WEB application data confidentiality and security discussion

Secret settings are not used by search engines to search for WEB applications. data confidentiality and security discussions
Most application systems are developed on the WEB. can you discuss the security of WEB application systems?
For example
In service middleware (Apache, etc.), set directory access control and enable https
The robots.txt setting created in the directory is not set by the search engine ....
...
I am a beginner in PHP. please give me more advice, especially in coding security. thank you.

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Php itself is okay. most of them are manual problems, depending on your work experience and your understanding of php.

All the questions you are talking about can be made manually, and they are irrelevant to the language itself.
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Learn a lot!
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Today, I have studied how unsafe it is to use cookies to store data,

However, user data is not stored locally and cannot be used for automatic logon. this is depressing.