MongoDB Enterprise Debian/Ubuntu packages should depend on libsasl2-modules and libsasl2-modules-gssapi-mit. Currently they depend only on libsasl2-2 package only.
This means that PLAIN (ldap) and GSSAPI (kerberos) authentication won't work on a MongoDB Enterprise installation out of the box after installing it using the apt repository.
Please note that the RPM packages in our Redhat/Centos repositories are dependent on the cyrus-sasl, cyrus-sasl-plain, cyrus-sasl-gssapi so the issue is likely only for DEB packages.
If the sasl modules are missing the mongo shell may throw at connection time:
Error: SASL(-4): no mechanism available: No worthy mechs found :
On the other side also the mongod server uses the library for the same authentication purposes.