Multiple Set-Cookie-Headers in Extbase-Responses are not sent to browser
If I add multiple HTTP-headers with the same name (e.g. "Set-Cookie") in Extbase-Controllers by adding them to the PSR-(Extbase-)Response, only the last one is sent to the browser.
The problem occurs in TYPO3\CMS\Extbase\Core\Bootstrap in line 202, when calling the header()-Method without making a difference if headers with multiple values should be replaced or added. Because of this behaviour, only the last Cookie is sent the the browser, because the last "Set-Cookie" overrides the previous one.
An identical problem existed in TYPO3 Core PSR-Responses, but was already fixed (see: https://forge.typo3.org/issues/88482).
This solution could also be adopted to Extbase to fix the described problem.