GH-2423 - Support Neo4j 4.4 user impersonation.

This change adds an API analogue to `DatabaseSelection` called `UserSelection`. The configuration and usage is identical to a dynamic database selection. It requires both Neo4j 4.4 server and database driver. To stay compatible with older driver version, we reflect over `withImpersonatedUser` inside `org.springframework.data.neo4j.core.transaction.Neo4jTransactionUtils`.

This closes #2423 and the linked PR #2422.

Author: michael-simons

src/main/asciidoc/faq/faq.adoc

@@ -326,6 +326,82 @@ public class Neo4jHealthConfig {
 }
 ----
 
+[[faq.impersonation]]
+== Neo4j 4.4 supports impersonation of different users - How can I use them?
+
+User impersonation is especially interesting in big multi-tenant settings, in which one physically connected (or technical)
+user can impersonate many tenants. Depending on your setup this will drastically reduce the number of physical driver instances needed.
+
+The feature requires Neo4j Enterprise 4.4+ on the server side and a 4.4+ driver on the client side (`org.neo4j.driver:neo4j-java-driver:4.4.0` or higher).
+
+For both imperative and reactive versions you need to provide a `UserSelectionProvider` respectively a `ReactiveUserSelectionProvider`.
+The same instance needs to be passed along to the `Neo4Client` and `Neo4jTransactionManager` respectively their reactive variants.
+
+In <<bootless-imperative-configuration,Bootless imperative>> and <<bootless-reactive-configuration, and reactive>> configurations you just need to provide a bean of the
+type in question:
+
+[[faq.impersonation.userselectionbean]]
+.User selection provider bean
+[source,java]
+----
+import org.springframework.data.neo4j.core.UserSelection;
+import org.springframework.data.neo4j.core.UserSelectionProvider;
+
+public class CustomConfig {
+
+    @Bean
+    public UserSelectionProvider getUserSelectionProvider() {
+        return () -> UserSelection.impersonate("someUser");
+    }
+}
+----
+
+In a typical Spring Boot scenario this feature requires a bit more work, as Boot supports also SDN versions without that feature.
+So given the bean in <<faq.impersonation.userselectionbean>>, you would need fully customize the client and transaction manager:
+
+[[faq.impersonation.boot]]
+.Necessary customization for Spring Boot
+[source,java]
+----
+import org.neo4j.driver.Driver;
+
+import org.springframework.data.neo4j.core.DatabaseSelectionProvider;
+import org.springframework.data.neo4j.core.Neo4jClient;
+import org.springframework.data.neo4j.core.UserSelectionProvider;
+import org.springframework.data.neo4j.core.transaction.Neo4jTransactionManager;
+
+import org.springframework.transaction.PlatformTransactionManager;
+
+public class CustomConfig {
+
+    @Bean
+    public Neo4jClient neo4jClient(
+        Driver driver,
+        DatabaseSelectionProvider databaseSelectionProvider,
+        UserSelectionProvider userSelectionProvider
+    ) {
+
+        return Neo4jClient.with(driver)
+            .withDatabaseSelectionProvider(databaseSelectionProvider)
+            .withUserSelectionProvider(userSelectionProvider)
+            .build();
+	}
+
+    @Bean
+    public PlatformTransactionManager transactionManager(
+        Driver driver,
+        DatabaseSelectionProvider databaseSelectionProvider,
+        UserSelectionProvider userSelectionProvider
+    ) {
+
+        return Neo4jTransactionManager
+            .with(driver)
+            .withDatabaseSelectionProvider(databaseSelectionProvider)
+            .withUserSelectionProvider(userSelectionProvider)
+            .build();
+	}
+}
+----
 
 [[faq.transactions.cluster]]
 == Do I need specific configuration so that transactions work seamless with a Neo4j Causal Cluster?

