Update: Well, I've found the mongo shell and am testing with that, and I get essentially the same issue there on the problem server, so definitely not a Perl problem, but still wondering what the issue is.

I have this test program which works find on one server:

use MongoDB;
use Data::Dumper;

my $mdb = MongoDB->connect( 'mongodb://xxxxxxx', {
  username => 'xxxxx@xxxxxx.COM',
  auth_mechanism => 'GSSAPI',
});

my $db = $mdb->get_database('testdb');

my $cfg = $db->get_collection('test_coll');

my $result = $cfg->insert_one({
  name => 'test_name',
  test_field => 'this_is_a_test',
});

my $id = $result->inserted_id();
print "Inserted: $id\n";

my $all_cfg = $cfg->find;

while ( my $c = $all_cfg->next ) {
  print Dumper $c;
}
[download]

But on another server gets this error on the insert:

MongoDB::AuthError: Authentication to //xxxxxxx:27017 failed: MongoDB:
+:AuthError: GSSAPI error: MongoDB::AuthError: Could not start GSSAPI.
+ Did you run kinit?  Error was: no mechanism available; SASL(-4): no 
+mechanism available: No worthy mechs found; client_start error. (Call
+backs?)
[download]

And yes, I did run kinit on both systems. Authen::SASL::XS is installed on both systems, I'm not real familiar with sasl, gssapi, kerberos...and not sure where to start. How to start tracking down the problem?