#8 revert short list syntax

The short list-syntax breaks the test when getHeader() returns only
one element but with a non-zero index.

Author: BreiteSeite

src/BasicAccess.php

@@ -58,7 +58,7 @@ public function authenticate(ServerRequestInterface $request) : ?UserInterface
             return null;
         }
 
-        [$authHeader] = $authHeaders;
+        $authHeader = array_shift($authHeaders);
 
         if (! preg_match('/Basic (?P<credentials>.+)/', $authHeader, $match)) {
             return null;

test/BasicAccessTest.php

@@ -176,6 +176,13 @@ public function provideValidAuthentication(): array
     {
         return [
             'aladdin' => ['Aladdin', 'OpenSesame', ['Basic ' . base64_encode('Aladdin:OpenSesame')]],
+            'aladdin-with-nonzero-array-index' => [
+                'Aladdin',
+                'OpenSesame',
+                [
+                    -200 => 'Basic ' . base64_encode('Aladdin:OpenSesame')
+                ]
+            ],
             'passwords-with-colon' => ['Aladdin', 'Open:Sesame', ['Basic ' . base64_encode('Aladdin:Open:Sesame')]],
             'username-without-password' => ['Aladdin', '', ['Basic ' . base64_encode('Aladdin:')]],
             'password-without-username' => ['', 'OpenSesame', ['Basic ' . base64_encode(':OpenSesame')]],