A mapping relationship of a device ID associated with a client, a certificate ID associated with a certificate to be applied by the client during a certificate application process, and identity verification methods to be used to verify the client is stored during the certificate application process. From the client, a request for a certificate to perform a service is received, and the request includes the device ID, an identification verification requirement associated with the service, and the identity verification requirement specifies at least one identity verification method. In response to receiving the request based on the mapping relationship, a certificate ID of an existing certificate that corresponds to the received device ID and satisfies the identity verification requirement is retrieved. In response to retrieving the certificate ID, a certificate response to the client including the retrieved certificate ID is sent.