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                <?php  | 
            
                            
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                /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * Get an OAuth2 token from Google.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * * Install this script on your server so that it's accessible  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * as [https/http]://<yourdomain>/<folder>/get_oauth_token.php  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * e.g.: http://localhost/phpmail/get_oauth_token.php  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * * Ensure dependencies are installed with 'composer install'  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * * Set up an app in your Google developer console  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * * Set the script address as the app's redirect URL  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * If no refresh token is obtained when running this file, revoke access to your app  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * using link: https://accounts.google.com/b/0/IssuedAuthSubTokens and run the script again.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * This script requires PHP 5.4 or later  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * PHP Version 5.4  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                namespace League\OAuth2\Client\Provider;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                require 'vendor/autoload.php';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use League\OAuth2\Client\Provider\Exception\IdentityProviderException;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use League\OAuth2\Client\Token\AccessToken;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use League\OAuth2\Client\Tool\BearerAuthorizationTrait;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Psr\Http\Message\ResponseInterface;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                session_start();  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                //If this automatic URL doesn't work, set it yourself manually  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                $redirectUri = isset($_SERVER['HTTPS']) ? 'https://' : 'http://' . $_SERVER['HTTP_HOST'] . $_SERVER['PHP_SELF'];  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                //$redirectUri = 'http://localhost/phpmailer/get_oauth_token.php';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                //These details obtained are by setting up app in Google developer console.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                $clientId = 'RANDOMCHARS-----duv1n2.apps.googleusercontent.com';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                $clientSecret = 'RANDOMCHARS-----lGyjPcRtvP';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                class Google extends AbstractProvider  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    use BearerAuthorizationTrait;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    const ACCESS_TOKEN_RESOURCE_OWNER_ID = 'id';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @var string If set, this will be sent to google as the "access_type" parameter.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @link https://developers.google.com/accounts/docs/OAuth2WebServer#offline  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    protected $accessType;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @var string If set, this will be sent to google as the "hd" parameter.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @link https://developers.google.com/accounts/docs/OAuth2Login#hd-param  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    protected $hostedDomain;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @var string If set, this will be sent to google as the "scope" parameter.  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     * @link https://developers.google.com/gmail/api/auth/scopes  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                     */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    protected $scope;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function getBaseAuthorizationUrl()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return 'https://accounts.google.com/o/oauth2/auth';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function getBaseAccessTokenUrl(array $params)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return 'https://accounts.google.com/o/oauth2/token';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    public function getResourceOwnerDetailsUrl(AccessToken $token)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	return ' ';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                    protected function getAuthorizationParameters(array $options)  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    { | 
            
            
                                                                        
                            
            
                                    
            
            
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                	if (is_array($this->scope)) { | 
            
            
                                                                        
                            
            
                                    
            
            
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                            $separator = $this->getScopeSeparator();  | 
            
            
                                                                        
                            
            
                                    
            
            
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                            $this->scope = implode($separator, $this->scope);  | 
            
            
                                                                        
                            
            
                                    
            
            
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                        }  | 
            
            
                                                                        
                            
            
                                    
            
            
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                        $params = array_merge(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                            parent::getAuthorizationParameters($options),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                            array_filter([  | 
            
            
                                                                        
                            
            
                                    
            
            
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                                'hd'          => $this->hostedDomain,  | 
            
            
                                                                        
                            
            
                                    
            
            
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                                'access_type' => $this->accessType,  | 
            
            
                                                                        
                            
            
                                    
            
            
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                		'scope'       => $this->scope,  | 
            
            
                                                                        
                            
            
                                    
            
            
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                                // if the user is logged in with more than one account ask which one to use for the login!  | 
            
            
                                                                        
                            
            
                                    
            
            
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                                'authuser'    => '-1'  | 
            
            
                                                                        
                            
            
                                    
            
            
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                            ])  | 
            
            
                                                                        
                            
            
                                    
            
            
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                        );  | 
            
            
                                                                        
                            
            
                                    
            
            
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                        return $params;  | 
            
            
                                                                        
