Add LDAP/Active Directory authentication support

[Hemsby]

Summary

Adds native LDAP authentication to the DNS Server web console, enabling users to sign in with their Active Directory or LDAP directory credentials.

Features

• Three connection modes — plain LDAP, StartTLS (port 389 + SSL), and LDAPS (port 636 + SSL). Mode is selected automatically based on port: Use SSL + port 636 = LDAPS, Use SSL + any other port = StartTLS.
• Service account search — a bind DN/password locates the user in the directory before validating their credentials. Supports UPN (user@domain) and full DN formats.
• Configurable user filter — defaults to (sAMAccountName={0}) for Active Directory; any RFC 4515 filter is supported.
• Group mapping — maps LDAP groups (by CN) to local Technitium groups, e.g. Domain Admins → Administrators.
• Auto-provisioning — optionally creates a local account on first LDAP login, with optional restriction to mapped groups only.
• Ignore SSL errors — for self-signed or internal CA certificates.
• Test connection button — verifies the service account bind without saving config.
• Docker/environment variable support — full headless configuration via DNS_SERVER_LDAP_* variables.

Environment Variables

Variable	Description
DNS_SERVER_LDAP_ENABLED	true/false
DNS_SERVER_LDAP_SERVER	Hostname or IP
DNS_SERVER_LDAP_PORT	Default: 389
DNS_SERVER_LDAP_USE_SSL	true enables StartTLS (port 389) or LDAPS (port 636)
DNS_SERVER_LDAP_IGNORE_SSL_ERRORS	true/false
DNS_SERVER_LDAP_BIND_DN	Service account DN or UPN
DNS_SERVER_LDAP_BIND_PASSWORD	Service account password
DNS_SERVER_LDAP_SEARCH_BASE	e.g. DC=example,DC=com
DNS_SERVER_LDAP_USER_FILTER	Default: (sAMAccountName={0})
DNS_SERVER_LDAP_GROUP_ATTRIBUTE	Default: memberOf
DNS_SERVER_LDAP_ALLOW_SIGNUP	true/false
DNS_SERVER_LDAP_ALLOW_SIGNUP_ONLY_FOR_MAPPED_USERS	true/false
DNS_SERVER_LDAP_GROUP_MAP	JSON array, e.g. [{"remoteGroup":"Domain Admins","localGroup":"Administrators"}]

Implementation Notes

Uses Novell.Directory.Ldap.NETStandard (v3.6.0) rather than System.DirectoryServices.Protocols. The Novell library is pure managed .NET (TcpClient + SslStream) with no dependency on native OpenLDAP libraries, ensuring consistent behaviour on Linux, Windows, macOS, Docker, and ARM.