Objective-C WebKit框架从Facebook获取访问令牌

我在互联网上发现了一些信息，可以通过WebKit框架从Facebook获得访问令牌。这是真的吗？如果是，那么怎么做？

您可以将请求发布到Facebook API并获取有效的访问令牌，或者使用登录

-(NSString *)loadAccessToken{
    NSString *accessTokenURL = [NSString stringWithFormat:@"https://graph.facebook.com/oauth/access_token?client_id=%@&client_secret=%@&grant_type=client_credentials",client_id, client_secret];

    ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:[NSURL URLWithString:accessTokenURL]];  
    [request startSynchronous];

    NSMutableString *accessMutable = [[request responseString] mutableCopy];
    [accessMutable replaceOccurrencesOfString:@"access_token=" 
                               withString:@"" 
                                  options:NSLiteralSearch 
                                    range:NSMakeRange(0, [[request responseString] length])];

    return accessMutable;
}