add custom auth provider guide
add custom auth provider guide

Catografix/docs,khorne3/docs,Catografix/docs,khorne3/docs,auth0/docs,yvonnewilson/docs,Catografix/docs,jeffreylees/docs,hamzawi06/docs,auth0/docs,Annyv2/docs,yvonnewilson/docs,sandrinodimattia/docs,sandrinodimattia/docs,hamzawi06/docs,yvonnewilson/docs,khorne3/docs,Annyv2/docs,jeffreylees/docs,hamzawi06/docs,miparnisari/docs,jeffreylees/docs,auth0/docs,Annyv2/docs,sandrinodimattia/docs