Convert the Kerberos 5 credential to Kerberos 4 credential. This is done by sending them to the 524 service in the KDC.
krb524_convert_creds_kdc() converts the Kerberos 5 credential in
in_cred to Kerberos 4 credential that is stored in
credentials.
krb524_convert_creds_kdc_ccache() is diffrent from
krb524_convert_creds_kdc() in that way that if
in_cred doesn't contain a DES session key, then a new one is fetched from the KDC and stored in the cred cache
ccache, and then the KDC is queried to convert the credential.
This interfaces are used to make the migration to Kerberos 5 from Kerberos 4 easier. There are few services that still need Kerberos 4, and this is mainly for compatibility for those services. Some services, like AFS, really have Kerberos 5 supports, but still uses the 524 interface to make the migration easier.