This will change the user and password that space has stored for device management and communication.

Use this in case you want to change the credentials that Space has stored for device communication/ management.

To modify the authentication mode on the devices:

1. On the Junos Space Network Management Platform user interface, select Network Management Platform > Devices > Device Management.
2. The Device Management page appears.
3. Select the devices for which you want to modify the authentication.
4. Select Device Access > Modify Authentication from the Actions menu.
5. The Modify Authentication pop-up window is displayed.
6. To modify the existing credentials on the selected devices:
7. In the Username field, enter the username of the device.
   1. If the user does not exist on the device, the user is automatically created.
      1. In the Confirm Password field, reenter the password.
   2. In the Password field, enter the password of the device.

https://www.juniper.net/documentation/us/en/software/junos-space22.3/junos-space-workspaces/topics/task/password-to-key-authentication-changing.html