There is a trusted driver model of integrating the Deliveries API, which is in preview. In this model, you use the Fleet Engine Delivery Trusted Driver User role to grant permission to create and update delivery vehicles and tasks, including updating the delivery vehicle location and task status or outcome. Tokens issued by a service account with this role are typically used from your delivery driver's mobile devices or from your backend servers.
For more information on the roles Google Maps Platform Last Mile Fleet Solution uses for trusted models, see Cloud project setup.
You should only do a complete integration from mobile devices if you own and manage the devices. That ensures that they can be completely trusted. You can then create vehicles and tasks directly from the Driver SDK.
Note: For security reasons, tokens should only be minted on your backend servers and then shared with clients.
For assistance understanding the implications of this model and implementing it, please open a support case.