FacebookCanvasLoginHelper.fbmd

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# FacebookCanvasLoginHelper for the Facebook SDK for PHP

A helper class for getting a FacebookSession in a Canvas app
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## Facebook\FacebookCanvasLoginHelper {#overview}

If your app is loaded through Canvas, Facebook sends a POST request with a signed request.  This helper class will handle processing and validating that information with Facebook, and returns a `FacebookSession`.

Usage:

~~~~

$helper = new FacebookCanvasLoginHelper();
try {
  $session = $helper->getSession();
} catch (FacebookRequestException $ex) {
	// When Facebook returns an error
} catch (\Exception $ex) {
	// When validation fails or other local issues	
}
if ($session) {
  // Logged in.
}

~~~~
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## Instance Methods {#instance-methods}

### getSession {#getsession}
`getSession()`  
Processes the POST request from Facebook, if present.  Returns a `FacebookSession` or `null`.
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