Configure max HTTP header size when using HTTP2 with Tomcat

Closes gh-31322

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizer.java

@@ -280,6 +280,11 @@ public class TomcatWebServerFactoryCustomizer
 			if (handler instanceof AbstractHttp11Protocol) {
 				AbstractHttp11Protocol protocol = (AbstractHttp11Protocol) handler;
 				protocol.setMaxHttpHeaderSize(maxHttpHeaderSize);
+				for (UpgradeProtocol upgradeProtocol : protocol.findUpgradeProtocols()) {
+					if (upgradeProtocol instanceof Http2Protocol) {
+						((Http2Protocol) upgradeProtocol).setMaxHeaderSize(maxHttpHeaderSize);
+					}
+				}
 			}
 		});
 	}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/embedded/TomcatWebServerFactoryCustomizerTests.java

@@ -182,6 +182,19 @@ class TomcatWebServerFactoryCustomizerTests {
 						.getMaxHttpHeaderSize()).isEqualTo(DataSize.ofKilobytes(1).toBytes()));
 	}
 
+	@Test
+	void customMaxHttpHeaderSizeWithHttp2() {
+		bind("server.max-http-header-size=1KB", "server.http2.enabled=true");
+		customizeAndRunServer((server) -> {
+			AbstractHttp11Protocol<?> protocolHandler = (AbstractHttp11Protocol<?>) server.getTomcat().getConnector()
+					.getProtocolHandler();
+			long expectedSize = DataSize.ofKilobytes(1).toBytes();
+			assertThat(protocolHandler.getMaxHttpHeaderSize()).isEqualTo(expectedSize);
+			assertThat(((Http2Protocol) protocolHandler.getUpgradeProtocol("h2c")).getMaxHeaderSize())
+					.isEqualTo(expectedSize);
+		});
+	}
+
 	@Test
 	void customMaxHttpHeaderSizeIgnoredIfNegative() {
 		bind("server.max-http-header-size=-1");