Add generic OpenID Connect provider (OAuth2)

This adds the oauth2 provider `oidc`. It needs an additional argument, the OIDC discovery endpoint to figure out where the auth and token URLs are.

Configuration is similar to setting up the Google Authentication with these changes:

 * `OAUTH2_PROVIDER = oidc`
 * `OAUTH2_OIDC_DISCOVERY_ENDPOINT = https://auth.exampe.org/discovery`

vendor/github.com/pquerna/cachecontrol/api.go

@@ -0,0 +1,48 @@
+/**
+ *  Copyright 2015 Paul Querna
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ */
+
+package cachecontrol
+
+import (
+	"github.com/pquerna/cachecontrol/cacheobject"
+
+	"net/http"
+	"time"
+)
+
+type Options struct {
+	// Set to True for a prviate cache, which is not shared amoung users (eg, in a browser)
+	// Set to False for a "shared" cache, which is more common in a server context.
+	PrivateCache bool
+}
+
+// Given an HTTP Request, the future Status Code, and an ResponseWriter,
+// determine the possible reasons a response SHOULD NOT be cached.
+func CachableResponseWriter(req *http.Request,
+	statusCode int,
+	resp http.ResponseWriter,
+	opts Options) ([]cacheobject.Reason, time.Time, error) {
+	return cacheobject.UsingRequestResponse(req, statusCode, resp.Header(), opts.PrivateCache)
+}
+
+// Given an HTTP Request and Response, determine the possible reasons a response SHOULD NOT
+// be cached.
+func CachableResponse(req *http.Request,
+	resp *http.Response,
+	opts Options) ([]cacheobject.Reason, time.Time, error) {
+	return cacheobject.UsingRequestResponse(req, resp.StatusCode, resp.Header, opts.PrivateCache)
+}