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github-events: Add multisecret support to trampoline webhook. (#656)
Adds the ability for the trampoline to accept multiple secrets. This tries to retain the existing behavior of the webhook assuming at least one secret by allowing additional secrets to be specified by a similar `WEBHOOK_SECRET_` prefix. Additional secrets must be defined and loaded out of band of the module. Also adds testing for the trampoline to verify behavior. Part of chainguard-dev/internal-dev#1513
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,152 @@ | ||
| package trampoline | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "context" | ||
| "encoding/json" | ||
| "fmt" | ||
| "io" | ||
| "mime" | ||
| "net/http" | ||
| "time" | ||
|
|
||
| "github.com/chainguard-dev/clog" | ||
| cloudevents "github.com/cloudevents/sdk-go/v2" | ||
| "github.com/google/go-github/v61/github" | ||
| "github.com/jonboulle/clockwork" | ||
| ) | ||
|
|
||
| type Server struct { | ||
| client cloudevents.Client | ||
| secrets [][]byte | ||
| clock clockwork.Clock | ||
| } | ||
|
|
||
| func NewServer(client cloudevents.Client, secrets [][]byte) *Server { | ||
| return &Server{ | ||
| client: client, | ||
| secrets: secrets, | ||
| clock: clockwork.NewRealClock(), | ||
| } | ||
| } | ||
|
|
||
| func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) { | ||
| ctx := r.Context() | ||
| log := clog.FromContext(ctx) | ||
|
|
||
| // https://docs.github.com/en/webhooks/using-webhooks/validating-webhook-deliveries | ||
| payload, err := ValidatePayload(r, s.secrets) | ||
| if err != nil { | ||
| log.Errorf("failed to verify webhook: %v", err) | ||
| w.WriteHeader(http.StatusForbidden) | ||
| fmt.Fprintf(w, "failed to verify webhook: %v", err) | ||
| return | ||
| } | ||
|
|
||
| // https://docs.github.com/en/webhooks/webhook-events-and-payloads#delivery-headers | ||
| t := github.WebHookType(r) | ||
| if t == "" { | ||
| log.Errorf("missing X-GitHub-Event header") | ||
| w.WriteHeader(http.StatusBadRequest) | ||
| return | ||
| } | ||
| t = "dev.chainguard.github." + t | ||
| log = log.With("event-type", t) | ||
|
|
||
| var msg struct { | ||
| Action string `json:"action"` | ||
| Repository struct { | ||
| FullName string `json:"full_name"` | ||
| } `json:"repository"` | ||
| } | ||
| if err := json.Unmarshal(payload, &msg); err != nil { | ||
| log.Warnf("failed to unmarshal payload; action and subject will be unset: %v", err) | ||
| } else { | ||
| log = log.With("action", msg.Action, "repo", msg.Repository.FullName) | ||
| } | ||
|
|
||
| log.Debugf("forwarding event: %s", t) | ||
|
|
||
| event := cloudevents.NewEvent() | ||
| event.SetID(github.DeliveryID(r)) | ||
| event.SetType(t) | ||
| event.SetSource(r.Host) | ||
| event.SetSubject(msg.Repository.FullName) | ||
| event.SetExtension("action", msg.Action) | ||
| // Needs to be an extension to be a filterable attribute. | ||
| // See https://github.com/chainguard-dev/terraform-infra-common/blob/main/pkg/pubsub/cloudevent.go | ||
| if id := r.Header.Get("X-GitHub-Hook-ID"); id != "" { | ||
| // Cloud Event attribute spec only allows [a-z0-9] :( | ||
| event.SetExtension("githubhook", id) | ||
| } | ||
| if err := event.SetData(cloudevents.ApplicationJSON, eventData{ | ||
| When: s.clock.Now(), | ||
| Headers: &eventHeaders{ | ||
| HookID: r.Header.Get("X-GitHub-Hook-ID"), | ||
| DeliveryID: r.Header.Get("X-GitHub-Delivery"), | ||
| UserAgent: r.Header.Get("User-Agent"), | ||
| Event: r.Header.Get("X-GitHub-Event"), | ||
| InstallationTargetType: r.Header.Get("X-GitHub-Installation-Target-Type"), | ||
| InstallationTargetID: r.Header.Get("X-GitHub-Installation-Target-ID"), | ||
| }, | ||
| Body: payload, | ||
| }); err != nil { | ||
| log.Errorf("failed to set data: %v", err) | ||
| w.WriteHeader(http.StatusInternalServerError) | ||
| return | ||
| } | ||
|
|
||
| const retryDelay = 10 * time.Millisecond | ||
| const maxRetry = 3 | ||
| rctx := cloudevents.ContextWithRetriesExponentialBackoff(context.WithoutCancel(ctx), retryDelay, maxRetry) | ||
| if ceresult := s.client.Send(rctx, event); cloudevents.IsUndelivered(ceresult) || cloudevents.IsNACK(ceresult) { | ||
| log.Errorf("Failed to deliver event: %v", ceresult) | ||
| w.WriteHeader(http.StatusInternalServerError) | ||
| } | ||
| log.Debugf("event forwarded") | ||
| } | ||
|
|
||
| type eventData struct { | ||
| When time.Time `json:"when"` | ||
| // See https://docs.github.com/en/webhooks/webhook-events-and-payloads#delivery-headers | ||
| Headers *eventHeaders `json:"headers,omitempty"` | ||
| Body json.RawMessage `json:"body"` | ||
| } | ||
|
|
||
| // Relevant headers for GitHub webhook events that we want to record. | ||
| // See https://docs.github.com/en/webhooks/webhook-events-and-payloads#delivery-headers | ||
| type eventHeaders struct { | ||
| HookID string `json:"hook_id,omitempty"` | ||
| DeliveryID string `json:"delivery_id,omitempty"` | ||
| UserAgent string `json:"user_agent,omitempty"` | ||
| Event string `json:"event,omitempty"` | ||
| InstallationTargetType string `json:"installation_target_type,omitempty"` | ||
| InstallationTargetID string `json:"installation_target_id,omitempty"` | ||
| } | ||
|
|
||
| // ValidatePayload validates the payload of a webhook request for a given set of secrets. | ||
| // If any of the secrets are valid, the payload is returned with no error. | ||
| func ValidatePayload(r *http.Request, secrets [][]byte) ([]byte, error) { | ||
| // Largely forked from github.ValidatePayload - we can't use this directly to avoid consuming the body. | ||
| signature := r.Header.Get(github.SHA256SignatureHeader) | ||
| if signature == "" { | ||
| signature = r.Header.Get(github.SHA1SignatureHeader) | ||
| } | ||
| contentType, _, err := mime.ParseMediaType(r.Header.Get("Content-Type")) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
|
||
| body, err := io.ReadAll(r.Body) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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||
| for _, secret := range secrets { | ||
| payload, err := github.ValidatePayloadFromBody(contentType, bytes.NewBuffer(body), signature, secret) | ||
| if err == nil { | ||
| return payload, nil | ||
| } | ||
| } | ||
| return nil, fmt.Errorf("failed to validate payload") | ||
| } |
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