feat: Add reverse group lookup for LDAP servers that do not return memberOf

[JWuCines]

Description

When using LDAP servers that do not return the memberOf attribute in user search results, group-based authorization denies all requests because Druid cannot determine the user's group memberships. This is a known issue with LDAP servers such as OpenLDAP, where memberOf is either not enabled by default (it requires the memberof overlay module) or is stored as an operational attribute that Java JNDI cannot retrieve — even when ldapsearch returns it correctly.

This PR adds an optional reverse group lookup mechanism to LDAPCredentialsValidator. When configured, if the user search does not return a memberOf attribute, Druid searches group entries to find which groups contain the user's DN and injects the resolved group DNs as synthetic memberOf values into the SearchResult. The existing LDAPRoleProvider (authorizer) then processes these groups as usual, requiring no changes.

The feature is disabled by default. It activates only when both groupBaseDn and groupSearch are configured and the user search result lacks memberOf.

Added reverse group lookup to LDAPCredentialsValidator

Added populateMemberOfFromGroupSearch() method that performs a reverse LDAP search (e.g., (uniqueMember=<userDN>)) against the configured group base DN. The method:

• Uses setReturningAttributes(new String[]{"1.1"}) to request only the DN, minimizing response size.
• Escapes the user DN with encodeForLDAP(userDn, true) to prevent LDAP filter injection.
• Catches NamingException internally and logs an error, so a misconfigured group search does not block user authentication — the user proceeds without group memberships.

Added group search configuration to BasicAuthLDAPConfig

Added two optional fields (groupBaseDn, groupSearch) with a backward-compatible constructor that delegates to the new constructor with null defaults. Added isGroupSearchConfigured() convenience method.

Added helper methods for readability

• hasMemberOfAttribute(SearchResult): checks if memberOf is present on the search result.
• isGroupSearchConfigured(): checks if both group search properties are set.

Added embedded integration test for reverse group lookup

• LdapReverseGroupLookupAuthResource: Extends LdapAuthResource to add groupBaseDn and groupSearch properties to the LDAP credentials validator configuration.
• BasicAuthLdapReverseGroupLookupTest: Extends BasicAuthLdapConfigurationTest to run the full LDAP auth test suite with reverse group lookup enabled. Verifies that group-based authorization works on OpenLDAP (which does not return memberOf by default).

Updated documentation

• docs/development/extensions-core/druid-basic-security.md: Added property reference entries for groupBaseDn and groupSearch.
• docs/operations/auth-ldap.md: Added "Group search reverse lookup configuration" section explaining the problem and configuration. Updated the existing info box to reference both manual role mapping and the new reverse lookup as alternatives.

Updated spellcheck dictionary

• website/.spelling: Added DN and JNDI to the global dictionary to fix 5 spellcheck errors in the new documentation.

Release note

Added support for LDAP group-based authorization on servers that do not return the memberOf attribute (e.g., OpenLDAP). Configure groupBaseDn and groupSearch on the LDAP credentials validator to enable a reverse group lookup that resolves group memberships automatically.

---

Key changed/added classes in this PR

• BasicAuthLDAPConfig
• LDAPCredentialsValidator
• LDAPCredentialsValidatorTest
• LdapReverseGroupLookupAuthResource
• BasicAuthLdapReverseGroupLookupTest

---

This PR has:

• been self-reviewed.
• added documentation for new or modified features or behaviors.
• a release note entry in the PR description.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.

[FrankChen021]

Severity	Findings
P0	0
P1	0
P2	1
P3	0
Total	1

---

This is an automated review by Codex GPT-5

[FrankChen021]

Reviewed 8 of 8 changed files. The reverse group lookup now runs only after password verification, and I found no remaining PR-caused correctness issues in the LDAP reverse lookup changes.

---

This is an automated review by Codex GPT-5

[JWuCines]

Hey @FrankChen021,
Can you have a review and merge to this PR too?
I would like to have it as part of milestone/version 38.0.0
Thank you!

[FrankChen021]

I have reviewed the updated PR for correctness, edge cases, concurrency, and integration risks; no issues found.

Reviewed 8 of 8 changed files.

---

This is an automated review by Codex GPT-5.5

[JWuCines]

@FrankChen021 can you review and approve it? Can you also merge the PR as reviewer and committer?
Thank you!

[JWuCines]

Hi @clintropolis, @gianm and @kfaraz,
I saw your names in PRs and I see you are Member of Apache Druid project.
Can you review and merge this PR, when you have time?
Thank you!

[FrankChen021]

I have reviewed the updated code for correctness, edge cases, concurrency, and integration risks; no issues found. The rebase introduced no PR behavior changes since the previous reviewed SHA.

Reviewed 8 of 8 changed files.

---

This is an automated review by Codex GPT-5.6-Sol