Readme doc on how to connect to Azure Managed Redis with Entra ID authentication (#3166)

* Readme doc on how to connect to Azure Managed Redis (AMR) and Azure Cache for Redis (ACR) with Entra ID authentication

* Spellcheck words list updated

* Formating

* Update docs/user-guide/connecting-redis.md

Co-authored-by: Tihomir Krasimirov Mateev <tihomir.mateev@redis.com>

* Apply suggestions from code review

Co-authored-by: Tihomir Krasimirov Mateev <tihomir.mateev@redis.com>

* Add section for Streaming Credentials

* Add section for Streaming Credentials - fix spell check

* Apply suggestions from code review

Co-authored-by: Tihomir Krasimirov Mateev <tihomir.mateev@redis.com>

---------

Co-authored-by: Tihomir Krasimirov Mateev <tihomir.mateev@redis.com>

Author: ggivo

.github/wordlist.txt

@@ -272,4 +272,9 @@ bom
 ubuntu
 behaviour
 databind
-jackson
+jackson
+ACR
+AMR
+Entra
+authx
+entraid

docs/user-guide/connecting-redis.md

@@ -237,3 +237,161 @@ RedisClient client = RedisClient.create(redisUri);
 client.shutdown();
 ```
 
+## Streaming Credentials Provider
+[Lettuce 6.6.0](https://github.com/redis/lettuce/releases/tag/6.6.0.RELEASE)  extends `RedisCredentialsProvider` to support streaming credentials. 
+It is useful when you need to refresh credentials periodically. Example use cases include: token expiration, rotating credentials, etc.
+Connection configured with `RedisCredentialsProvider` supporting streaming will be re-authenticated automatically when new credentials are emitted and `ReauthenticateBehavior` is set to `ON_NEW_CREDENTIALS`.
+
+### Step 1 - Create a Streaming Credentials Provider
+A simple example of a streaming credentials provider that emits new credentials.
+```java
+public class MyStreamingRedisCredentialsProvider implements RedisCredentialsProvider {
+
+    private final Sinks.Many<RedisCredentials> credentialsSink = Sinks.many().replay().latest();
+
+    @Override
+    public boolean supportsStreaming() {
+        return true;
+    }
+
+    @Override
+    public Mono<RedisCredentials> resolveCredentials() {
+        return credentialsSink.asFlux().next();
+    }
+    
+    @Override
+    // Provide a continuous stream of credentials
+    public Flux<RedisCredentials> credentials() {
+        return credentialsSink.asFlux().onBackpressureLatest(); 
+    }
+
+    public void close() {
+        credentialsSink.tryEmitComplete();
+    }
+    // Emit new credentials when needed
+    public void emitCredentials(String username, char[] password) {
+        credentialsSink.tryEmitNext(new StaticRedisCredentials(username, password));
+    }
+
+}
+```
+###  Step 2 - Create a RedisURI with streaming credentials provider
+
+```java
+    // Create a streaming credentials provider
+    MyStreamingRedisCredentialsProvider streamingCredentialsProvider = new MyStreamingRedisCredentialsProvider();
+    
+    // Emit initial credentials
+    streamingCredentialsProvider.emitCredentials("testuser", "testpass".toCharArray());
+   
+    // Enable automatic re-authentication
+    ClientOptions clientOptions = ClientOptions.builder()
+            // enable automatic re-authentication
+            .reauthenticateBehavior(ClientOptions.ReauthenticateBehavior.ON_NEW_CREDENTIALS)
+            .build();
+    
+    // Create a RedisURI with streaming credentials provider
+    RedisURI redisURI = RedisURI.builder().withHost(HOST).withPort(PORT)
+            .withAuthentication(streamingCredentialsProvider)
+            .build();
+    
+    // RedisClient
+    RedisClient redisClient = RedisClient.create(redisURI);
+    rediscClient.connect().sync().ping();
+    
+    // ...
+    // Emit new credentials when needed
+    streamingCredentialsProvider.emitCredentials("testuser", "password-rotated".toCharArray());
+    
+```
+
+## Microsoft Entra ID Authentication
+
+[Lettuce 6.6.0](https://github.com/redis/lettuce/releases/tag/6.6.0.RELEASE) introduces built-in support for authentication with [Azure Managed Redis](https://azure.microsoft.com/en-us/products/managed-redis) and Azure Cache for Redis using Microsoft Entra ID (formerly Azure Active Directory). It enables seamless integration with Azure's Redis services by fetching authentication tokens and managing the token renewal in the background. 
