I am not the right person to write this page but here is summary from a pretty good note from Derek Atkins in a thread on the ?OpenAFSInfo mailing list.

In order to setup cross-realm:

1. you need cross-realm Kerberos (a shared key)
2. The foreign cell needs to setup a group to hold users from your.original.cell:
   pts cg system:authuser@your.original.cell -c foreign.cell

The "groupquota" on this group is the number of cross-cell users who can be created. Then, once that is setup, users can create themselves ids in the foreign cell:

1. user needs to obtain a token in the foreign cell:
   aklog -cell foreign.cell
2. user creates themselves an id in the foreign cell:
   pts cu user@your.original.cell -c foreign.cell
3. user gets new tokens with proper ID:
   aklog -cell foreign.cell -force

The use of aklog assumes you have ?KerberosV tickets. Actually, with the ?OpenAFS aklog, you just the last step -- the aklog to the foreign cell does the pts create internally for you.

I've augmented the description with other comments from the thread.

Credits

Ted Anderson - 22 Jan 2002