PHP Passing Variables Between Pages and Security

i'm passing session and hidden variables between pages. not to mention
post values.

i'm a little concerned that someone with sufficient knowledge could
spoof these vlaues and manipulate the program.

is this a valid concern? i'm thinking i can check the submitting page
setting up something around the following the following code...

$base_name = basename($_SERVER['PHP_SELF']);

is this a good bet? is there a better way?

tia...

ps - posted this on php.general and, after 2 days w/o a response,
realized that probably wasn't the best place to post it.

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