Thank you for your help!
I will thus find the sacristain.
The Diocesan House don't have credencials, but they kindly give accomodation to pilgrims (best is to contact them in advance) for about 17€ incl breakfast.
Domi By, si vous avez besoin de traductions un jour, n'hésitez pas.
Bon chemin, as you say in French...