User CN name lookup with specific query

README.md

@@ -135,9 +135,47 @@ c.LDAPAuthenticator.user_attribute = 'sAMAccountName'
 c.LDAPAuthenticator.user_attribute = 'uid'
 ```
 
+#### `LDAPAuthenticator.lookup_dn_search_filter` ####
+
+How to query LDAP for user name lookup, if `lookup_dn` is set to True.
+Default value ``'({login_attr}={login})'` should be good enough for most use cases.
+
+
+#### `LDAPAuthenticator.lookup_dn_search_user`, `LDAPAuthenticator.lookup_dn_search_password` ####
+
+Technical account for user lookup, if `lookup_dn` is set to True.
+If both lookup_dn_search_user and lookup_dn_search_password are None, then anonymous LDAP query will be done.
+
+
+#### `LDAPAuthenticator.lookup_dn_user_dn_attribute` ####
+
+Attribute containing user's name needed for  building DN string, if `lookup_dn` is set to True.
+See `user_search_base` for info on how this attribute is used.
+For most LDAP servers, this is username.  For Active Directory, it is cn.
+
 ## Compatibility ##
 
 This has been tested against an OpenLDAP server, with the client
 running Python 3.4. Verifications of this code working well with
 other LDAP setups welcome, as are bug reports and patches to make
 it work with other LDAP setups!
+
+
+## Active Directory integration ##
+
+Please use following options for AD integration. This is useful especially in two cases:
+* LDAP Search requires valid user account in order to query user database
+* DN does not contain login but some other field, like CN (actual login is present in sAMAccountName, and we need to lookup CN)
+
+```python
+c.LDAPAuthenticator.lookup_dn = True
+c.LDAPAuthenticator.lookup_dn_search_filter = '({login_attr}={login})'
+c.LDAPAuthenticator.lookup_dn_search_user = 'ldap_search_user_technical_account'
+c.LDAPAuthenticator.lookup_dn_search_password = 'secret'
+c.LDAPAuthenticator.user_search_base = 'ou=people,dc=wikimedia,dc=org'
+c.LDAPAuthenticator.user_attribute = 'sAMAccountName'
+c.LDAPAuthenticator.lookup_dn_user_dn_attribute = 'cn'
+```
+
+In setup above, first LDAP will be searched (with account ldap_search_user_technical_account) for users that have sAMAccountName=login
+Then DN will be constructed using found CN value.

ldapauthenticator/ldapauthenticator.py

@@ -1,4 +1,5 @@
 import ldap3
+from ldap3.utils.conv import escape_filter_chars
 import re
 
 from jupyterhub.auth import Authenticator
@@ -126,8 +127,12 @@ def _server_port_default(self):
 
         ```
         c.LDAPAuthenticator.lookup_dn = True
+        c.LDAPAuthenticator.lookup_dn_search_filter = '({login_attr}={login})'
+        c.LDAPAuthenticator.lookup_dn_search_user = 'ldap_search_user_technical_account'
+        c.LDAPAuthenticator.lookup_dn_search_password = 'secret'
         c.LDAPAuthenticator.user_search_base = 'ou=people,dc=wikimedia,dc=org'
-        c.LDAPAuthenticator.user_attribute = 'uid'
+        c.LDAPAuthenticator.user_attribute = 'sAMAccountName'
+        c.LDAPAuthenticator.lookup_dn_user_dn_attribute = 'cn'
         ```
         """
     )
@@ -146,6 +151,89 @@ def _server_port_default(self):
         """
     )
 
+    lookup_dn_search_filter = Unicode(
+        config=True,
+        default_value='({login_attr}={login})',
+        allow_none=True,
+        help="""
+        How to query LDAP for user name lookup, if `lookup_dn` is set to True.
+        """
+    )
+
+    lookup_dn_search_user = Unicode(
+        config=True,
+        default_value=None,
+        allow_none=True,
+        help="""
+        Technical account for user lookup, if `lookup_dn` is set to True.
+
+        If both lookup_dn_search_user and lookup_dn_search_password are None, then anonymous LDAP query will be done.
+        """
+    )
+
+    lookup_dn_search_password = Unicode(
+        config=True,
+        default_value=None,
+        allow_none=True,
+        help="""
+        Technical account for user lookup, if `lookup_dn` is set to True.
+        """
+    )
+
+    lookup_dn_user_dn_attribute = Unicode(
+        config=True,
+        default_value=None,
+        allow_none=True,
+        help="""
+        Attribute containing user's name needed for  building DN string, if `lookup_dn` is set to True.
