How can we improve the security of Web code? -Php Tutorial

I just graduated from an Internet company and saw that the previous code has many security risks. for example, I can use ajax to send some requests to complete some operations. Is there any way to improve the security of my code? are there any books or tools that can be recommended? Thank you! I just graduated from an Internet company and saw that the previous code has many security risks. for example, I can use ajax to send some requests to complete some operations. Is there any way to improve the security of my code? are there any books or tools that can be recommended? Thank you! Reply content: recommended:
Advanced PHP application vulnerability review technology [https://code.google.com/p/pasc2at/wiki/SimplifiedChinese ]
Php Codz Hacking [http://www.80vul.com/pch/ ]
Some Of Discuz! Bugs [http://www.80vul.com/dzvul/ ]
80Vul [http://www.80vul.com/ ]
Wst bbs [http://www.phpsec.net/ ]
WooYun Zone [http://zone.wooyun.org/zone/php ] The existing answers are biased towards system backend security. I will provide a front-end development idea:

1. all operations involving data changes (add, delete, and modify) should use the POST method.
2. all user-input content should be escaped (esacpe)
3. in the head section of the HTML document, specify charset first (see http://code.google.com/p/doctype/wiki/ArticleUtf7 )
4. set the correct document. domain
5. if you rely on cookies to verify the logon status, make sure that cookies in the current domain are not contaminated (see Yummy cookies website SS domains website GitHub )
6. try not to use JavaScript to dynamically insert text controls (especially when binding events with onxxx, you can refer to the idea of AngularJS)

Supplement the WooYun knowledge base The more you know about web security, the more secure your code is. if you think of that knowledge when writing code... Every variable is confidential. Every input is harmful. XSS, SQL injection check, CSRF. For more information, see White hat Web security (Douban)