Adding a duplicate README.md to the SDK directory

sdk/README.md

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+# XACML based authorization for Spring security
+
+### Overview
+
+Even though spring security provides role-based access control it doesn’t allow users to perform policy-based authorization. The main goal of this project is to write an agent which can be used to perform attribute-based access control for Spring security. 
+
+### Implementation
+
+Spring security provides an annotation for custom authorization evaluations.
+
+As the initial version, I have managed to write a working sample for this use case. This sample talks to WSO2 PDP for authorization.
+
+#### The high-level sequence diagram
+
+
+![](https://i.imgur.com/CUBbSxB.png)
+
+
+#### Usage
+
+1. Create a `keystore` and a `trustStore` in *Resources* directory.
+2. Create a file named `xacmlConfig.json` in *Resources* directory. This file contains the body of the XACML request.
+ * This file is a json file and this can have more than one *Target Domain Objects*. In this case let's define our target domain object as **admin_xacml**.
+ * All the variables should start with **'$'**. For example if **action-id** is the variable it should be defined in the `xacmlConfig.sjon` as **$action-id**.
+
+ A sample `xacmlConfig.json` file is as follows.
+ ````
+ {
+ "admin_xacml": {
+ "Request": {
+ "Action": {
+ "Attribute": [
+ {
+ "AttributeId": "urn:oasis:names:tc:xacml:1.0:action:action-id",
+ "Value": "$action-id"
+ }
+ ]
+ },
+ "Resource": {
+ "Attribute": [
+ {
+ "AttributeId": "urn:oasis:names:tc:xacml:1.0:resource:resource-id",
+ "Value": "$resource-id"
+ }
+ ]
+ }
+ }
+ }
+ }
+ ````
+  
+3. Define following properties in the `application.properties` file.
+ ```
+ xacml.pdp.url.authorize=https://localhost:9443/api/identity/entitlement/decision/pdp
+ xacml.pdp.url.resourceList=https://localhost:9443/api/identity/entitlement/decision/home
+ xacml.pdp.trustStore=truststore
+ xacml.pdp.trustStore.password=password
+ xacml.pdp.keyStore=keystore
+ xacml.pdp.keyStore.password=password
+ ``` 
+4. Extend `GlobalMethodSecurityConfiguration` class and set `AttributeEvaluator` as the new `PermissionEvaluator`
+ ```
+ @Configuration
+ @EnableGlobalMethodSecurity(prePostEnabled = true)
+ public class MethodSecurityConfig extends GlobalMethodSecurityConfiguration {
+ 
+ @Override
+ protected MethodSecurityExpressionHandler createExpressionHandler() {
+ 
+ DefaultMethodSecurityExpressionHandler expressionHandler =
+ new DefaultMethodSecurityExpressionHandler();
+ expressionHandler.setPermissionEvaluator(new AttributeEvaluator());
+ return expressionHandler;
+ }
+ }
+ ```
+5. Now add the `@PreAuthorize("hasPermission()")` or `@PostAuthorize("hasPermission()")` annotation as required before the correct controller method. *Target Domain Object* and the *Permissions* should be passed to this annotaion as parameters.*Permissions* is a json object which contains the key value pairs. These permission values will be extracted from the *headers*. 
+
+ ```
+ @PreAuthorize("hasPermission('admin_xacml','{$action-id:action-id,$resource-id:resource-id}')")
+ ```
+
+#### Note
+In addition to XACML Based Authorization, this SDK exposes methods to get `API Resource List` and `Entitled Attributes`.