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    protected function getDefaultScopes()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return [  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'email',  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'openid',  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            'profile',  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        ];  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    protected function getScopeSeparator()  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return ' ';  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    protected function checkResponse(ResponseInterface $response, $data)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        if (!empty($data['error'])) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $code  = 0;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            $error = $data['error'];  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            if (is_array($error)) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                $code  = $error['code'];  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                                $error = $error['message'];  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                            throw new IdentityProviderException($error, $code, $data);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    protected function createResourceOwner(array $response, AccessToken $token)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        return new GoogleUser($response);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                }  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                //Set Redirect URI in Developer Console as [https/http]://<yourdomain>/<folder>/get_oauth_token.php  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                $provider = new Google(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                    array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                        'clientId' => $clientId,  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 | 
                                    
                                                     | 
                
                 | 
                        'clientSecret' => $clientSecret,  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    135
                 | 
                                    
                                                     | 
                
                 | 
                        'redirectUri' => $redirectUri,  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    136
                 | 
                                    
                                                     | 
                
                 | 
                        'scope' => array('https://mail.google.com/'), | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    137
                 | 
                                    
                                                     | 
                
                 | 
                	'accessType' => 'offline'  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    138
                 | 
                                    
                                                     | 
                
                 | 
                    )  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    139
                 | 
                                    
                                                     | 
                
                 | 
                );  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    140
                 | 
                                    
                                                     | 
                
                 | 
                 | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    141
                 | 
                                    
                                                     | 
                
                 | 
                if (!isset($_GET['code'])) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    142
                 | 
                                    
                                                     | 
                
                 | 
                    // If we don't have an authorization code then get one  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    143
                 | 
                                    
                                                     | 
                
                 | 
                    $authUrl = $provider->getAuthorizationUrl();  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    144
                 | 
                                    
                                                     | 
                
                 | 
                    $_SESSION['oauth2state'] = $provider->getState();  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    145
                 | 
                                    
                                                     | 
                
                 | 
                    header('Location: ' . $authUrl); | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    146
                 | 
                                    
                                                     | 
                
                 | 
                    exit;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    147
                 | 
                                    
                                                     | 
                
                 | 
                // Check given state against previously stored one to mitigate CSRF attack  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    148
                 | 
                                    
                                                     | 
                
                 | 
                } elseif (empty($_GET['state']) || ($_GET['state'] !== $_SESSION['oauth2state'])) { | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    149
                 | 
                                    
                                                     | 
                
                 | 
                    unset($_SESSION['oauth2state']);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    150
                 | 
                                    
                                                     | 
                
                 | 
                    exit('Invalid state'); | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    151
                 | 
                                    
                                                     | 
                
                 | 
                } else { | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    152
                 | 
                                    
                                                     | 
                
                 | 
                    // Try to get an access token (using the authorization code grant)  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    153
                 | 
                                    
                                                     | 
                
                 | 
                    $token = $provider->getAccessToken(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    154
                 | 
                                    
                                                     | 
                
                 | 
                        'authorization_code',  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    155
                 | 
                                    
                                                     | 
                
                 | 
                        array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    156
                 | 
                                    
                                                     | 
                
                 | 
                            'code' => $_GET['code']  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    157
                 | 
                                    
                                                     | 
                
                 | 
                        )  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    158
                 | 
                                    
                                                     | 
                
                 | 
                    );  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    159
                 | 
                                    
                                                     | 
                
                 | 
                 | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    160
                 | 
                                    
                                                     | 
                
                 | 
                    // Use this to get a new access token if the old one expires  | 
            
            
                                                                                                            
                            
            
                                    
            
            
                | 
                    161
                 | 
                                    
                                                     | 
                
                 | 
                    echo 'Refresh Token: ' . $token->getRefreshToken();  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
                | 
                    162
                 | 
                                    
                                                     | 
                
                 | 
                }  | 
            
            
                                                        
            
                                    
            
            
                | 
                    163
                 | 
                                    
                                                     | 
                
                 | 
                 | 
            
            
                        
The PSR-1: Basic Coding Standard recommends that a file should either introduce new symbols, that is classes, functions, constants or similar, or have side effects. Side effects are anything that executes logic, like for example printing output, changing ini settings or writing to a file.
The idea behind this recommendation is that merely auto-loading a class should not change the state of an application. It also promotes a cleaner style of programming and makes your code less prone to errors, because the logic is not spread out all over the place.
To learn more about the PSR-1, please see the PHP-FIG site on the PSR-1.