We implemented Patron SAML and uses a patron variable field to be the matchpoint. This field contains the patron's email address. Our IdP accepts dots, dash and underscores in patrons' email address. Due to Sierra indexing rules where symbols (including dots, dash and underscores) will be dropped, different patrons with the same letters in their email address but have different symbols in different positions won't be able to authenticate through Patron SAML.
e.g. Patron A's email = abc.def@test.com, Patron B's email = abc_dec@test.com . Both will fail authentication as Sierra will use abcdef@test.com and return both patron records.