+Integration is built on top of [redis-authx](https://github.com/redis/jvm-redis-authx-entraid) library, and provides support for:
+
+ - System-assigned managed identity
+ - User-assigned managed identity
+ - Service principal
+
+You can learn more about managed identities in the [Microsoft Entra ID documentation](https://learn.microsoft.com/en-us/entra/identity/managed-identities-azure-resources/overview).
+
+### Basic Usage
+
+#### Pre-requisites
+* [register an application and create a service principal](https://learn.microsoft.com/en-us/entra/identity-platform/app-objects-and-service-principals?tabs=browser) in Azure.
+* Create a Redis cache in Azure and grant your service principal access: [AMR](https://learn.microsoft.com/en-us/azure/azure-cache-for-redis/managed-redis/managed-redis-entra-for-authentication) or [ACR](https://learn.microsoft.com/en-us/azure/azure-cache-for-redis/cache-azure-active-directory-for-authentication) documentation.
+ 
+#### Step 1 - Add the dependencies
+Lettuce requires [redis-authx-entraid](https://github.com/redis/jvm-redis-authx-entraid/) dependency to provide Microsoft Entra ID authentication support. Make sure to include that dependency on your classpath.
+
+If using Maven, add the following dependency to your `pom.xml`:
+
+``` xml
+        <dependency>
+            <groupId>redis.clients.authentication</groupId>
+            <artifactId>redis-authx-entraid</artifactId>
+            <version>0.1.1-beta1</version>
+        </dependency>
+```
+
+
+### Step 2 - Create Entra ID enabled credentials provider
+The lifecycle of the credentials provider is not managed by the Lettuce client. You can create it once and reuse it across multiple clients\connections. When no longer needed, you should close the provider to release resources `TokenBasedRedisCredentialsProvider#close`.
+
+#### Create Microsoft Entra ID enabled credentials provider
+```java
+  // Entra ID enabled credentials provider for Service Principle Identity with Client Secret
+  TokenBasedRedisCredentialsProvider credentialsSP;
+  try ( EntraIDTokenAuthConfigBuilder builder = EntraIDTokenAuthConfigBuilder.builder()) {
+       builder.clientId(CLIENT_ID)
+              .secret(CLIENT_SECRET)
+              .authority(AUTHORITY) // "https://login.microsoftonline.com/{YOUR_TENANT_ID}";
+              .scopes(SCOPES);      // "https://redis.azure.com/.default";
+      credentialsSP = TokenBasedRedisCredentialsProvider.create(builder.build());
+  }
+```
+
+You can test the credentials provider by obtaining a token.
+
+```java
+  // Test Entra ID credentials provider can resolve credentials
+  credentialsSP.resolveCredentials()
+      .doOnNext(c-> System.out.println(c.getUsername()))
+      .block();
+```
+
+### Step 3 - Enable automatic re-authentication
+Microsoft Entra ID tokens have a limited lifetime. Lettuce provides a mechanism to automatically re-authenticate when new credentials are emitted by a `RedisCredentialsProvider`.
+```java
+  // Enable automatic re-authentication
+  ClientOptions clientOptions = ClientOptions.builder()
+        .reauthenticateBehavior(ClientOptions.ReauthenticateBehavior.ON_NEW_CREDENTIALS)
+        .build();
+```
+
+### Step 4 - Connect with Entra ID enabled credentials provider
+
+```java
+  // Use Entra ID credentials provider
+  RedisURI redisURI = RedisURI.builder()
+      .withHost(HOST)
+      .withPort(PORT)
+      .withAuthentication(credentialsSP).build();
+
+  // RedisClient
+  RedisClient redisClient = RedisClient.create(redisURI1);
+  redisClient.setOptions(clientOptions);
+  
+  try {
+      redisClient.setOptions(clientOptions);
+      // Connect with Entra ID credentials provider
+      try (StatefulRedisConnection<String, String> user1 = redisClient.connect(StringCodec.UTF8)) {
+          System.out.println("Connected to redis as :" + user1.sync().aclWhoami());
+          System.out.println("Db size :" + user1.sync().dbsize());
+      }
+  } finally {
+      redisClient.shutdown();  // Shutdown Redis client and close connections
+      credentialsSP.close(); // Shutdown Entra ID Credentials provider
+  }
+```