What are the implications of allowing leading and trailing spaces in a validated username in PHP?

Allowing leading and trailing spaces in a validated username can lead to confusion and inconsistencies in the system. To solve this issue, you can trim the username input before validating it to remove any leading or trailing spaces. 

// Trim the username input before validating
$username = trim($_POST['username']);

// Validate the trimmed username
if (preg_match('/^[a-zA-Z0-9]{4,}$/', $username)) {
    // Username is valid
} else {
    // Username is invalid
}

Keywords

PHP username validation leading spaces trailing spaces implications

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