Why isn't my Azure SAS Token Signature matching? - php

Question

This is the error returned when I try to access a blob in storage:
Code: AuthenticationFailed
Message: Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.
AuthenticationErrorDetail: Signature did not match. String to sign used was xxstorageaccount rwdlac b sco 2017-08-17T21:29:24Z 2017-08-17T21:34:24Z https 2017-04-17
Here's my code:
$storageAccount = config('azure.storage.account');
$start = new \DateTime();
$end = (new \DateTime())->modify('+5 minutes');
$start = $start->format('Y-m-d\TH:i:s\Z');
$end = $end->format('Y-m-d\TH:i:s\Z');
$toSign = $storageAccount . "\n";
$toSign .= "rwdlac" . "\n";
$toSign .= "b" . "\n";
$toSign .= "sco" . "\n";
$toSign .= $start . "\n";
$toSign .= $end . "\n";
$toSign .= "\n";
$toSign .= "https" . "\n";
$toSign .= "2017-04-17" . "\n";
$signature = rawurlencode(base64_encode(hash_hmac('sha256', $toSign, $sasKeyValue, TRUE)));
$token = "?sv=2017-04-17&ss=b&srt=sco&sp=rwdlac&se=" . $end . "&st=" . $start . "&spr=https&sig=" . $signature;
return $uri . $token;

Answer 1

You could do 2 things to avoid this error.
Convert start and end time to GMT time via setTimezone() function or consider using the gmdate function instead.
Decode base64 account key through base64_decode() function.
Please change your code like the following:
$storageAccount = config('azure.storage.account');
$start = (new \DateTime())->setTimezone(new DateTimeZone('GMT'));
$end = (new \DateTime())->setTimezone(new DateTimeZone('GMT'))->modify('+5 minutes');
$start = $start->format('Y-m-d\TH:i:s\Z');
$end = $end->format('Y-m-d\TH:i:s\Z');
$toSign = $storageAccount . "\n";
$toSign .= "rwdlac" . "\n";
$toSign .= "b" . "\n";
$toSign .= "sco" . "\n";
$toSign .= $start . "\n";
$toSign .= $end . "\n";
$toSign .= "\n";
$toSign .= "https" . "\n";
$toSign .= "2017-04-17" . "\n";
$signature = rawurlencode(base64_encode(hash_hmac('sha256', $toSign, base64_decode($sasKeyValue), TRUE)));
$token = "?sv=2017-04-17&ss=b&srt=sco&sp=rwdlac&se=" . $end . "&st=" . $start . "&spr=https&sig=" . $signature;
return $uri . $token;