Add Kerberos and NTLM authentication support

Fixes #41

config/sample-config.yaml

@@ -5,13 +5,25 @@
 # Connection parameters to LDAP server
 # see also: http://net-ldap.rubyforge.org/Net/LDAP.html#method-c-new
 ldap_connection:
-  host: localhost
+  host: ldapserver
   port: 389
   auth:
     method: :simple
     username: CN=username,OU=!Serviceaccounts,OU=company,DC=company,DC=de
     password: secret
 
+  # or GSSAPI / Kerberos authentication:
+  auth:
+    method: :gssapi
+    hostname: ldapserver
+
+  # or GSS-SPNEGO / NTLM authentication
+  auth:
+    method: :gss_spnego
+    domain: 'company.de'
+    username: 'myuser'
+    password: 'secret'
+
 # Search parameters for LDAP users which should be synchronized
 ldap_users:
   base: OU=company,OU=company,DC=company,DC=de