Filter Sensitive Data From Requests

Add the ability to filter out sensitive data, using one of three
methods: from headers, from a query string, and by using a custom
callback to modify the request.

Closes #67

vcr/filters.py

@@ -0,0 +1,40 @@
+from six.moves.urllib.parse import urlparse, parse_qsl, urlunparse, urlencode
+import copy
+
+
+def _remove_headers(request, headers_to_remove):
+    out = []
+    for k, v in request.headers:
+        if k.lower() not in [h.lower() for h in headers_to_remove]:
+            out.append((k, v))
+    request.headers = frozenset(out)
+    return request
+
+
+def _remove_query_parameters(request, query_parameters_to_remove):
+    if not hasattr(request, 'path' or not query_parameters_to_remote):
+        return request
+    url = urlparse(request.url)
+    q = parse_qsl(url.query)
+    q = [(k, v) for k, v in q if k not in query_parameters_to_remove]
+    if q:
+        request.path = url.path + '?' + urlencode(q)
+    else:
+        request.path = url.path
+    return request
+
+
+def filter_request(
+        request,
+        filter_headers,
+        filter_query_parameters,
+        before_record
+        ):
+    request = copy.copy(request)  # don't mutate request object
+    if hasattr(request, 'headers') and filter_headers:
+        request = _remove_headers(request, filter_headers)
+    if filter_query_parameters:
+        request = _remove_query_parameters(request, filter_query_parameters)
+    if before_record:
+        request = before_record(request)
+    return request