Adds Kerberos authentication to winrm if available

If the `kerberos` module is available, winrm will attempt to establish a
Kerberized connection to a Windows server. This allows use of Windows
domain accounts, which are quite often the only kinds of accounts
enabled on enterprise networks.

This also pulls the `transport_schemes` variable up into the
`winrm.Connection` class. This lets tests or future modifications alter
the list of available schemas without reaching into `Connection.__init__`.

lib/ansible/runner/connection_plugins/winrm.py

@@ -37,6 +37,13 @@ try:
 except ImportError:
     raise errors.AnsibleError("winrm is not installed")
 
+HAVE_KERBEROS = False
+try:
+    import kerberos
+    HAVE_KERBEROS = True
+except ImportError:
+    pass
+
 _winrm_cache = {
     # 'user:pwhash@host:port': <protocol instance>
 }
@@ -47,6 +54,11 @@ def vvvvv(msg, host=None):
 class Connection(object):
     '''WinRM connections over HTTP/HTTPS.'''
 
+    transport_schemes = {
+        'http': [('kerberos', 'http'), ('plaintext', 'http'), ('plaintext', 'https')],
+        'https': [('kerberos', 'https'), ('plaintext', 'http'), ('plaintext', 'https')],
+        }
+
     def __init__(self,  runner, host, port, user, password, *args, **kwargs):
         self.runner = runner
         self.host = host
@@ -72,11 +84,10 @@ class Connection(object):
         if cache_key in _winrm_cache:
             vvvv('WINRM REUSE EXISTING CONNECTION: %s' % cache_key, host=self.host)
             return _winrm_cache[cache_key]
-        transport_schemes = [('plaintext', 'https'), ('plaintext', 'http')] # FIXME: ssl/kerberos
-        if port == 5985:
-            transport_schemes = reversed(transport_schemes)
         exc = None
-        for transport, scheme in transport_schemes:
+        for transport, scheme in self.transport_schemes['http' if port == 5985 else 'https']:
+            if transport == 'kerberos' and not HAVE_KERBEROS:
+                continue
             endpoint = urlparse.urlunsplit((scheme, netloc, '/wsman', '', ''))
             vvvv('WINRM CONNECT: transport=%s endpoint=%s' % (transport, endpoint),
                  host=self.host)