What are the best practices for handling form submissions and user authentication in PHP to prevent errors like "Headers already been sent"?

When handling form submissions and user authentication in PHP, it is important to ensure that no output is sent to the browser before setting headers. To prevent errors like "Headers already sent", you should avoid any whitespace or HTML content before calling functions like header() or session_start(). 

<?php
ob_start(); // Start output buffering

// Your PHP code for handling form submissions and user authentication here

ob_end_flush(); // Flush the output buffer
?>

Keywords

PHP form submissions user authentication headers already sent error prevention

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