fix: Set certificates before reconnecting to LDAP

[sbernauer]

Description

Hi Flask-AppBuilder team,

we set up Superset - using Flask-AppBuilder - to use an LDAP connection as described in your documentation.
The first time a user tries to log into the Superset instance the login will always fail with the following error shown in the logs:

2022-05-10 13:45:43,341:ERROR:flask_appbuilder.security.manager:{'result': -1, 'desc': "Can't contact LDAP server", 'ctrls': [], 'info': 'error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed (self signed certificate in certificate chain)'}

The second login would than pass (if the credentials are correct).
This patches solves the issue, so that the first login attempt passes.

The docs of python-ldap say

libldap does not materialize all TLS settings immediately. You must use OPT_X_TLS_NEWCTX with value 0 to instruct libldap to apply pending TLS settings and create a new internal TLS context:

We have to set all the certificates before we set OPT_X_TLS_NEWCTX to 0 so that the correct certificates are set.

ADDITIONAL INFORMATION

• Has associated issue:
• Is CRUD MVC related.
• Is Auth, RBAC security related.
• Changes the security db schema.
• Introduces new feature
• Removes existing feature

[dpgaspar]

thank you!