Load a secret from Azure Key Vault in a Spring Boot application

مقالة
04/06/2023

This tutorial shows you how to use Key Vault in Spring Boot applications to secure sensitive configuration data and retrieve configuration properties from Key Vault. Key Vault provides secure storage of generic secrets, such as passwords and database connection strings.

Prerequisites

An Azure subscription - create one for free.
Java Development Kit (JDK) version 8 or higher.
Apache Maven
Azure CLI
A Key Vault instance. If you don't have one, see Quickstart: Create a key vault using the Azure portal. Also, make a note of the URI of the Key Vault instance, as you need it for the test application for this tutorial.
A Spring Boot application. If you don't have one, create a Maven project with the Spring Initializr. Be sure to select Maven Project and, under Dependencies, add the Spring Web, Spring Data JPA, and H2 Database dependencies, and then select Java version 8 or higher.

Important

Spring Boot version 2.5 or higher is required to complete the steps in this article.

Set a secret to Azure Key Vault

This tutorial describes how to read database credentials from Key Vault in a Spring Boot application. To read the credentials from Key Vault, you should first store database credentials in Key Vault.

To store the URL of an H2 database as a new secret in Key Vault, see Quickstart: Set and retrieve a secret from Azure Key Vault using the Azure portal. In this tutorial, you'll set a secret with name h2url and value jdbc:h2:~/testdb;user=sa;password=password.

Note

After setting the secret, grant your app access to Key Vault by following the instructions in Assign a Key Vault access policy.

Read a secret from Azure Key Vault

Now that database credentials have been stored in Key Vault, you can retrieve them with Spring Cloud Azure.

To install the Spring Cloud Azure Key Vault Starter module, add the following dependencies to your pom.xml file:

The Spring Cloud Azure Bill of Materials (BOM):
```
<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>com.azure.spring</groupId>
      <artifactId>spring-cloud-azure-dependencies</artifactId>
      <version>5.17.1</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>
```
Note

If you're using Spring Boot 2.x, be sure to set the spring-cloud-azure-dependencies version to 4.19.0. This Bill of Material (BOM) should be configured in the <dependencyManagement> section of your pom.xml file. This ensures that all Spring Cloud Azure dependencies are using the same version. For more information about the version used for this BOM, see Which Version of Spring Cloud Azure Should I Use.

The Spring Cloud Azure Key Vault Starter artifact:

<dependency>
  <groupId>com.azure.spring</groupId>
  <artifactId>spring-cloud-azure-starter-keyvault</artifactId>
</dependency>

Spring Cloud Azure has several methods for reading secrets from Key Vault. You can use the following methods independently or combine them for different use cases:

Use Azure SDK for Key Vault.
Use Spring KeyVault PropertySource.

Use Azure SDK for Key Vault

Azure SDK for Key Vault provides SecretClient to manage secrets in Key Vault.

The following code example will show you how to use SecretClient to retrieve H2 database credentials from Azure Key Vault.

To read a secret using Azure SDK from Key Vault, configure the application by following these steps:

Configure a Key Vault endpoint in the application.properties configuration file.

spring.cloud.azure.keyvault.secret.endpoint=https://<your-keyvault-name>.vault.azure.net/

Inject the SecretClient bean in your Spring application and use the getSecret method to retrieve a secret, as shown in the following example:
```
import com.azure.security.keyvault.secrets.SecretClient;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SecretClientApplication implements CommandLineRunner {

    // Spring Cloud Azure will automatically inject SecretClient in your ApplicationContext.
    private final SecretClient secretClient;

    public SecretClientApplication(SecretClient secretClient) {
        this.secretClient = secretClient;
    }

    public static void main(String[] args) {
        SpringApplication.run(SecretClientApplication.class, args);
    }

    @Override
    public void run(String... args) {
        System.out.println("h2url: " + secretClient.getSecret("h2url").getValue());
    }
}
```
Tip

In this tutorial, there are no authentication operations in the configurations or the code. However, connecting to Azure services requires authentication. To complete the authentication, you need to use Azure Identity. Spring Cloud Azure uses DefaultAzureCredential, which the Azure Identity library provides to help you get credentials without any code changes.

DefaultAzureCredential supports multiple authentication methods and determines which method to use at runtime. This approach enables your app to use different authentication methods in different environments (such as local and production environments) without implementing environment-specific code. For more information, see DefaultAzureCredential.

