Add pkg/authn/github.Keychain to authenticate with ghcr.io

.github/workflows/ghcr-auth.yaml

@@ -0,0 +1,31 @@
+name: GHCR Authentication test
+
+on:
+  pull_request_target:
+    branches: ['main']
+  push:
+    branches: ['main']
+
+permissions:
+  contents: read
+  packages: read
+
+jobs:
+  krane:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-go@v2
+        with:
+          go-version: 1.17.x
+
+      - name: Install krane
+        working-directory: ./cmd/krane
+        run: go install .
+
+      - name: Test krane + GHCR
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        run: |
+          # List the tags
+          krane ls ghcr.io/${{ github.repository }}

cmd/krane/main.go

@@ -24,6 +24,7 @@ import (
 	"github.com/google/go-containerregistry/cmd/crane/cmd"
 	"github.com/google/go-containerregistry/internal/signal"
 	"github.com/google/go-containerregistry/pkg/authn"
+	"github.com/google/go-containerregistry/pkg/authn/github"
 	"github.com/google/go-containerregistry/pkg/crane"
 	"github.com/google/go-containerregistry/pkg/logs"
 	"github.com/google/go-containerregistry/pkg/v1/google"
@@ -51,6 +52,7 @@ func main() {
 	keychain := authn.NewMultiKeychain(
 		authn.DefaultKeychain,
 		google.Keychain,
+		github.Keychain,
 		amazonKeychain,
 		azureKeychain,
 	)

pkg/authn/github/keychain.go

@@ -0,0 +1,59 @@
+// Copyright 2022 Google LLC All Rights Reserved.
+//
+// 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 github provides a keychain for the GitHub Container Registry.
+package github
+
+import (
+	"net/url"
+	"os"
+
+	"github.com/google/go-containerregistry/pkg/authn"
+)
+
+const ghcrHostname = "ghcr.io"
+
+// Keychain exports an instance of the GitHub Keychain.
+//
+// This keychain matches on requests for ghcr.io and provides the value of the
+// environment variable $GITHUB_TOKEN, if it's set.
+var Keychain authn.Keychain = githubKeychain{}
+
+type githubKeychain struct{}
+
+func (githubKeychain) Resolve(r authn.Resource) (authn.Authenticator, error) {
+	serverURL, err := url.Parse("https://" + r.String())
+	if err != nil {
+		return authn.Anonymous, nil
+	}
+	if serverURL.Hostname() == ghcrHostname {
+		username := os.Getenv("GITHUB_ACTOR")
+		if username == "" {
+			username = "unset"
+		}
+		if tok := os.Getenv("GITHUB_TOKEN"); tok != "" {
+			return githubAuthenticator{username, tok}, nil
+		}
+	}
+	return authn.Anonymous, nil
+}
+
+type githubAuthenticator struct{ username, password string }
+
+func (g githubAuthenticator) Authorization() (*authn.AuthConfig, error) {
+	return &authn.AuthConfig{
+		Username: g.username,
+		Password: g.password,
+	}, nil
+}

pkg/authn/github/keychain_test.go

@@ -0,0 +1,112 @@
+// Copyright 2022 Google LLC All Rights Reserved.
+//
+// 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 github
+
+import (
+	"os"
+	"testing"
+
+	"github.com/google/go-containerregistry/pkg/authn"
+)
+
+// TestKeychain checks that the keychain resolves when $GITHUB_TOKEN is set and
+// the request is for GHCR.
+func TestKeychain(t *testing.T) {
+	username, tok := "octocat", "my-token"
+	os.Setenv("GITHUB_ACTOR", username)
+	os.Setenv("GITHUB_TOKEN", tok)
+	got, err := Keychain.Resolve(resource("ghcr.io/my/repo"))
+	if err != nil {
+		t.Fatalf("Resolve: %v", err)
+	}
+	if got == authn.Anonymous {
+		t.Fatalf("Got anonymous, wanted authenticator")
+	}
+
+	auth, err := got.Authorization()
+	if err != nil {
+		t.Fatalf("Authorization: %v", err)
+	}
+	if auth.Username != username {
+		t.Errorf("Got username %q, want %q", auth.Username, username)
+	}
+	if auth.Password != tok {
+		t.Errorf("Got password %q, want %q", auth.Password, tok)
+	}
+}
+
+// TestKeychainUsernameUnset checks that the keychain resolves an "unset"
+// username when $GITHUB_ACTOR is not set.
+func TestKeychainUsernameUnset(t *testing.T) {
+	tok := "my-token"
+	os.Unsetenv("GITHUB_ACTOR")
+	os.Setenv("GITHUB_TOKEN", tok)
+	got, err := Keychain.Resolve(resource("ghcr.io/my/repo"))
+	if err != nil {
+		t.Fatalf("Resolve: %v", err)
+	}
+	if got == authn.Anonymous {
+		t.Fatalf("Got anonymous, wanted authenticator")
+	}
+
+	auth, err := got.Authorization()
+	if err != nil {
+		t.Fatalf("Authorization: %v", err)
+	}
+	if auth.Username != "unset" {
+		t.Errorf("Got username %q, want unset", auth.Username)
+	}
+	if auth.Password != tok {
+		t.Errorf("Got password %q, want %q", auth.Password, tok)
+	}
+}
+
+// TestKeychainUnset checks that the keychain doesn't resolve when the
+// environment variable is unset.
+func TestKeychainUnset(t *testing.T) {
+	os.Unsetenv("GITHUB_TOKEN")
+
+	got, err := Keychain.Resolve(resource("ghcr.io/my/repo"))
+	if err != nil {
+		t.Fatalf("Resolve: %v", err)
+	}
+	if got != authn.Anonymous {
+		t.Errorf("Resolve(ghcr.io) got %v, want Anonymous", got)
+	}
+}
+
+// TestNoMatch checks that the keychain doesn't resolve for non-GHCR registries.
+func TestNoMatch(t *testing.T) {
+	os.Setenv("GITHUB_TOKEN", "my-token")
+	for _, s := range []string{
+		"gcr.io",
+		"example.com",
+		"ghcr.io.example.com",
+		"invalid-domain-name -- %U)(@*)(%*)@(*#%@",
+	} {
+		got, err := Keychain.Resolve(resource(s))
+		if err != nil {
+			t.Fatalf("Resolve: %v", err)
+		}
+		if got != authn.Anonymous {
+			t.Errorf("Resolve(%q) got %v, want Anonymous", s, got)
+		}
+	}
+}
+
+type resource string
+
+func (r resource) String() string      { return string(r) }
+func (r resource) RegistryStr() string { return string(r) }