Here, we will enroll the user and create the ecert. enrollment.attrs defines which attributes will be copied into the ecert from user registration. The suffix opt defines which attributes of those copied from registration are optional. If one or more non-optional attributes are not defined on the user registration, the enrollment will fail. The following command will enroll a user with the attribute importer:

fabric-ca-client enroll -u http://user1:pwd1@localhost:7054 --enrollment.attrs "importer,email:opt"