There's a couple of ways you can do this:
Quick and dirty is to set the option rememberMe:true and add some code that will add the credentials and server to local storage.
The API object only supports browser local storage, so old browsers may not work with the rememberMe:true option. If needed, you can also override the "credentialsStore" object to point somewhere other than localStorage (ie. cookies) by implementing the object (get, set, and clear, as defined in the "defaultCredentialsStore" in the api.js file), and passing it into the GeotabApi() constructor as the 3rd argument. (see screen shot)