qgis plugins - Canceling task currently running in background using PyQGis?

I am trying to close QgsProject on loading layer (if password and username from QgSProject - datasource are incorrect) before QgsCredentialDialog is shown.

on signal :

QgsProject.instance().loadingLayer.connect(self.load_log)

• 
  

  If password and user are correct -> pass

  
  


• 
  

  if password and user are not correct: close the project

  
  

I am using :

    project = QgsProject.instance()
    project.clear()

but QgsCredentialDialog still shows up.

after clear project if I use :

iface.actionExit().trigger()

This shows up:

If I click yes, QgsCredentialDialog is shown again

How do I close the project and everything connected with that project (signals,actions,tasks,connections,...)?

NOTE:

QgsTaskManager().cancelAll() # NOT WORKING
tasks = QgsApplication.taskManager().activeTasks()
for task in tasks:
    print (task.canCancel()) # False

    print (task.description()) # Loading “C:/Users/User/Desktop/some_project.qgs”
    print (task.flags()) # 

    task.cancel() # NOT WORKING

Since task.canCancel() is FALSE (I think that is main problem here), is it possible to change task.canCancel() into TRUE?