Update Migration Assistant basic auth secret format documentation (#10186)

* Update MA secret format documentation

Signed-off-by: Tanner Lewis <lewijacn@amazon.com>

* Updates per PR feedback

Signed-off-by: Tanner Lewis <lewijacn@amazon.com>

* Apply suggestions from code review

Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Update getting-started-data-migration.md

Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Update _migration-assistant/deploying-migration-assistant/getting-started-data-migration.md

Signed-off-by: Nathan Bower <nbower@amazon.com>

---------

Signed-off-by: Tanner Lewis <lewijacn@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>
Signed-off-by: Nathan Bower <nbower@amazon.com>
Co-authored-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>
Co-authored-by: Nathan Bower <nbower@amazon.com>

Author: 3 people

_migration-assistant/deploying-migration-assistant/configuration-options.md

@@ -51,8 +51,7 @@ The following CDK performs a backfill migrations using RFS:
         "endpoint": <TARGET_CLUSTER_ENDPOINT>,
         "auth": {
             "type": "basic",
-            "username": <TARGET_CLUSTER_USERNAME>,
-            "passwordFromSecretArn": <TARGET_CLUSTER_PASSWORD_SECRET>
+            "userSecretArn": <SECRET_WITH_USERNAME_AND_PASSWORD_KEYS>
         }
     },
     "reindexFromSnapshotServiceEnabled": true,
@@ -93,8 +92,7 @@ The following sample CDK performs a live capture migration with C&R:
         "endpoint": <TARGET_CLUSTER_ENDPOINT>,
         "auth": {
             "type": "basic",
-            "username": <TARGET_CLUSTER_USERNAME>,
-            "passwordFromSecretArn": <TARGET_CLUSTER_PASSWORD_SECRET>
+            "userSecretArn": <SECRET_WITH_USERNAME_AND_PASSWORD_KEYS>
         }
     },
 
@@ -155,8 +153,7 @@ Both the source and target cluster can use no authentication, authentication lim
         "version": "ES 7.10",
         "auth": {
             "type": "basic",
-            "username": <TARGET_CLUSTER_USERNAME>,
-            "passwordFromSecretArn": <TARGET_CLUSTER_PASSWORD_SECRET>
+            "userSecretArn": <SECRET_WITH_USERNAME_AND_PASSWORD_KEYS>
         }
     }
 ```

_migration-assistant/deploying-migration-assistant/getting-started-data-migration.md

@@ -106,7 +106,14 @@ These commands deploy the following stacks:
 
 Use the following steps to configure and deploy RFS, deploy Migration Assistant, and verify installation of the required stacks:
 
-1. Add the source and target cluster password as separate **Secrets** in [AWS Secrets Manager](https://docs.aws.amazon.com/secretsmanager/latest/userguide/intro.html) as an unstructured string. Be sure to copy the secret Amazon Resource Name (ARN) for use during deployment.
+1. Add the basic authentication information (username and password) for both the source and target clusters as separate secrets in [AWS Secrets Manager](https://docs.aws.amazon.com/secretsmanager/latest/userguide/intro.html). Each secret must include two key-value pairs: one for the username and one for the password. The plaintext of each secret should resemble the following example:
+
+   ```json
+   {"username":"admin","password":"myStrongPassword123!"}
+   ```
+   
+   Be sure to copy the secret Amazon Resource Name (ARN) for use during deployment. 
+
 2. From the same shell as the Bootstrap instance, modify the `cdk.context.json` file located in the `/opensearch-migrations/deployment/cdk/opensearch-service-migration` directory and configure the following settings:
 
     ```json
@@ -118,17 +125,15 @@ Use the following steps to configure and deploy RFS, deploy Migration Assistant,
             "endpoint": "<TARGET CLUSTER ENDPOINT>",
             "auth": {
                 "type": "basic",
-                "username": "<TARGET CLUSTER USERNAME>",
-                "passwordFromSecretArn": "<TARGET CLUSTER PASSWORD SECRET>"
+                "userSecretArn": "<SECRET_WITH_USERNAME_AND_PASSWORD_KEYS>"
             }
         },
         "sourceCluster": {
             "endpoint": "<SOURCE CLUSTER ENDPOINT>",
             "version": "<SOURCE ENGINE VERSION>",
             "auth": {
                 "type": "basic",
-                "username": "<TARGET CLUSTER USERNAME>",
-                "passwordFromSecretArn": "<TARGET CLUSTER PASSWORD SECRET>"
+                "userSecretArn": "<SECRET_WITH_USERNAME_AND_PASSWORD_KEYS>"
             }
         },
         "reindexFromSnapshotExtraArgs": "<RFS PARAMETERS (see below)>",