Publications and other rights of distant assistance or supervisor (technical support), has to be secured and granted. But the local supervisor doesn't accept to add external member as co-author or thesis co-supervisor.
this case happened to me for my own Ph.D. thesis. My department didn't allow any external supervisor. So, I asked my supervisor to officially write a letter to my external co-supervisor that his help throughout my Ph.D thesis will be acknowledged and he will be considered as only co-author in any possible publications. the external university accepted the letter and provided all the facilities which I required.
Thank you @Payam, I think we are dealing with issue related to intellectual property protection (IP), the collaboration network might be extended to industry and public partners around the world.
How to protect the rights of each member with simple manner that doesn't add extra weight on students shoulder and independent about the internal supervisor preference?
Some university post-graduate units usually give guidance concerning eligibility and sequence of authorship. Kindly check with your university if such is available. It might help!
Yes, first you should check with your department or university on ethical guidelines with co-authorship as well as rules around an external supervisor. I’m surprised that your university wouldn’t allow an external. Then you should speak to your local supervisor about having this person assist in some way, if it means adding him or her as a co-author, then so be it. But you have to be careful about this arrangement because it could be considered unethical to promise coauthorship in exchange for research supervision.