krb5_principal_intro man page
krb5_principal_introThe principal handing functions.
— A Kerberos principal is a email address looking string that contains two parts separated by . The second part is the kerberos realm the principal belongs to and the first is a list of 0 or more components. For example
lha@SU.SE host/hummel.it.su.se@SU.SE host/admin@H5L.ORG
See the library functions here: Heimdal Kerberos 5 principal functions