add user_format_string to allow use with AD

[TomGoedeme]

Description

We encountered issues with LDAP login integration using our Active Directory (AD) when binding with the user_attr format. This update introduces a new user_format property in the LDAP configuration. This property accepts a Python format string, which defaults to the previous configuration but allows for custom user string formats.

config example:

  ldap:
    dn: OU=BASE,DC=foo,DC=local
    group_attr: memberOf
    red_group: "CN=Some Security Group Name,OU=Security Groups,OU=BASE,DC=foo,DC=local"
    server: ldaps://dc-prod04.foo.local:636
    user_attr: userPrincipalName
    user_format: "{user}"

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Current testing is broken on Caldera(see #3013). But this is being used in production.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[uruwhy]

Suggested change

	user_string = '%s=%s,%s' % (user_attr, username, dn)
	user_format_string = self._ldap_config.get("user_format") or "{user_attr}={user},{dn}"
	user_string = user_format_string.format(user_attr=user_attr, user=username, dn=dn)
	user_format_string = self._ldap_config.get("user_format") or "{user_attr}={user},{dn}"
	try:
	user_string = user_format_string.format(user_attr=user_attr, user=username, dn=dn)
	except KeyError:
	user_string = '%s=%s,%s' % (user_attr, username, dn)

In case users provide a user_format value in their LDAP config that doesn't contain the required parameters, we should default to the previous format.