What is the difference between required and requisite Pam control flags?

Required PAM control flags dictate essential parameters that must be set for authentication to succeed, establishing mandatory behaviors in the PAM stack. In contrast, requisite flags provide conditions that must be met for the module to continue processing; if a requisite module fails, the entire authentication process is aborted immediately. Essentially, required flags allow the process to continue even if they fail, while requisite flags do not. This distinction impacts how authentication failures are handled in PAM configurations.