+
+        See `user_search_base` for info on how this attribute is used.
+
+        For most LDAP servers, this is username.  For Active Directory, it is cn.
+        """
+    )
+
+    def resolve_username(self, username_supplied_by_user):
+        if self.lookup_dn:
+            server = ldap3.Server(
+                self.server_address,
+                port=self.server_port,
+                use_ssl=self.use_ssl
+            )
+
+            search_filter = self.lookup_dn_search_filter.format(
+                login_attr=self.user_attribute,
+                login=username_supplied_by_user
+            )
+            self.log.debug(
+                "Looking up user with search_base={search_base}, search_filter='{search_filter}', attributes={attributes}".format(
+                    search_base=self.user_search_base,
+                    search_filter=search_filter,
+                    attributes=self.user_attribute
+                )
+            )
+
+            conn = ldap3.Connection(server, user=self.lookup_dn_search_user, password=self.lookup_dn_search_password)
+            is_bound = conn.bind()
+            if not is_bound:
+                self.log.warn("Can't connect to LDAP")
+                return None
+
+            conn.search(
+                search_base=self.user_search_base,
+                search_scope=ldap3.SUBTREE,
+                search_filter=search_filter,
+                attributes=[self.lookup_dn_user_dn_attribute]
+            )
+
+            if len(conn.response) == 0 or 'attributes' not in conn.response[0].keys():
+                self.log.warn('username:%s No such user entry found when looking up with attribute %s', username_supplied_by_user,
+                              self.user_attribute)
+                return None
+            return conn.response[0]['attributes'][self.lookup_dn_user_dn_attribute]
+        else:
+            return username_supplied_by_user
+
     @gen.coroutine
     def authenticate(self, handler, data):
         username = data['username']
@@ -161,7 +249,7 @@ def getConnection(userdn, username, password):
                     username=username,
                     userdn=userdn
             ))
-            conn = ldap3.Connection(server, user=userdn, password=password)
+            conn = ldap3.Connection(server, user=escape_filter_chars(userdn), password=password)
             return conn
 
         # Protect against invalid usernames as well as LDAP injection attacks
@@ -173,13 +261,18 @@ def getConnection(userdn, username, password):
         if password is None or password.strip() == '':
             self.log.warn('username:%s Login denied for blank password', username)
             return None
-        
+
         isBound = False
         self.log.debug("TYPE= '%s'",isinstance(self.bind_dn_template, list))
+
+        resolved_username = self.resolve_username(username)
+        if resolved_username is None:
+            return None
+
         # In case, there are multiple binding templates
         if isinstance(self.bind_dn_template, list):
             for dn in self.bind_dn_template:
-                userdn = dn.format(username=username)
+                userdn = dn.format(username=resolved_username)
                 conn = getConnection(userdn, username, password)
                 isBound = conn.bind()
                 self.log.debug('Status of user bind {username} with {userdn} : {isBound}'.format(
@@ -190,29 +283,12 @@ def getConnection(userdn, username, password):
                 if isBound:
                     break
         else:
-            userdn = self.bind_dn_template.format(username=username)
+            userdn = self.bind_dn_template.format(username=resolved_username)
             conn = getConnection(userdn, username, password)
             isBound = conn.bind()
 
         if isBound:
             if self.allowed_groups:
-                if self.lookup_dn:
-                    # In some cases, like AD, we don't bind with the DN, and need to discover it.
-                    conn.search(
-                        search_base=self.user_search_base,
-                        search_scope=ldap3.SUBTREE,
-                        search_filter='({userattr}={username})'.format(
-                            userattr=self.user_attribute,
-                            username=username
-                        ),
-                        attributes=[self.user_attribute]
-                    )
-
-                    if len(conn.response) == 0:
-                        self.log.warn('username:%s No such user entry found when looking up with attribute %s', username, self.user_attribute)
-                        return None
-                    userdn = conn.response[0]['dn']
-
                 self.log.debug('username:%s Using dn %s', username, userdn)
                 for group in self.allowed_groups:
                     groupfilter = (
@@ -221,7 +297,7 @@ def getConnection(userdn, username, password):
                         '(uniqueMember={userdn})'
                         '(memberUid={uid})'
                         ')'
-                    ).format(userdn=userdn, uid=username)
+                    ).format(userdn=escape_filter_chars(userdn), uid=escape_filter_chars(username))
                     groupattributes = ['member', 'uniqueMember', 'memberUid']
                     if conn.search(
                         group,