Check if the openssl_sign went OK

[melroy89]

In case openssl_sign fails the $signature will be null. Resulting into errors like this:

{"message":"Warning: openssl_sign(): Supplied key param cannot be coerced into a private key","context":{"exception":{"class":"ErrorException","message":"Warning: openssl_sign(): Supplied key param cannot be coerced into a private key","code":0,"file":"/var/www/kbin.melroy.org/html/src/Service/ActivityPub/ApHttpClient.php:504"}},"level":400,"level_name":"ERROR","channel":"php","datetime":"2024-09-09T21:33:35.100575+02:00","extra":{}}
{"message":"Error thrown while handling message App\\Message\\ActivityPub\\Outbox\\DeliverMessage. Sending for retry #2 using 3600000 ms delay. Error: \"Handling \"App\\Message\\ActivityPub\\Outbox\\DeliverMessage\" failed: base64_encode(): Argument #1 ($string) must be of type string, null given\"","context":{"class":"App\\Message\\ActivityPub\\Outbox\\DeliverMessage","message_id":3420233,"retryCount":2,"delay":3600000,"error":"Handling \"App\\Message\\ActivityPub\\Outbox\\DeliverMessage\" failed: base64_encode(): Argument #1 ($string) must be of type string, null given","exception":{"class":"Symfony\\Component\\Messenger\\Exception\\HandlerFailedException","message":"Handling \"App\\Message\\ActivityPub\\Outbox\\DeliverMessage\" failed: base64_encode(): Argument #1 ($string) must be of type string, null given","code":0,"file":"/var/www/kbin.melroy.org/html/vendor/symfony/messenger/Middleware/HandleMessageMiddleware.php:124","previous":{"class":"TypeError","message":"base64_encode(): Argument #1 ($string) must be of type string, null given","code":0,"file":"/var/www/kbin.melroy.org/html/src/Service/ActivityPub/ApHttpClient.php:505"}}},"level":300,"level_name":"WARNING","channel":"messenger","datetime":"2024-09-09T21:33:35.100878+02:00","extra":{}}

We can better check on the return value of openssl_sign to validate if the signature actually succeeded or not.

If not, we now log a better error message. And we leave out the Signature header for now. We could also throw an error and abort. Ideas are welcome here.

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Also we now free the memory of the $key using the appropriate openssl_free_key method.