When using LDAP authentication, log entries do not include usernames for failed login attempts

Description:

When using LDAP authentication, log entries do not include usernames for failed login attempts.

Steps to reproduce:

1. In administration / settings / LDAP, enable LDAP authentication.
2. Configure LDAP host, port, encryption etc. to match your LDAP server.
3. Once your LDAP authentication works, attempt to log in with an intentionally incorrect password.

Expected behavior:

Usernames for failed login attempts get entered into logs normally.

Actual behavior:

Logs appear with "unknown" fields where usernames should appear, albeit with the correct IP address:

Jul 02 08:53:51 rocketchat.ourdomain.net rocketchat[25799]: Failed login detected - Username[unknown] ClientAddress[null] ForwardedFor[undefined] XRealIp[4021:483:12:4028:c::4d] UserAgent[Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:77.0) Gecko/20100101 Firefox/77.0]
Jul 02 08:55:13 rocketchat.ourdomain.net rocketchat[25799]: Failed login detected - Username[unknown] ClientAddress[null] ForwardedFor[undefined] XRealIp[4021:483:12:4028:c::4d] UserAgent[Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:77.0) Gecko/20100101 Firefox/77.0]

Server Setup Information:

• Version of Rocket.Chat Server: 3.4.0
• Operating System: CentOS Linux release 7.8.2003 (Core)
• Deployment Method: tar
• Number of Running Instances: 20
• DB Replicaset Oplog: yes
• NodeJS Version: v12.16.1
• MongoDB Version: v3.6.18

Relevant logs:

Above.