If you need to integrate Deskpro login with an existing web service account system, consider using the JSON Web Token (JWT) standard.
JWT enables Deskpro to hand off user/agent login requests to a login URL that you provide. Once the user/agent is authenticated (e.g. logs into their account on your service), your service provides a JWT token which tells Deskpro that they are allowed access.
There is a JWT library for most popular web development languages.