Can't proceed successful login using LDAP via Samba4 AD Domain Controller

Description:

RocketChat doesn't proceed to login with correct credentials on Samba4 DC's own LDAP implementation. Login proceeds with very similar setup on Windows 2008 AD DC but not on Samba4 AD DC.

Steps to reproduce:

1. Configure required fields for LDAP authentication.
2. Test configuration with "TEST CONNECTION" button.
3. See the "Success Connection_success" notification: OK
4. Then try to login with an actual user with correct credentials.

Expected behavior:

1. RocketChat must proceed successful login with correct credentials.
2. Then allow to user login.

Actual behavior:

1. Login failed with "User not found or incorrect password" error.

Server Setup Information:

• Version of Rocket.Chat Server: 0.66.3 - 9c8265045c
• Operating System: Ubuntu 16.0.4
• Deployment Method: snap
• Number of Running Instances: 1
• DB Replicaset Oplog: Enabled
• NodeJS Version: 8.11.3 - x64
• MongoDB Version: 2.6.10-0ubuntu1

Additional context

Log level raised to "Trace" level.
Correct credentials confirmed by logs:
"LDAPResult\",\"status\":0"

Deliberate failed login with incorrect username:
"Error: User not Found"

Deliberate failed login incorrect password:
"Simple Bind Failed: NT_STATUS_LOGON_FAILURE"

Relevant logs:

rocket-ldap.log

Start by reviewing Rocket.Chat's LDAP authentication flow and the attached rocket-ldap.log, comparing the successful connection test with the later user login. Reproduce the Samba4 AD case and determine why valid credentials do not resolve a user; done means successful login with Samba4 while preserving the reported incorrect-password behavior.