Add factory methods to create an SslManagerBundle from trust managers

Add two methods to create an SslManagerBundle from a given
TrustManagerFactory or from a single or multiple TrustManagers.

Both those methods use the default KeyManagerFactory.

Closes gh-43064

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/ssl/FixedTrustManagerFactory.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2012-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.ssl;
+
+import java.security.KeyStore;
+import java.security.Provider;
+
+import javax.net.ssl.ManagerFactoryParameters;
+import javax.net.ssl.TrustManager;
+import javax.net.ssl.TrustManagerFactory;
+import javax.net.ssl.TrustManagerFactorySpi;
+
+import org.springframework.boot.SpringBootVersion;
+
+/**
+ * {@link TrustManagerFactory} which uses a fixed set of {@link TrustManager
+ * TrustManagers}.
+ *
+ * @author Moritz Halbritter
+ */
+final class FixedTrustManagerFactory extends TrustManagerFactory {
+
+	private static final Provider PROVIDER = new Provider("FixedTrustManagerFactory", SpringBootVersion.getVersion(),
+			"") {
+	};
+
+	private FixedTrustManagerFactory(FixedTrustManagersSpi spi, String algorithm) {
+		super(spi, PROVIDER, algorithm);
+	}
+
+	static FixedTrustManagerFactory of(TrustManagerFactory trustManagerFactory, TrustManager... trustManagers) {
+		return new FixedTrustManagerFactory(new FixedTrustManagersSpi(trustManagers),
+				trustManagerFactory.getAlgorithm());
+	}
+
+	private static final class FixedTrustManagersSpi extends TrustManagerFactorySpi {
+
+		private final TrustManager[] trustManagers;
+
+		private FixedTrustManagersSpi(TrustManager[] trustManagers) {
+			this.trustManagers = trustManagers;
+		}
+
+		@Override
+		protected void engineInit(KeyStore ks) {
+		}
+
+		@Override
+		protected void engineInit(ManagerFactoryParameters spec) {
+		}
+
+		@Override
+		protected TrustManager[] engineGetTrustManagers() {
+			return this.trustManagers;
+		}
+
+	}
+
+}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/ssl/SslManagerBundle.java

@@ -16,6 +16,11 @@
 
 package org.springframework.boot.ssl;
 
+import java.security.KeyStore;
+import java.security.KeyStoreException;
+import java.security.NoSuchAlgorithmException;
+import java.security.UnrecoverableKeyException;
+
 import javax.net.ssl.KeyManager;
 import javax.net.ssl.KeyManagerFactory;
 import javax.net.ssl.SSLContext;
@@ -30,6 +35,7 @@ import org.springframework.util.Assert;
  * {@link SslStoreBundle}.
  *
  * @author Scott Frederick
+ * @author Moritz Halbritter
  * @since 3.1.0
  * @see SslStoreBundle
  * @see SslBundle#getManagers()
@@ -118,4 +124,59 @@ public interface SslManagerBundle {
 		return new DefaultSslManagerBundle(storeBundle, key);
 	}
 
+	/**
+	 * Factory method to create a new {@link SslManagerBundle} using the given
+	 * {@link TrustManagerFactory} and the default {@link KeyManagerFactory}.
+	 * @param trustManagerFactory the trust manager factory
+	 * @return a new {@link SslManagerBundle} instance
+	 * @since 3.5.0
+	 */
+	static SslManagerBundle from(TrustManagerFactory trustManagerFactory) {
+		Assert.notNull(trustManagerFactory, "TrustManagerFactory must not be null");
+		KeyManagerFactory defaultKeyManagerFactory = createDefaultKeyManagerFactory();
+		return of(defaultKeyManagerFactory, trustManagerFactory);
+	}
+
+	/**
+	 * Factory method to create a new {@link SslManagerBundle} using the given
+	 * {@link TrustManager TrustManagers} and the default {@link KeyManagerFactory}.
+	 * @param trustManagers the trust managers to use
+	 * @return a new {@link SslManagerBundle} instance
+	 * @since 3.5.0
+	 */
+	static SslManagerBundle from(TrustManager... trustManagers) {
+		Assert.notNull(trustManagers, "TrustManagers must not be null");
+		KeyManagerFactory defaultKeyManagerFactory = createDefaultKeyManagerFactory();
+		TrustManagerFactory defaultTrustManagerFactory = createDefaultTrustManagerFactory();
+		return of(defaultKeyManagerFactory, FixedTrustManagerFactory.of(defaultTrustManagerFactory, trustManagers));
+	}
+
+	private static TrustManagerFactory createDefaultTrustManagerFactory() {
+		String defaultAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
+		TrustManagerFactory trustManagerFactory;
+		try {
+			trustManagerFactory = TrustManagerFactory.getInstance(defaultAlgorithm);
+			trustManagerFactory.init((KeyStore) null);
+		}
+		catch (NoSuchAlgorithmException | KeyStoreException ex) {
+			throw new IllegalStateException(
+					"Unable to create TrustManagerFactory for default '%s' algorithm".formatted(defaultAlgorithm), ex);
+		}
+		return trustManagerFactory;
+	}
+
+	private static KeyManagerFactory createDefaultKeyManagerFactory() {
+		String defaultAlgorithm = KeyManagerFactory.getDefaultAlgorithm();
+		KeyManagerFactory keyManagerFactory;
+		try {
+			keyManagerFactory = KeyManagerFactory.getInstance(defaultAlgorithm);
+			keyManagerFactory.init(null, null);
+		}
+		catch (NoSuchAlgorithmException | KeyStoreException | UnrecoverableKeyException ex) {
+			throw new IllegalStateException(
+					"Unable to create KeyManagerFactory for default '%s' algorithm".formatted(defaultAlgorithm), ex);
+		}
+		return keyManagerFactory;
+	}
+
 }

