chore: sort headers alphabetically

.changes/nextrelease/chore-sort-presigned-headers.json

@@ -0,0 +1,7 @@
+[
+    {
+        "type": "enhancement",
+        "category": "",
+        "description": "Sorts presigned headers alphabetically."
+    }
+]

src/Signature/SignatureV4.php

@@ -155,6 +155,9 @@ private function getPresignHeaders(array $headers)
                 $presignHeaders[] = $lName;
             }
         }
+
+        sort($presignHeaders);
+
         return $presignHeaders;
     }
 

tests/Signature/SignatureV4Test.php

@@ -304,7 +304,7 @@ public function testPresignSpecificHeaders()
             'x-amz-content-sha256' => 'abc',
         ]);
         $presigned = $sig->presign($req, $creds, '+5 minutes');
-        $this->assertStringContainsString(urlencode('host;x-amz-foo;content-md5;x-amz-meta-foo'), (string)$presigned->getUri());
+        $this->assertStringContainsString(urlencode('content-md5;host;x-amz-foo;x-amz-meta-foo'), (string)$presigned->getUri());
     }
 
     public function testPresignBlacklistedHeaders()
@@ -613,4 +613,23 @@ public function testRemovesIllegalV4aHeadersBeforeSigning()
             $this->assertEquals($value, $req->getHeaderLine($key));
         }
     }
+
+    public function testSortHeadersAlphabetically()
+    {
+        $signature = new SignatureV4('foo', 'bar');
+        $credentials = new Credentials('a', 'b');
+        $headers = [
+            'z-header-1' => 'foo',
+            'x-header-2' => 'bar',
+            'b-header-3' => 'baz',
+            'a-header-3' => 'baz',
+            'r-header-4' => 'bar',
+        ];
+        $req = new Request('PUT', 'http://foo.com', $headers);
+        $presigned = $signature->presign($req, $credentials, '+5 minutes');
+        $this->assertStringContainsString(
+            urlencode('a-header-3;b-header-3;host;r-header-4;x-header-2;z-header-1'),
+            (string)$presigned->getUri()
+        );
+    }
 }