code: public Observable<List<DatabasePrincipalInner>> listPrincipalsAsync(String resourceGroupName, String clusterName, String databaseName) {
          return listPrincipalsWithServiceResponseAsync(resourceGroupName, clusterName, databaseName).map(new Func1<ServiceResponse<List<DatabasePrincipalInner>>, List<DatabasePrincipalInner>>() {
              @Override
              public List<DatabasePrincipalInner> call(ServiceResponse<List<DatabasePrincipalInner>> response) {
                  return response.body();
              }
          });
      }
docs: Returns a list of database principals of the given Kusto cluster and database.
  
  @param resourceGroupName The name of the resource group containing the Kusto cluster.
  @param clusterName The name of the Kusto cluster.
  @param databaseName The name of the database in the Kusto cluster.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the List&lt;DatabasePrincipalInner&gt; object