diff --git a/core/src/main/java/org/springframework/security/core/userdetails/UserDetailsPasswordService.java b/core/src/main/java/org/springframework/security/core/userdetails/UserDetailsPasswordService.java
new file mode 100644
index 0000000000..a282db973d
--- /dev/null
+++ b/core/src/main/java/org/springframework/security/core/userdetails/UserDetailsPasswordService.java
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2002-2018 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
+ *
+ *      http://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.security.core.userdetails;
+
+/**
+ * An API for changing a {@link UserDetails} password.
+ * @author Rob Winch
+ * @since 5.1
+ */
+public interface UserDetailsPasswordService {
+
+	/**
+	 * Modify the specified user's password. This should change the user's password in the
+	 * persistent user repository (datbase, LDAP etc).
+	 *
+	 * @param user the user to modify the password for
+	 * @param newPassword the password to change to
+	 * @return the updated UserDetails with the new password
+	 */
+	UserDetails updatePassword(UserDetails user, String newPassword);
+}
diff --git a/core/src/main/java/org/springframework/security/provisioning/InMemoryUserDetailsManager.java b/core/src/main/java/org/springframework/security/provisioning/InMemoryUserDetailsManager.java
index 6592d63b40..55c462cde4 100644
--- a/core/src/main/java/org/springframework/security/provisioning/InMemoryUserDetailsManager.java
+++ b/core/src/main/java/org/springframework/security/provisioning/InMemoryUserDetailsManager.java
@@ -30,6 +30,7 @@ import org.springframework.security.core.Authentication;
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.security.core.userdetails.User;
 import org.springframework.security.core.userdetails.UserDetails;
+import org.springframework.security.core.userdetails.UserDetailsPasswordService;
 import org.springframework.security.core.userdetails.UsernameNotFoundException;
 import org.springframework.security.core.userdetails.memory.UserAttribute;
 import org.springframework.security.core.userdetails.memory.UserAttributeEditor;
@@ -45,7 +46,8 @@ import org.springframework.util.Assert;
  * @author Luke Taylor
  * @since 3.1
  */
-public class InMemoryUserDetailsManager implements UserDetailsManager {
+public class InMemoryUserDetailsManager implements UserDetailsManager,
+		UserDetailsPasswordService {
 	protected final Log logger = LogFactory.getLog(getClass());
 
 	private final Map<String, MutableUserDetails> users = new HashMap<>();
@@ -138,6 +140,14 @@ public class InMemoryUserDetailsManager implements UserDetailsManager {
 		user.setPassword(newPassword);
 	}
 
+	@Override
+	public UserDetails updatePassword(UserDetails user, String newPassword) {
+		String username = user.getUsername();
+		MutableUserDetails mutableUser = this.users.get(username);
+		mutableUser.setPassword(newPassword);
+		return mutableUser;
+	}
+
 	public UserDetails loadUserByUsername(String username)
 			throws UsernameNotFoundException {
 		UserDetails user = users.get(username.toLowerCase());
diff --git a/core/src/test/java/org/springframework/security/provisioning/InMemoryUserDetailsManagerTests.java b/core/src/test/java/org/springframework/security/provisioning/InMemoryUserDetailsManagerTests.java
new file mode 100644
index 0000000000..9f58cc5385
--- /dev/null
+++ b/core/src/test/java/org/springframework/security/provisioning/InMemoryUserDetailsManagerTests.java
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2002-2018 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
+ *
+ *      http://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.security.provisioning;
+
+import org.junit.Test;
+import org.springframework.security.core.userdetails.PasswordEncodedUser;
+import org.springframework.security.core.userdetails.UserDetails;
+
+import static org.assertj.core.api.Assertions.*;
+
+/**
+ * @author Rob Winch
+ * @since 5.1
+ */
+public class InMemoryUserDetailsManagerTests {
+	private final UserDetails user = PasswordEncodedUser.user();
+
+	private InMemoryUserDetailsManager manager = new InMemoryUserDetailsManager(this.user);
+
+	@Test
+	public void changePassword() {
+		String newPassword = "newPassword";
+		this.manager.updatePassword(this.user, newPassword);
+		assertThat(this.manager.loadUserByUsername(this.user.getUsername()).getPassword()).isEqualTo(newPassword);
+	}
+}