Force 'now' to be in UTC for signing requests

[JonathanFinch-awin]

Our server is running in Europe/London, at 26 OCT 2025 UTC 00:01:00, we had a load of errors for 1 hour:

AsyncAws\Core\Exception\Http\ClientException: HTTP 403 returned for "https://sqs.eu-west-1.amazonaws.com/".

Code:    InvalidSignatureException
Message: Signature not yet current: 20251026T010057Z is still later than 20251026T001557Z (20251026T000057Z + 15 min.)

We understand the culprit to be at these lines:

aws/src/Core/src/Signer/SignerV4.php

Lines 76 to 79 in 87fd89e

	$now = $context->getCurrentDate() ?? new \DateTimeImmutable();
	// Signer date have to be UTC https://docs.aws.amazon.com/general/latest/gr/sigv4-date-handling.html
	$now = $now->setTimezone(new \DateTimeZone('UTC'));

At 26 OCT 2025 UTC 00:01:00, on a server set to Europe/London, DateTimeImmutable yields:

$date = new DateTimeImmutable();
var_dump($date);
class DateTimeImmutable#1 (3) {
  public $date =>
  string(26) "2025-10-26 01:01:03.078020"
  public $timezone_type =>
  int(3)
  public $timezone =>
  string(13) "Europe/London"
}

Then when the timezone is updated as seen in the code:

$updated = $date->setTimezone(new \DateTimeZone('UTC'));
var_dump($updated);
class DateTimeImmutable#3 (3) {
  public $date =>
  string(26) "2025-10-26 01:01:03.078020"
  public $timezone_type =>
  int(3)
  public $timezone =>
  string(3) "UTC"
}

The time is inconsistent with the real UTC time at that given moment, hence the error.

If we force the instantiation of the date to include UTC which is covered in this PR, at 26 OCT 2025 UTC 00:01:00 the DateTime is instantiated as expected.

$dateUtc = new DateTimeImmutable('now', new DateTimeZone('UTC'));
var_dump($dateUtc);
class DateTimeImmutable#2 (3) {
  public $date =>
  string(26) "2025-10-26 00:01:03.078122"
  public $timezone_type =>
  int(3)
  public $timezone =>
  string(3) "UTC"
}

Then if the timezone is set to UTC, as seen in the code, it has no effect.

$updated = $dateUtc->setTimezone(new \DateTimeZone('UTC'));
var_dump($updated);
class DateTimeImmutable#5 (3) {
  public $date =>
  string(26) "2025-10-26 00:01:03.078122"
  public $timezone_type =>
  int(3)
  public $timezone =>
  string(3) "UTC"
}

We believe this would prevent the error. Unfortunately, as this relies on the system time being modified, it is very difficult to set up a unit test case to prove this behaviour.

Closes #1658

[stof]

Indeed. The root cause of the issue being that 2025-10-26 01:01:03.078020 Europe/London is ambiguous time due to the DST change.

[stof]

Please add the changelog entry for this fix

[JonathanFinch-awin]

Please add the changelog entry for this fix

Done. Thanks 👍

[stof]

I suggest document that as Fix signing request during DST change instead. The changelog should explain what user-visible we fixed, not how we fixed it (if they care about the implementation of the fix, they can look at the diff of the commit)

[JonathanFinch-awin]

Yep, good point, I've updated it and updated the commit message.