This is more of an FYI in case nobody else is using LDAP. Out of the box in the production image when I try to authenticate through LDAP I get:
...
File "/opt/odoo/custom/src/odoo/addons/auth_ldap/models/res_company_ldap.py", line 76, in _connect
connection = ldap.initialize(uri)
File "/usr/local/lib/python3.6/site-packages/ldap/functions.py", line 85, in initialize
return LDAPObject(uri,trace_level,trace_file,trace_stack_limit,bytes_mode)
File "/usr/local/lib/python3.6/site-packages/ldap/ldapobject.py", line 99, in init
self._trace_level = trace_level or ldap._trace_level
AttributeError: module 'ldap' has no attribute '_trace_level' - - -

After some googling I find this is a somewhat common problem, and downgrade python-ldap to 3.0.0 and the problem goes away. Not sure what it is about the way Odoo is using python-ldap that causes this.