Add Partitioned cookie attribute support for servers

This commit adds support for the "Partitioned" cookie attribute in
WebFlux servers and the related testing infrastructure.
Note, Undertow does not support this feature at the moment.

Closes gh-31454

spring-test/src/test/java/org/springframework/mock/web/MockCookieTests.java

@@ -71,7 +71,7 @@ class MockCookieTests {
 	@Test
 	void parseHeaderWithAttributes() {
 		MockCookie cookie = MockCookie.parse("SESSION=123; Domain=example.com; Max-Age=60; " +
-				"Expires=Tue, 8 Oct 2019 19:50:00 GMT; Path=/; Secure; HttpOnly; SameSite=Lax");
+				"Expires=Tue, 8 Oct 2019 19:50:00 GMT; Path=/; Secure; HttpOnly; Partitioned; SameSite=Lax");
 
 		assertCookie(cookie, "SESSION", "123");
 		assertThat(cookie.getDomain()).isEqualTo("example.com");
@@ -79,6 +79,7 @@ class MockCookieTests {
 		assertThat(cookie.getPath()).isEqualTo("/");
 		assertThat(cookie.getSecure()).isTrue();
 		assertThat(cookie.isHttpOnly()).isTrue();
+		assertThat(cookie.isPartitioned()).isTrue();
 		assertThat(cookie.getExpires()).isEqualTo(ZonedDateTime.parse("Tue, 8 Oct 2019 19:50:00 GMT",
 				DateTimeFormatter.RFC_1123_DATE_TIME));
 		assertThat(cookie.getSameSite()).isEqualTo("Lax");
@@ -203,4 +204,12 @@ class MockCookieTests {
 		assertThatThrownBy(() -> cookie.setAttribute("expires", "12345")).isInstanceOf(DateTimeParseException.class);
 	}
 
+	@Test
+	void setPartitioned() {
+		MockCookie cookie = new MockCookie("SESSION", "123");
+		cookie.setAttribute("Partitioned", "");
+
+		assertThat(cookie.isPartitioned()).isTrue();
+	}
+
 }

spring-test/src/test/java/org/springframework/mock/web/MockHttpServletResponseTests.java

@@ -274,12 +274,13 @@ class MockHttpServletResponseTests {
 		cookie.setMaxAge(0);
 		cookie.setSecure(true);
 		cookie.setHttpOnly(true);
+		cookie.setAttribute("Partitioned", "");
 
 		response.addCookie(cookie);
 
 		assertThat(response.getHeader(SET_COOKIE)).isEqualTo(("foo=bar; Path=/path; Domain=example.com; " +
 				"Max-Age=0; Expires=Thu, 01 Jan 1970 00:00:00 GMT; " +
-				"Secure; HttpOnly"));
+				"Secure; HttpOnly; Partitioned"));
 	}
 
 	@Test

spring-test/src/test/java/org/springframework/test/web/reactive/server/CookieAssertionsTests.java

@@ -37,7 +37,7 @@ import static org.mockito.Mockito.mock;
  *
  * @author Rossen Stoyanchev
  */
-public class CookieAssertionTests {
+public class CookieAssertionsTests {
 
 	private final ResponseCookie cookie = ResponseCookie.from("foo", "bar")
 			.maxAge(Duration.ofMinutes(30))
@@ -45,6 +45,7 @@ public class CookieAssertionTests {
 			.path("/foo")
 			.secure(true)
 			.httpOnly(true)
+			.partitioned(true)
 			.sameSite("Lax")
 			.build();
 
@@ -117,6 +118,12 @@ public class CookieAssertionTests {
 		assertThatExceptionOfType(AssertionError.class).isThrownBy(() -> assertions.httpOnly("foo", false));
 	}
 
+	@Test
+	void partitioned() {
+		assertions.partitioned("foo", true);
+		assertThatExceptionOfType(AssertionError.class).isThrownBy(() -> assertions.partitioned("foo", false));
+	}
+
 	@Test
 	void sameSite() {
 		assertions.sameSite("foo", "Lax");