Forward all known github headers

Previous implementation was preventing to proxy signature headers,
unless some secret was set up.

By forwarding all the known GitHub headers, upstream service can do this
checks. Note that this do not break the signature validation on this
proxy.

I've also added the sha256 signature header to the list of known GitHub
headers.

Fixes: stakater#94

pkg/providers/github.go

@@ -17,9 +17,10 @@ const (
 
 // Header constants
 const (
-	XHubSignature   = "X-Hub-Signature"
-	XGitHubEvent    = "X-GitHub-Event"
-	XGitHubDelivery = "X-GitHub-Delivery"
+	XHubSignature    = "X-Hub-Signature"
+	XGitHubEvent     = "X-GitHub-Event"
+	XGitHubDelivery  = "X-GitHub-Delivery"
+	XHubSignature256 = "X-Hub-Signature-256"
 )
 
 const (
@@ -39,16 +40,9 @@ func NewGithubProvider(secret string) (*GithubProvider, error) {
 }
 
 func (p *GithubProvider) GetHeaderKeys() []string {
-	if len(strings.TrimSpace(p.secret)) > 0 {
-		return []string{
-			XHubSignature,
-			XGitHubDelivery,
-			XGitHubEvent,
-			ContentTypeHeader,
-		}
-	}
-
 	return []string{
+		XHubSignature,
+		XHubSignature256,
 		XGitHubDelivery,
 		XGitHubEvent,
 		ContentTypeHeader,

pkg/providers/github_test.go

@@ -71,7 +71,7 @@ func TestGithubProvider_GetHeaderKeys(t *testing.T) {
 	}{
 		{
 			name: "TestGetHeaderKeysWithCorrectValues",
-			want: []string{XGitHubDelivery, XGitHubEvent, ContentTypeHeader},
+			want: []string{XHubSignature, XHubSignature256, XGitHubDelivery, XGitHubEvent, ContentTypeHeader},
 		},
 	}
 	for _, tt := range tests {