add SecureForm for easier CSRF validation

flask_admin/form/__init__.py

-from wtforms import form
+from wtforms import form, __version__ as wtforms_version
 from wtforms.fields.core import UnboundField
 
 from .fields import *
@@ -32,3 +32,29 @@ def recreate_field(unbound):
         raise ValueError('recreate_field expects UnboundField instance, %s was passed.' % type(unbound))
 
     return unbound.field_class(*unbound.args, **unbound.kwargs)
+
+
+if int(wtforms_version[0]) > 1:
+    # only WTForms 2+ has built-in CSRF functionality
+    from os import urandom
+    from flask import session
+    from wtforms.csrf.session import SessionCSRF
+
+    class SecureForm(BaseForm):
+        """
+            BaseForm with CSRF token generation and validation support.
+
+            Requires WTForms 2+
+        """
+        class Meta:
+            csrf = True
+            csrf_class = SessionCSRF
+            csrf_secret = urandom(24)
+
+            @property
+            def csrf_context(self):
+                return session
+else:
+    class SecureForm(BaseForm):
+        def __init__(self, *args, **kwargs):
+            raise Exception("SecureForm requires WTForms 2+")