Add support for spring.rabbitmq.ssl.algorithm

Rabbit client 3.6.* uses TLSv1.1 as the default algorithm which
many brokers are deisabling these days. Spring AMQP supports
changing the algorithm by name, so this is just a pass thru for
that.

Author: Dave Syer

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/amqp/RabbitAutoConfiguration.java

@@ -119,6 +119,9 @@ public CachingConnectionFactory rabbitConnectionFactory(RabbitProperties config)
 			RabbitProperties.Ssl ssl = config.getSsl();
 			if (ssl.isEnabled()) {
 				factory.setUseSSL(true);
+				if (ssl.getAlgorithm() != null) {
+					factory.setSslAlgorithm(ssl.getAlgorithm());
+				}
 				factory.setKeyStore(ssl.getKeyStore());
 				factory.setKeyStorePassphrase(ssl.getKeyStorePassword());
 				factory.setTrustStore(ssl.getTrustStore());

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/amqp/RabbitProperties.java

@@ -217,6 +217,12 @@ public static class Ssl {
 		 */
 		private String trustStorePassword;
 
+		/**
+		 * The SSL algorithm to use (e.g. TLSv1.1). Default is set automatically by the
+		 * rabbit client library.
+		 */
+		private String algorithm;
+
 		public boolean isEnabled() {
 			return this.enabled;
 		}
@@ -257,6 +263,14 @@ public void setTrustStorePassword(String trustStorePassword) {
 			this.trustStorePassword = trustStorePassword;
 		}
 
+		public String getAlgorithm() {
+			return this.algorithm;
+		}
+
+		public void setAlgorithm(String sslAlgorithm) {
+			this.algorithm = sslAlgorithm;
+		}
+
 	}
 
 	public static class Listener {