src/main/java/org/springframework/data/neo4j/config/AbstractNeo4jConfig.java

@@ -17,15 +17,19 @@
 
 import org.apiguardian.api.API;
 import org.neo4j.driver.Driver;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.data.neo4j.core.DatabaseSelectionProvider;
 import org.springframework.data.neo4j.core.Neo4jClient;
 import org.springframework.data.neo4j.core.Neo4jOperations;
 import org.springframework.data.neo4j.core.Neo4jTemplate;
+import org.springframework.data.neo4j.core.UserSelectionProvider;
 import org.springframework.data.neo4j.core.mapping.Neo4jMappingContext;
 import org.springframework.data.neo4j.core.transaction.Neo4jTransactionManager;
 import org.springframework.data.neo4j.repository.config.Neo4jRepositoryConfigurationExtension;
+import org.springframework.lang.Nullable;
 import org.springframework.transaction.PlatformTransactionManager;
 
 /**
@@ -40,6 +44,9 @@
 @API(status = API.Status.STABLE, since = "6.0")
 public abstract class AbstractNeo4jConfig extends Neo4jConfigurationSupport {
 
+	@Autowired
+	private ObjectProvider<UserSelectionProvider> userSelectionProviders;
+
 	/**
 	 * The driver to be used for interacting with Neo4j.
 	 *
@@ -55,7 +62,16 @@ public abstract class AbstractNeo4jConfig extends Neo4jConfigurationSupport {
 	 */
 	@Bean(Neo4jRepositoryConfigurationExtension.DEFAULT_NEO4J_CLIENT_BEAN_NAME)
 	public Neo4jClient neo4jClient(Driver driver, DatabaseSelectionProvider databaseSelectionProvider) {
-		return Neo4jClient.create(driver, databaseSelectionProvider);
+
+		return Neo4jClient.with(driver)
+				.withDatabaseSelectionProvider(databaseSelectionProvider)
+				.withUserSelectionProvider(getUserSelectionProvider())
+				.build();
+	}
+
+	@Nullable
+	private UserSelectionProvider getUserSelectionProvider() {
+		return this.userSelectionProviders == null ? null : this.userSelectionProviders.getIfUnique();
 	}
 
 	@Bean(Neo4jRepositoryConfigurationExtension.DEFAULT_NEO4J_TEMPLATE_BEAN_NAME)
@@ -68,17 +84,21 @@ public Neo4jOperations neo4jTemplate(final Neo4jClient neo4jClient, final Neo4jM
 	 * Provides a {@link PlatformTransactionManager} for Neo4j based on the driver resulting from {@link #driver()}.
 	 *
 	 * @param driver The driver to synchronize against
-	 * @param databaseNameProvider The configured database name provider
+	 * @param databaseSelectionProvider The configured database selection provider
 	 * @return A platform transaction manager
 	 */
 	@Bean(Neo4jRepositoryConfigurationExtension.DEFAULT_TRANSACTION_MANAGER_BEAN_NAME)
-	public PlatformTransactionManager transactionManager(Driver driver, DatabaseSelectionProvider databaseNameProvider) {
+	public PlatformTransactionManager transactionManager(Driver driver, DatabaseSelectionProvider databaseSelectionProvider) {
 
-		return new Neo4jTransactionManager(driver, databaseNameProvider);
+		return Neo4jTransactionManager
+				.with(driver)
+				.withDatabaseSelectionProvider(databaseSelectionProvider)
+				.withUserSelectionProvider(getUserSelectionProvider())
+				.build();
 	}
 
 	/**
-	 * Configures the database name provider.
+	 * Configures the database selection provider.
 	 *
 	 * @return The default database name provider, defaulting to the default database on Neo4j 4.0 and on no default on
 	 *         Neo4j 3.5 and prior.

src/main/java/org/springframework/data/neo4j/config/AbstractReactiveNeo4jConfig.java