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/ssl/FixedTrustManagerFactoryTests.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2012-2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.ssl;
+
+import java.security.NoSuchAlgorithmException;
+
+import javax.net.ssl.TrustManager;
+import javax.net.ssl.TrustManagerFactory;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+
+/**
+ * Tests for {@link FixedTrustManagerFactory}.
+ *
+ * @author Moritz Halbritter
+ */
+class FixedTrustManagerFactoryTests {
+
+	@Test
+	void shouldReturnTrustmanagers() throws Exception {
+		TrustManager trustManager1 = mock(TrustManager.class);
+		TrustManager trustManager2 = mock(TrustManager.class);
+		FixedTrustManagerFactory factory = FixedTrustManagerFactory.of(getDefaultTrustManagerFactory(), trustManager1,
+				trustManager2);
+		assertThat(factory.getTrustManagers()).containsExactly(trustManager1, trustManager2);
+	}
+
+	private static TrustManagerFactory getDefaultTrustManagerFactory() throws NoSuchAlgorithmException {
+		return TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
+	}
+
+}

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/ssl/SslManagerBundleTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.ssl;
 
 import javax.net.ssl.KeyManagerFactory;
 import javax.net.ssl.SSLContext;
+import javax.net.ssl.TrustManager;
 import javax.net.ssl.TrustManagerFactory;
 
 import org.junit.jupiter.api.Test;
@@ -31,12 +32,13 @@ import static org.mockito.Mockito.mock;
  * Tests for {@link SslManagerBundle}.
  *
  * @author Phillip Webb
+ * @author Moritz Halbritter
  */
 class SslManagerBundleTests {
 
-	private KeyManagerFactory keyManagerFactory = mock(KeyManagerFactory.class);
+	private final KeyManagerFactory keyManagerFactory = mock(KeyManagerFactory.class);
 
-	private TrustManagerFactory trustManagerFactory = mock(TrustManagerFactory.class);
+	private final TrustManagerFactory trustManagerFactory = mock(TrustManagerFactory.class);
 
 	@Test
 	void getKeyManagersDelegatesToFactory() {
@@ -85,4 +87,20 @@ class SslManagerBundleTests {
 		assertThat(bundle).isInstanceOf(DefaultSslManagerBundle.class);
 	}
 
+	@Test
+	void shouldReturnTrustManagerFactory() {
+		SslManagerBundle bundle = SslManagerBundle.from(this.trustManagerFactory);
+		assertThat(bundle.getKeyManagerFactory()).isNotNull();
+		assertThat(bundle.getTrustManagerFactory()).isSameAs(this.trustManagerFactory);
+	}
+
+	@Test
+	void shouldReturnTrustManagers() {
+		TrustManager trustManager1 = mock(TrustManager.class);
+		TrustManager trustManager2 = mock(TrustManager.class);
+		SslManagerBundle bundle = SslManagerBundle.from(trustManager1, trustManager2);
+		assertThat(bundle.getKeyManagerFactory()).isNotNull();
+		assertThat(bundle.getTrustManagerFactory().getTrustManagers()).containsExactly(trustManager1, trustManager2);
+	}
+
 }