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/cacheobject/reasons.go

@@ -0,0 +1,95 @@
+/**
+ *  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 cacheobject
+
+// Repersents a potential Reason to not cache an object.
+//
+// Applications may wish to ignore specific reasons, which will make them non-RFC
+// compliant, but this type gives them specific cases they can choose to ignore,
+// making them compliant in as many cases as they can.
+type Reason int
+
+const (
+
+	// The request method was POST and an Expiration header was not supplied.
+	ReasonRequestMethodPOST Reason = iota
+
+	// The request method was PUT and PUTs are not cachable.
+	ReasonRequestMethodPUT
+
+	// The request method was DELETE and DELETEs are not cachable.
+	ReasonRequestMethodDELETE
+
+	// The request method was CONNECT and CONNECTs are not cachable.
+	ReasonRequestMethodCONNECT
+
+	// The request method was OPTIONS and OPTIONS are not cachable.
+	ReasonRequestMethodOPTIONS
+
+	// The request method was TRACE and TRACEs are not cachable.
+	ReasonRequestMethodTRACE
+
+	// The request method was not recognized by cachecontrol, and should not be cached.
+	ReasonRequestMethodUnkown
+
+	// The request included an Cache-Control: no-store header
+	ReasonRequestNoStore
+
+	// The request included an Authorization header without an explicit Public or Expiration time: http://tools.ietf.org/html/rfc7234#section-3.2
+	ReasonRequestAuthorizationHeader
+
+	// The response included an Cache-Control: no-store header
+	ReasonResponseNoStore
+
+	// The response included an Cache-Control: private header and this is not a Private cache
+	ReasonResponsePrivate
+
+	// The response failed to meet at least one of the conditions specified in RFC 7234 section 3: http://tools.ietf.org/html/rfc7234#section-3
+	ReasonResponseUncachableByDefault
+)
+
+func (r Reason) String() string {
+	switch r {
+	case ReasonRequestMethodPOST:
+		return "ReasonRequestMethodPOST"
+	case ReasonRequestMethodPUT:
+		return "ReasonRequestMethodPUT"
+	case ReasonRequestMethodDELETE:
+		return "ReasonRequestMethodDELETE"
+	case ReasonRequestMethodCONNECT:
+		return "ReasonRequestMethodCONNECT"
+	case ReasonRequestMethodOPTIONS:
+		return "ReasonRequestMethodOPTIONS"
+	case ReasonRequestMethodTRACE:
+		return "ReasonRequestMethodTRACE"
+	case ReasonRequestMethodUnkown:
+		return "ReasonRequestMethodUnkown"
+	case ReasonRequestNoStore:
+		return "ReasonRequestNoStore"
+	case ReasonRequestAuthorizationHeader:
+		return "ReasonRequestAuthorizationHeader"
+	case ReasonResponseNoStore:
+		return "ReasonResponseNoStore"
+	case ReasonResponsePrivate:
+		return "ReasonResponsePrivate"
+	case ReasonResponseUncachableByDefault:
+		return "ReasonResponseUncachableByDefault"
+	}
+
+	panic(r)
+}