Abstract: Techniques for registering certificates after the issuance of the certificates are provided. A service provider securely registers a client's identity and its certificate without depending on or using an existing basis of trust, such as that provided by domain-joined clients or a security directory (e.g., MICROSOFT's ACTIVE DIRECTORY). The service provider provides services, such as, by way of example and not a limitation, email services, web application services, application services, etc., based on identifiers (e.g., service IDs) issued to registered clients. The service provider subsequently uses the issued identifier to authenticate a client requesting a service or services, and to authorize the client to receive the requested service or services.