Provider in ansible tower

[Akku]

ansible --version

ansible 2.2.1.0

  config file = /etc/ansible/ansible.cfg

  configured module search path = Default w/o overrides

I am using Tower to manage network devices, i have added the username and password as inventory variables to pass the credentials to provider. 

Could someone help how to pass provider in ansible tower other than inventory variable? I tried giving the username and password in the network credentials, But it tower doesn't accept the value from network credentials.