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// Copyright 2016 The go-github AUTHORS. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This file provides functions for validating payloads from GitHub Webhooks.
// GitHub docs: https://developer.github.com/webhooks/securing/#validating-payloads-from-github
package github
import (
"crypto/hmac"
"crypto/sha1"
"crypto/sha256"
"crypto/sha512"
"encoding/hex"
"encoding/json"
"errors"
"fmt"
"hash"
"io/ioutil"
"net/http"
"strings"
)
const (
// sha1Prefix is the prefix used by GitHub before the HMAC hexdigest.
sha1Prefix = "sha1"
// sha256Prefix and sha512Prefix are provided for future compatibility.
sha256Prefix = "sha256"
sha512Prefix = "sha512"
// signatureHeader is the GitHub header key used to pass the HMAC hexdigest.
signatureHeader = "X-Hub-Signature"
// eventTypeHeader is the Github header key used to pass the event type.
eventTypeHeader = "X-Github-Event"
)
var (
// eventTypeMapping maps webhooks types to their corresponding go-github struct types.
eventTypeMapping = map[string]string{
"commit_comment": "CommitCommentEvent",
"create": "CreateEvent",
"delete": "DeleteEvent",
"deployment": "DeploymentEvent",
"deployment_status": "DeploymentStatusEvent",
"fork": "ForkEvent",
"gollum": "GollumEvent",
"integration_installation": "IntegrationInstallationEvent",
"integration_installation_repositories": "IntegrationInstallationRepositoriesEvent",
"issue_comment": "IssueCommentEvent",
"issues": "IssuesEvent",
"label": "LabelEvent",
"member": "MemberEvent",
"membership": "MembershipEvent",
"milestone": "MilestoneEvent",
"organization": "OrganizationEvent",
"page_build": "PageBuildEvent",
"ping": "PingEvent",
"public": "PublicEvent",
"pull_request_review": "PullRequestReviewEvent",
"pull_request_review_comment": "PullRequestReviewCommentEvent",
"pull_request": "PullRequestEvent",
"push": "PushEvent",
"repository": "RepositoryEvent",
"release": "ReleaseEvent",
"status": "StatusEvent",
"team_add": "TeamAddEvent",
"watch": "WatchEvent",
}
)
// genMAC generates the HMAC signature for a message provided the secret key
// and hashFunc.
func genMAC(message, key []byte, hashFunc func() hash.Hash) []byte {
mac := hmac.New(hashFunc, key)
mac.Write(message)
return mac.Sum(nil)
}
// checkMAC reports whether messageMAC is a valid HMAC tag for message.
func checkMAC(message, messageMAC, key []byte, hashFunc func() hash.Hash) bool {
expectedMAC := genMAC(message, key, hashFunc)
return hmac.Equal(messageMAC, expectedMAC)
}
// messageMAC returns the hex-decoded HMAC tag from the signature and its
// corresponding hash function.
func messageMAC(signature string) ([]byte, func() hash.Hash, error) {
if signature == "" {
return nil, nil, errors.New("missing signature")
}
sigParts := strings.SplitN(signature, "=", 2)
if len(sigParts) != 2 {
return nil, nil, fmt.Errorf("error parsing signature %q", signature)
}
var hashFunc func() hash.Hash
switch sigParts[0] {
case sha1Prefix:
hashFunc = sha1.New
case sha256Prefix:
hashFunc = sha256.New
case sha512Prefix:
hashFunc = sha512.New
default:
return nil, nil, fmt.Errorf("unknown hash type prefix: %q", sigParts[0])
}
buf, err := hex.DecodeString(sigParts[1])
if err != nil {
return nil, nil, fmt.Errorf("error decoding signature %q: %v", signature, err)
}
return buf, hashFunc, nil
}
// ValidatePayload validates an incoming GitHub Webhook event request
// and returns the (JSON) payload.
// secretKey is the GitHub Webhook secret message.
//
// Example usage:
//
// func (s *GitHubEventMonitor) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// payload, err := github.ValidatePayload(r, s.webhookSecretKey)
// if err != nil { ... }
// // Process payload...
// }
//
func ValidatePayload(r *http.Request, secretKey []byte) (payload []byte, err error) {
payload, err = ioutil.ReadAll(r.Body)
if err != nil {
return nil, err
}
sig := r.Header.Get(signatureHeader)
if err := validateSignature(sig, payload, secretKey); err != nil {
return nil, err
}
return payload, nil
}
// validateSignature validates the signature for the given payload.
// signature is the GitHub hash signature delivered in the X-Hub-Signature header.
// payload is the JSON payload sent by GitHub Webhooks.
// secretKey is the GitHub Webhook secret message.
//
// GitHub docs: https://developer.github.com/webhooks/securing/#validating-payloads-from-github
func validateSignature(signature string, payload, secretKey []byte) error {
messageMAC, hashFunc, err := messageMAC(signature)
if err != nil {
return err
}
if !checkMAC(payload, messageMAC, secretKey, hashFunc) {
return errors.New("payload signature check failed")
}
return nil
}
// WebHookType returns the event type of webhook request r.
func WebHookType(r *http.Request) string {
return r.Header.Get(eventTypeHeader)
}
// ParseWebHook parses the event payload. For recognized event types, a
// value of the corresponding struct type will be returned (as returned
// by Event.Payload()). An error will be returned for unrecognized event
// types.
//
// Example usage:
//
// func (s *GitHubEventMonitor) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// payload, err := github.ValidatePayload(r, s.webhookSecretKey)
// if err != nil { ... }
// event, err := github.ParseWebHook(github.WebHookType(r), payload)
// if err != nil { ... }
// switch event := event.(type) {
// case *github.CommitCommentEvent:
// processCommitCommentEvent(event)
// case *github.CreateEvent:
// processCreateEvent(event)
// ...
// }
// }
//
func ParseWebHook(messageType string, payload []byte) (interface{}, error) {
eventType, ok := eventTypeMapping[messageType]
if !ok {
return nil, fmt.Errorf("unknown X-Github-Event in message: %v", messageType)
}
event := Event{
Type: &eventType,
RawPayload: (*json.RawMessage)(&payload),
}
return event.Payload(), nil
}
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