Set authSource in MongoDB Docker Compose connection details

When authentication credentials are provided in environment variables
for the official MongoDB Docker image, the authentication source must
also be set to the `admin` database.

Fixes gh-35777

spring-boot-project/spring-boot-docker-compose/src/main/java/org/springframework/boot/docker/compose/service/connection/mongo/MongoDockerComposeConnectionDetailsFactory.java

@@ -30,6 +30,7 @@ import org.springframework.boot.docker.compose.service.connection.DockerComposeC
  * @author Moritz Halbritter
  * @author Andy Wilkinson
  * @author Phillip Webb
+ * @author Scott Frederick
  */
 class MongoDockerComposeConnectionDetailsFactory extends DockerComposeConnectionDetailsFactory<MongoConnectionDetails> {
 
@@ -73,6 +74,9 @@ class MongoDockerComposeConnectionDetailsFactory extends DockerComposeConnection
 			builder.append(service.ports().get(MONGODB_PORT));
 			builder.append("/");
 			builder.append((environment.getDatabase() != null) ? environment.getDatabase() : "test");
+			if (environment.getUsername() != null) {
+				builder.append("?authSource=admin");
+			}
 			return new ConnectionString(builder.toString());
 		}
 

spring-boot-project/spring-boot-docker-compose/src/test/java/org/springframework/boot/docker/compose/service/connection/mongo/MongoDockerComposeConnectionDetailsFactoryIntegrationTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.docker.compose.service.connection.mongo;
 
+import com.mongodb.ConnectionString;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.autoconfigure.mongo.MongoConnectionDetails;
@@ -29,6 +30,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Moritz Halbritter
  * @author Andy Wilkinson
  * @author Phillip Webb
+ * @author Scott Frederick
  */
 class MongoDockerComposeConnectionDetailsFactoryIntegrationTests extends AbstractDockerComposeIntegrationTests {
 
@@ -39,8 +41,11 @@ class MongoDockerComposeConnectionDetailsFactoryIntegrationTests extends Abstrac
 	@Test
 	void runCreatesConnectionDetails() {
 		MongoConnectionDetails connectionDetails = run(MongoConnectionDetails.class);
-		assertThat(connectionDetails.getConnectionString().toString()).startsWith("mongodb://root:secret@")
-			.endsWith("/mydatabase");
+		ConnectionString connectionString = connectionDetails.getConnectionString();
+		assertThat(connectionString.getCredential().getUserName()).isEqualTo("root");
+		assertThat(connectionString.getCredential().getPassword()).isEqualTo("secret".toCharArray());
+		assertThat(connectionString.getCredential().getSource()).isEqualTo("admin");
+		assertThat(connectionString.getDatabase()).isEqualTo("mydatabase");
 		assertThat(connectionDetails.getGridFs()).isNull();
 	}