The format should be "loginname,mailaddres,groupid1;groupid2;".
Neither setting the display name, nor setting roles or passwords is supported (yet).
Example:
testuser1,foobar@example.com,5;2;6
testuser5,foobsdfar@example.com,
testuser5,foobadfar@example.com,0;5;2
testuser2,foobaadsfr@example.com,5;2