ChargeDesk is a Braintree partner and connects to your Braintree account using OAuth. This means that you only need to approve ChargeDesk's access to your Braintree account. No passwords or API keys need to be provided.
Once your ChargeDesk account has been setup, we recommend that you connect Braintree webhooks to ChargeDesk. This will increase the speed with which subscription payments are synchronised. You can do this by going to Setup > Gateways > Configure next to Braintree > Connect Webhooks.