scrapy有模拟登录网站的相关方法吗？

用scrapy写爬虫，模拟登录只能自己写？还是scrapy有模拟登录的相关方法？

下面是手册中的代码示例，不太懂：

import scrapy

class LoginSpider(scrapy.Spider):
    name = 'example.com'
    start_urls = ['http://www.example.com/users/login.php']
    
    def parse(self, response):
        return scrapy.FormRequest.from_response(
            response,
            formdata={'username': 'john', 'password': 'secret'},
            callback=self.after_login
        )
        
def after_login(self, response):
    # check login succeed before going on
    if "authentication failed" in response.body:
        self.logger.error("Login failed")
        return
        
    # continue scraping with authenticated session...

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初始化爬虫预先post到登陆接口，然后保持cookies