code: @Path("ext/{dataSource}")
      public Object getExtensionResource(
              @PathParam("dataSource") String authProviderIdentifier)
              throws GuacamoleException {
  
          // Pull UserContext defined by the given auth provider identifier
          UserContext userContext = session.getUserContext(authProviderIdentifier);
  
          // Pull resource from user context
          Object resource = userContext.getResource();
          if (resource != null)
              return resource;
  
          // UserContext-specific resource could not be found
          throw new GuacamoleResourceNotFoundException("No such resource.");
  
      }
docs: Returns the arbitrary REST resource exposed by the UserContext
  associated with the AuthenticationProvider having the given identifier.
  
  @param authProviderIdentifier
  The unique identifier of the AuthenticationProvider associated with
  the UserContext whose arbitrary REST service is being retrieved.
  
  @return
  The arbitrary REST resource exposed by the UserContext exposed by
  this UserContextresource.
  
  @throws GuacamoleException
  If no such resource could be found, or if an error occurs while
  retrieving that resource.