pkcs11-helper is a library that simplifies the interaction with PKCS#11 providers for end-user applications using a simple API and optional OpenSSL engine. The library allows using multiple PKCS#11 providers at the same time, enumerating available token certificates, or selecting a certificate directly by serialized id, handling card removal and card insert events, handling card re-insert to a different slot, supporting session expiration and much more all using a simple API.