La Credencial del Peregrino

[David planning Le Chemin de St Jacques/El Camino de Santiago]

What is the most appropriate way to obtain la credencial prior to the start
of a pilgrimage?
I see that I could request one from the US Friends (after joining) or from
the UK CSJ (after joining) or presumably at my start in Cluny or later
in Le Puy, by asking around the churches there.    Are there any traditions
or rules governing this?    Does it matter prior to entering Spain -
do any of the lodgings along the routes in France care about or require it?
I'd probably carry one in France anyway,
just to collect the stamps at each stop.