Lowercase the parsed options names

CHANGES.rst

@@ -9,7 +9,9 @@ Version 2.2.0
 -   Fix compatibility with Python 3.11 by ensuring that ``end_lineno``
     and ``end_col_offset`` are present on AST nodes. :issue:`2425`
 -   Add a new faster matching router based on a state
-    machine. :pr:`2433`.
+    machine. :pr:`2433`
+-   Names within options headers are always converted to lowercase. This
+    matches :rfc:`6266` that the case is not relevant. :issue:`2442`
 
 
 Version 2.1.2

src/werkzeug/http.py

@@ -390,6 +390,9 @@ def parse_options_header(
 
     :param value: The header value to parse.
 
+    .. versionchanged:: 2.2
+        Option names are always converted to lowercase.
+
     .. versionchanged:: 2.1
         The ``multiple`` parameter is deprecated and will be removed in
         Werkzeug 2.2.
@@ -440,7 +443,7 @@ def parse_options_header(
                 if not encoding:
                     encoding = continued_encoding
                 continued_encoding = encoding
-            option = unquote_header_value(option)
+            option = unquote_header_value(option).lower()
 
             if option_value is not None:
                 option_value = unquote_header_value(option_value, option == "filename")

tests/test_http.py

@@ -358,6 +358,10 @@ def test_parse_options_header_broken_values(self):
         assert http.parse_options_header(" , a ") == ("", {})
         assert http.parse_options_header(" ; a ") == ("", {})
 
+    def test_parse_options_header_case_insensitive(self):
+        _, options = http.parse_options_header(r'something; fileName="File.ext"')
+        assert options["filename"] == "File.ext"
+
     def test_dump_options_header(self):
         assert http.dump_options_header("foo", {"bar": 42}) == "foo; bar=42"
         assert http.dump_options_header("foo", {"bar": 42, "fizz": None}) in (