The details on howto add GSSAPI/Kerberos to your Linux SAP server are nicely explained here (German). The only annoyance is that one has to hand edit the sources for the SNC adaptor. Therefore I've pushed an already patched tree (as desribed in the above document) here:
git clone http://honk.sigxcpu.org/git/sncadapt.git/
To build the source simply do a:
cd sncadapt make
And to "install" the resulting shared object copy to the location you specified for snc/gssapi_lib, e.g.:
cp snckrb5.so /usr/local/lib64/
ktutil -k sapsrv.keytab get SAPService/sapsrv.example.com@EXAMPLE.COM
and copy the resulting file from your KDC to your server.