External Identity Provider Kit (EIP)
For credential-based documents, the protectedpdf server includes a built-in Identity Provider. The built-in Identity Provider uses email and password pairs as credentials. If you wish to use credentials other than email and password pairs or you wish to maintain your customer information in a system separate from the protectedpdf server (such as a shopping cart), you can implement an EIP. When using an EIP, you may customize credentials to your needs e.g. username and password pairs, serial numbers or even IP address ranges.
EIP Documentation External Identity Provider Kit
EIP Sample Code EIP C#