Add Oauth client service

                 String msg = "Invalid tenant domain : " + tenantDomain;
                 return Response.status(Response.Status.NOT_ACCEPTABLE).entity(msg).build();
             }
+

-                    ApiApplicationConstants.DEFAULT_TOKEN_TYPE, username, false,
-                    ApiApplicationConstants.DEFAULT_VALIDITY_PERIOD, PrivilegedCarbonContext.getThreadLocalCarbonContext().getUserRealm()
-                            .getRealmConfiguration().getAdminPassword(), null, null, null, false);
+            ApiApplicationKey apiApplicationKey =

             if ((registrationProfile.getTags() != null && registrationProfile.getTags().length != 0)) {
-                if (!APIUtil.getAllowedApisTags().containsAll(Arrays.asList(registrationProfile.getTags()))) {
-                    return Response.status(Response.Status.NOT_ACCEPTABLE).entity("APIs(Tags) are not allowed to this user."
+                if (!new HashSet<>(APIUtil.getAllowedApisTags()).containsAll(Arrays.asList(registrationProfile.getTags()))) {

+            ApiApplicationKey apiApplicationKey =
+                    apiManagementProviderService.registerApiApplication(idnAuthenticationProfile,
+                            apiApplicationProfile);
+            return Response.status(Response.Status.CREATED).entity(apiApplicationKey).build();

+@Provider
+@Produces(APPLICATION_JSON)
+@Consumes(APPLICATION_JSON)
+public class GsonMessageBodyHandler implements MessageBodyWriter<Object>, MessageBodyReader<Object> {

+public class GsonMessageBodyHandler implements MessageBodyWriter<Object>, MessageBodyReader<Object> {
+
+    private Gson gson;
+    private static final String UTF_8 = "UTF-8";

     <context-param>
         <param-name>doAuthentication</param-name>
-        <param-value>true</param-value>
+        <param-value>false</param-value>

 	<context-param>
 		<param-name>basicAuth</param-name>
-		<param-value>true</param-value>
+		<param-value>false</param-value>

                         <Bundle-Description>API Management Application Bundle</Bundle-Description>
                         <Private-Package>io.entgra.device.mgt.core.apimgt.application.extension.internal</Private-Package>
                         <Import-Packages>
+                            com.google.gson.*;version="${google.gson.version}",

+        return username;
+    }
+
+    public void setUsername(String username) {

-    private static final OkHttpClient client = new OkHttpClient(HttpsTrustManagerUtils.getSSLClient().newBuilder());
     private static final MediaType JSON = MediaType.parse("application/json; charset=utf-8");
     private static final Gson gson = new Gson();
     private static final String host = System.getProperty(Constants.IOT_CORE_HOST);

+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class OAuthClient implements IOAuthClientService {