To complete the authentication in local development environments, you can use Azure CLI, Visual Studio Code, PowerShell, or other methods. For more information, see Azure authentication in Java development environments. To complete the authentication in Azure hosting environments, we recommend using user-assigned managed identity. For more information, see What are managed identities for Azure resources?
Start the application. You'll see logs similar to the following example:
```
h2url: jdbc:h2:~/testdb;user=sa;password=password
```

You can build the SecretClient bean by yourself, but the process is complicated. In Spring Boot applications, you have to manage properties, learn the builder pattern, and register the client to your Spring application context. The following code example shows how you build a SecretClient bean:

import com.azure.identity.DefaultAzureCredentialBuilder;
import com.azure.security.keyvault.secrets.SecretClient;
import com.azure.security.keyvault.secrets.SecretClientBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class SecretClientConfiguration {

    @Bean
    public SecretClient createSecretClient() {
        return new SecretClientBuilder()
            .vaultUrl("https://<your-key-vault-url>.vault.azure.net/")
            .credential(new DefaultAzureCredentialBuilder().build())
            .buildClient();
    }

}

The following list shows some of the reasons why this code isn't flexible or graceful:

The Key Vault endpoint is hard coded.
If you use @Value to get configurations from the Spring environment, you can't have IDE hints in your application.properties file.
If you have a microservice scenario, the code must be duplicated in each project, and it's easy to make mistakes and hard to be consistent.

Fortunately, building the SecretClient bean by yourself isn't necessary with Spring Cloud Azure. Instead, you can directly inject SecretClient and use the configuration properties that you're already familiar with to configure Key Vault. For more information, see Configuration examples.

Spring Cloud Azure also provides the following global configurations for different scenarios. For more information, see the Global configuration for Azure Service SDKs section of the Spring Cloud Azure developer guide.

Proxy options.
Retry options.
HTTP transport client options.

You can also connect to different Azure clouds. For more information, see Connect to different Azure clouds.

Use Spring Key Vault PropertySource

The previous sections showed you how to use SecretClient in the CommandLineRunner to read the secret after the application started. In Spring Boot applications, however, reading secrets is required before the application starts. For example, the datasource password property is required before the application starts. The previous scenario won't work if you want to store the datasource password in Key Vault and still use the Spring auto-configuration to get a datasource.

In this case, Spring Cloud Azure provides Spring environment integration to load secrets from Key Vault before building the application context. You can use the secret to construct and configure the bean during Spring application context initialization. This approach is a transparent way for you to access secrets from Key Vault, and no code changes are required.

The following code example shows you how to use PropertySource to retrieve H2 database credentials to build the datasource from Azure Key Vault.

To retrieve the URL of an H2 database from Key Vault and store data from the H2 database using Spring Data JPA, configure the application by following these steps:

Add the following Key Vault endpoint and datasource properties to the application.properties configuration file.
```
logging.level.org.hibernate.SQL=DEBUG

spring.cloud.azure.keyvault.secret.property-sources[0].endpoint=https://<your-keyvault-name>.vault.azure.net/
spring.datasource.url=${h2url}

spring.jpa.hibernate.ddl-auto=create-drop
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
```
Tip

For examples of Spring Cloud Azure property configuration, see the Configuration examples section of the Spring Cloud Azure developer guide.

Tip

This example is a simple database scenario using an H2 database. We recommend using Azure Database for MySQL or Azure Database for PostgreSQL in a production environment and storing database URL, user name, and password in Azure Key Vault. If you want to avoid the password, passwordless connections is a good choice. For more information, see Passwordless connections for Azure services.

Create a new Todo Java class. This class is a domain model mapped onto the todo table that will be automatically created by JPA. The following code ignores the getters and setters methods.

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class Todo {

    public Todo() {
    }

    public Todo(String description, String details, boolean done) {
        this.description = description;
        this.details = details;
        this.done = done;
    }

    @Id
    @GeneratedValue
    private Long id;

    private String description;

    private String details;

    private boolean done;

}

Edit the startup class file to show the following content.

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.event.ApplicationReadyEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.Bean;
import org.springframework.data.jpa.repository.JpaRepository;

import java.util.stream.Stream;

@SpringBootApplication
public class KeyvaultApplication {

    public static void main(String[] args) {
        SpringApplication.run(KeyvaultApplication.class, args);
    }

    @Bean
    ApplicationListener<ApplicationReadyEvent> basicsApplicationListener(TodoRepository repository) {
        return event->repository
            .saveAll(Stream.of("A", "B", "C").map(name->new Todo("configuration", "congratulations, you have set up "
                + "correctly!", true)).toList())
            .forEach(System.out::println);
    }

}

interface TodoRepository extends JpaRepository<Todo, Long> {

}

Start the application. The application will retrieve the URL of the H2 database from Key Vault, then connect to the H2 database, and store data to the database. You'll see logs similar to the following example:
```
2023-01-13 15:51:35.498 DEBUG 5616 --- [main] org.hibernate.SQL: insert into todo (description, details, done, id) values (?, ?, ?, ?)
com.contoso.keyvault.Todo@1f
```

Deploy to Azure Spring Apps

Now that you have the Spring Boot application running locally, it's time to move it to production. Azure Spring Apps makes it easy to deploy Spring Boot applications to Azure without any code changes. The service manages the infrastructure of Spring applications so developers can focus on their code. Azure Spring Apps provides lifecycle management using comprehensive monitoring and diagnostics, configuration management, service discovery, CI/CD integration, blue-green deployments, and more. To deploy your application to Azure Spring Apps, see Deploy your first application to Azure Spring Apps.

Next steps

Azure for Spring developers Spring Cloud Azure KeyVault Samples

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