Updated README.md to include the authentication parameters and AWS_REGION

Author: ting-lan-wang

ojdbc-provider-aws/README.md

@@ -6,12 +6,16 @@ Amazon Web Services (AWS).
 ## Centralized Config Providers
 
 <dl>
-<dt><a href="#aws-config-config-provider">AWS S3 Configuration
+<dt><a href="#aws-s3-configuration-provider">AWS S3 Configuration
 Provider</a></dt>
 <dd>Provides connection properties managed by the S3 service</dd>
 <dt><a href="#aws-secrets-manager-config-provider">AWS Secrets Manager Configuration 
 Provider</a></dt>
 <dd>Provides connection properties managed by the Secrets Manager service</dd>
+<dt><a href="#common-parameters-for-centralized-config-providers">Common Parameters for Centralized Config Providers</a></dt>
+<dd>Common parameters supported by the config providers</dd>
+<dt><a href="#caching-configuration">Caching configuration</a></dt>
+<dd>Caching mechanism adopted by Centralized Config Providers</dd>
 </dl>
 
 Visit any of the links above to find information and usage examples for a
@@ -30,23 +34,7 @@ JDK versions. The coordinates for the latest release are:
 </dependency>
 ```
 
-## Authentication
-
-Providers use AWS SDK which supports
-[Default credentials provider chain](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/credentials-chain.html),
-which looks for credentials in a set of defined locations and use those
-credentials to authenticate requests to AWS.
-
-The default credentials provider chain searches for credentials in one of the following locations using a predefined sequence:
-
-1. Java system properties
-2. Environment variables
-3. Web identity token from AWS Security Token Service
-4. The shared credentials and config files
-5. Amazon ECS container credentials
-6. Amazon EC2 instance IAM role-provided credentials
-
-## AWS S3 Config Provider
+## AWS S3 Configuration Provider
 The Oracle DataSource uses a new prefix `jdbc:oracle:thin:@config-awss3:` to be able to identify that the configuration parameters should be loaded using AWS S3.
 Users only need to indicate the S3 URI of the object that contains the JSON payload.
 
@@ -85,8 +73,7 @@ And the JSON Payload for the file **payload_ojdbc_objectstorage.json** in **mybu
   "user": "scott",
   "password": { 
     "type": "awssecretsmanager",
-    "value": "test-secret",
-    "key_name": "db-password"
+    "value": "test-secret"
   },
   "jdbc": {
     "oracle.jdbc.ReadTimeout": 1000,
@@ -128,11 +115,6 @@ For the JSON type of provider (AWS S3, AWS Secrets Manager, HTTP/HTTPS, File) th
         - Base64 Encoded password (if base64)
         - GCP resource name (if gcpsecretmanager)
         - AWS Secret name (if awssecretsmanager)
-        - Text
-- key_name
-    - Optional
-    - Possible values
-        - Name of the key, if stored as key-value pairs in AWS Secrets Manager
 - authentication
     - Optional
     - Possible Values
@@ -148,6 +130,56 @@ jdbc:oracle:thin:@config-awssecretsmanager://{secret-name}
 
 The JSON Payload retrieved by AWS Secrets Manager Provider follows the same format in [AWS S3 Configuration Provider](#json-payload-format).
 
+## Common Parameters for Centralized Config Providers
+AWS S3 Configuration Provider and AWS Secrets Manager Configuration Provider
+share the same sets of parameters for authentication configuration.
+
+### Configuring Authentication
+
+The Centralized Config Providers in this module use the
+[Default credentials provider chain](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/credentials-chain.html) to provide authorization and authentication to S3 and Secrets Manager services.
+The user can provide an optional parameter `AUTHENTICATION` (case-ignored) which is mapped with the following Credential Class.
+
+<table>
+<thead><tr>
+<th>'AUTHENTICATION' Param Value</th>
+<th>Method</th>
+<th>Optional Configuration</th>
+<th>Optional Parameters</th>
+</tr></thead>
+<tbody>
+<tr>
+  <td><b>AWS_DEFAULT</b> or &lt;Empty&gt;</td>
+  <td>Default Credentials Provider Chain</td>
+  <td>see below Default Credentials Provider Chain</td>
+  <td>AWS_REGION (see AWS Region below)</td>
+</tr>
+</tbody>
+</table>
+
+### Default Credentials Provider Chain
+
+The default credentials provider chain provided by AWS SDK is implemented by the 
+[DefaultCredentialsProvider](https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/auth/credentials/DefaultCredentialsProvider.html) class,
+which searches for credentials in one of the following locations using a predefined sequence:
+
+1. Java system properties
+2. Environment variables
+3. Web identity token from AWS Security Token Service
+4. The shared credentials and config files
+5. Amazon ECS container credentials
+6. Amazon EC2 instance IAM role-provided credentials
+
+For more details, please refer to [Default credentials provider chain](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/credentials-chain.html).
+
+### AWS Region
+
+In this project, region can be specified from two places: 
+1. `AWS_REGION` as an optional parameter in URL
+2. [Default region provider chain](https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/region-selection.html#automatically-determine-the-aws-region-from-the-environment).
+
+If `AWS_REGION` is specified in the URL, the provider uses it as the value of Region for authentication. Otherwise, the value from default region provider chain will be applied.
+
 ## Caching configuration
 
 Config providers in this module store the configuration in caches to minimize