@@ -17,14 +17,18 @@
 
 import org.apiguardian.api.API;
 import org.neo4j.driver.Driver;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.data.neo4j.core.ReactiveDatabaseSelectionProvider;
 import org.springframework.data.neo4j.core.ReactiveNeo4jClient;
 import org.springframework.data.neo4j.core.ReactiveNeo4jTemplate;
+import org.springframework.data.neo4j.core.ReactiveUserSelectionProvider;
 import org.springframework.data.neo4j.core.mapping.Neo4jMappingContext;
 import org.springframework.data.neo4j.core.transaction.ReactiveNeo4jTransactionManager;
 import org.springframework.data.neo4j.repository.config.ReactiveNeo4jRepositoryConfigurationExtension;
+import org.springframework.lang.Nullable;
 import org.springframework.transaction.PlatformTransactionManager;
 import org.springframework.transaction.ReactiveTransactionManager;
 
@@ -40,6 +44,9 @@
 @API(status = API.Status.STABLE, since = "6.0")
 public abstract class AbstractReactiveNeo4jConfig extends Neo4jConfigurationSupport {
 
+	@Autowired
+	private ObjectProvider<ReactiveUserSelectionProvider> userSelectionProviders;
+
 	/**
 	 * The driver to be used for interacting with Neo4j.
 	 *
@@ -54,8 +61,17 @@ public abstract class AbstractReactiveNeo4jConfig extends Neo4jConfigurationSupp
 	 * @return A reactive Neo4j client.
 	 */
 	@Bean(ReactiveNeo4jRepositoryConfigurationExtension.DEFAULT_NEO4J_CLIENT_BEAN_NAME)
-	public ReactiveNeo4jClient neo4jClient(Driver driver, ReactiveDatabaseSelectionProvider databaseNameProvider) {
-		return ReactiveNeo4jClient.create(driver, databaseNameProvider);
+	public ReactiveNeo4jClient neo4jClient(Driver driver, ReactiveDatabaseSelectionProvider databaseSelectionProvider) {
+
+		return ReactiveNeo4jClient.with(driver)
+				.withDatabaseSelectionProvider(databaseSelectionProvider)
+				.withUserSelectionProvider(getUserSelectionProvider())
+				.build();
+	}
+
+	@Nullable
+	private ReactiveUserSelectionProvider getUserSelectionProvider() {
+		return this.userSelectionProviders == null ? null : this.userSelectionProviders.getIfUnique();
 	}
 
 	@Bean(ReactiveNeo4jRepositoryConfigurationExtension.DEFAULT_NEO4J_TEMPLATE_BEAN_NAME)
@@ -73,9 +89,12 @@ public ReactiveNeo4jTemplate neo4jTemplate(final ReactiveNeo4jClient neo4jClient
 	 */
 	@Bean(ReactiveNeo4jRepositoryConfigurationExtension.DEFAULT_TRANSACTION_MANAGER_BEAN_NAME)
 	public ReactiveTransactionManager reactiveTransactionManager(Driver driver,
-			ReactiveDatabaseSelectionProvider databaseNameProvider) {
+			ReactiveDatabaseSelectionProvider databaseSelectionProvider) {
 
-		return new ReactiveNeo4jTransactionManager(driver, databaseNameProvider);
+		return ReactiveNeo4jTransactionManager.with(driver)
+				.withDatabaseSelectionProvider(databaseSelectionProvider)
+				.withUserSelectionProvider(getUserSelectionProvider())
+				.build();
 	}
 
 	/**

src/main/java/org/springframework/data/neo4j/core/DatabaseSelection.java

@@ -31,7 +31,7 @@
 @API(status = API.Status.STABLE, since = "6.0")
 public final class DatabaseSelection {
 
-	private final static DatabaseSelection DEFAULT_DATABASE_NAME = new DatabaseSelection(null);
+	private static final DatabaseSelection DEFAULT_DATABASE_NAME = new DatabaseSelection(null);
 
 	@Nullable private final String value;
 
@@ -51,7 +51,7 @@ public static DatabaseSelection byName(String databaseName) {
 		return new DatabaseSelection(databaseName);
 	}
 
-	private DatabaseSelection(String value) {
+	private DatabaseSelection(@Nullable String value) {
 		this.value = value;
 	}