error
{"error":"invalid_token","error_description":"The access token provided is invalid"}
I am developer of the site abcd.com and now I have a platform where I need to develop my abcd.com for that platform. To implement login I have to use OAuth2.0 and this is the requirement of the platform. I have read a lot of documents on OAuth2.0 and build the app. I am using codeigniter though.
server.php
$dsn = 'mysql:dbname=my_oauth2_db;host=localhost';
$username = 'root';
$password = '';
// error reporting (this is a demo, after all!)
ini_set('display_errors',1);error_reporting(E_ALL);
// Autoloading (composer is preferred, but for this example let's just do this)
require_once('oauth2-server-php/src/OAuth2/Autoloader.php');
OAuth2\Autoloader::register();
// $dsn is the Data Source Name for your database, for exmaple "mysql:dbname=my_oauth2_db;host=localhost"
$storage = new OAuth2\Storage\Pdo(array('dsn' => $dsn, 'username' => $username, 'password' => $password));
// Pass a storage object or array of storage objects to the OAuth2 server class
$server = new OAuth2\Server($storage);
// Add the "Client Credentials" grant type (it is the simplest of the grant types)
$server->addGrantType(new OAuth2\GrantType\ClientCredentials($storage));
// Add the "Authorization Code" grant type (this is where the oauth magic happens)
$server->addGrantType(new OAuth2\GrantType\AuthorizationCode($storage));
$scope = new OAuth2\Scope(array(
'supported_scopes' => array('email')
));
$server->setScopeUtil($scope);
Here is my authorize.php
require_once __DIR__.'/server.php';
$request = OAuth2\Request::createFromGlobals();
$client_id = $request->query['client_id'];
$response = new OAuth2\Response();
if (!$server->validateAuthorizeRequest($request, $response)) {
$response->send();
die;
}
if (empty($_POST)) {
exit('<form method="post">
<label>Do You Authorize '.$client_id.'?</label><br />
<input class="yes_authorize" type="submit" name="authorized" value="Yes">
<input class="no_authorize" type="submit" name="authorized" value="No">
</form>');
}
$is_authorized = ($_POST['authorized'] === 'Yes');
$server->handleAuthorizeRequest($request, $response, $is_authorized);
if ($is_authorized) {
$code = substr($response->getHttpHeader('Location'), strpos($response->getHttpHeader('Location'), 'code=')+5, 40);
$client_secret = $_GET['state'];
$token_value = shell_exec("curl -u CLIENT_ID:CLIENT_SECRET https://abcd.com/api/token.php -d 'grant_type=authorization_code&code=$code'");
$token = json_decode($token_value);
$access_token = $token->access_token;
$expires_in = $token->expires_in;
$state = $_GET['state'];
$resource_result = shell_exec("curl https://abcd.com/api/resource.php -d 'access_token=$code'");
$redirect_url = $_GET['redirecturi']."?code=$access_token&state=".$_GET['state'];
exit(header("location: $redirect_url"));
}
$response->send();
resource.php
require_once __DIR__.'/server.php';
if (!$server->verifyResourceRequest(OAuth2\Request::createFromGlobals())) {
$server->getResponse()->send();
die;
}
echo json_encode(array('success' => true, 'message' => 'You accessed my APIs!'));
token.php
require_once __DIR__.'/server.php';
$server->handleTokenRequest(OAuth2\Request::createFromGlobals())->send();
If you see authorize.php, After generating access_token through token.php, If I pass that to resource.php, I am getting second error. AND I have passed auth_code as well as access_token both to my redirect url, but I am getting not able to get through.