Auto-configure SpringSecurityDialect for v5 and deprecate v4

Closes gh-14828

Author: wilkinsona

spring-boot-project/spring-boot-autoconfigure/pom.xml

@@ -623,6 +623,11 @@
 			<artifactId>thymeleaf-extras-springsecurity4</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.thymeleaf.extras</groupId>
+			<artifactId>thymeleaf-extras-springsecurity5</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>javax.jms</groupId>
 			<artifactId>javax.jms-api</artifactId>

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thymeleaf/ThymeleafAutoConfiguration.java

@@ -327,14 +327,34 @@ public DataAttributeDialect dialect() {
 	@ConditionalOnClass({ SpringSecurityDialect.class })
 	protected static class ThymeleafSecurityDialectConfiguration {
 
+		private final Log logger = LogFactory
+				.getLog(ThymeleafSecurityDialectConfiguration.class);
+
 		@Bean
 		@ConditionalOnMissingBean
 		public SpringSecurityDialect securityDialect() {
+			if (this.logger.isWarnEnabled()) {
+				this.logger.warn("Auto-configuration for thymeleaf-extras-springsecurity4"
+						+ " is deprecated in favour of thymeleaf-extras-springsecurity5");
+			}
 			return new SpringSecurityDialect();
 		}
 
 	}
 
+	@Configuration
+	@ConditionalOnClass({
+			org.thymeleaf.extras.springsecurity5.dialect.SpringSecurityDialect.class })
+	protected static class ThymeleafSecurity5DialectConfiguration {
+
+		@Bean
+		@ConditionalOnMissingBean
+		public org.thymeleaf.extras.springsecurity5.dialect.SpringSecurityDialect securityDialect() {
+			return new org.thymeleaf.extras.springsecurity5.dialect.SpringSecurityDialect();
+		}
+
+	}
+
 	@Configuration
 	@ConditionalOnClass(Java8TimeDialect.class)
 	protected static class ThymeleafJava8TimeDialect {

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -172,7 +172,9 @@
 		<statsd-client.version>3.1.0</statsd-client.version>
 		<sun-mail.version>${javax-mail.version}</sun-mail.version>
 		<thymeleaf.version>3.0.10.RELEASE</thymeleaf.version>
+		<!-- Deprecated in favour of thymeleaf-extras-springsecurity.version -->
 		<thymeleaf-extras-springsecurity4.version>3.0.3.RELEASE</thymeleaf-extras-springsecurity4.version>
+		<thymeleaf-extras-springsecurity.version>${thymeleaf-extras-springsecurity4.version}</thymeleaf-extras-springsecurity.version>
 		<thymeleaf-layout-dialect.version>2.3.0</thymeleaf-layout-dialect.version>
 		<thymeleaf-extras-data-attribute.version>2.0.1</thymeleaf-extras-data-attribute.version>
 		<thymeleaf-extras-java8time.version>3.0.1.RELEASE</thymeleaf-extras-java8time.version>
@@ -2951,7 +2953,12 @@
 			<dependency>
 				<groupId>org.thymeleaf.extras</groupId>
 				<artifactId>thymeleaf-extras-springsecurity4</artifactId>
-				<version>${thymeleaf-extras-springsecurity4.version}</version>
+				<version>${thymeleaf-extras-springsecurity.version}</version>
+			</dependency>
+			<dependency>
+				<groupId>org.thymeleaf.extras</groupId>
+				<artifactId>thymeleaf-extras-springsecurity5</artifactId>
+				<version>${thymeleaf-extras-springsecurity.version}</version>
 			</dependency>
 			<dependency>
 				<groupId>org.webjars</groupId>