When granting acceess to your account to an application never use login/password (which you should not have when using SSO ^^).
To create App specific credentials go to Settings / Security / Create new app password (At the bottom of the page, you need first to fill an app/device name).
When an application need to write files to Nextcloud it can be useful to use share links to limit where it can writes.
To create such link, on a folder click on settings (or right click) then details then + next to Share link. Change permission to edit then copy the link, it look something like this: https://cloud.sparkway.org/index.php/s/XTwECPE4trwF9yM. The last part XTwECPE4trwF9yM can be used as credentials to give folder specific access using webdav.
Settings will look like :
XTwECPE4trwF9yMXTwECPE4trwF9yM