Content-Disposition can parse BASE64 encoded filename

See gh-26463

spring-web/src/test/java/org/springframework/http/ContentDispositionTests.java

@@ -80,6 +80,18 @@ class ContentDispositionTests {
 						.build());
 	}
 
+	@Test
+	void parseBase64EncodedUTF8Filename() {
+		assertThat(parse("attachment; filename=\"=?UTF-8?B?5pel5pys6KqeLmNzdg==?=\"").getFilename())
+				.isEqualTo("日本語.csv");
+	}
+
+	@Test
+	void parseBase64EncodedShiftJISFilename() {
+		assertThat(parse("attachment; filename=\"=?SHIFT_JIS?B?k/qWe4zqLmNzdg==?=\"").getFilename())
+				.isEqualTo("日本語.csv");
+	}
+
 	@Test
 	void parseEncodedFilenameWithoutCharset() {
 		assertThat(parse("form-data; name=\"name\"; filename*=test.txt"))