Unity Cloud Build supports projects hosted in Perforce (see www.perforce.com).
Username and password
In your Perforce server, create a new user for Unity Cloud Build, along with a secure password. If your Perforce host supports it, make this a read-only user account.
Ticket authentication
Using your Perforce administration tools, create a new user. When authenticating against Perforce, Cloud Build retrieves and uses the assigned ticket during the login process.
Unicode-enabled servers
Unity Cloud Build does not support unicode-enabled Perforce servers.
Is something described here not working as you expect it to? It might be a Known Issue. Please check with the Issue Tracker at issuetracker.unity3d.com.