[RFC-007] Implement GitHub app authentication for git repositories in IAC

- Controller change to use the GitHub authentication information specified in Git Repository's `.spec.secretRef` to create the auth options to authenticate to git repositories when the `provider` field is set to `github`,
- Tests for new `github` provider field in IAC
- Updated docs to use GitHub Apps for authentication in image-automation-controller.

Signed-off-by: Dipti Pai <diptipai89@outlook.com>

docs/spec/v1beta2/imageupdateautomations.md

@@ -257,6 +257,13 @@ patches:
               azure.workload.identity/use: "true"
 ```
 
+##### GitHub
+
+If the provider is set to `github`, make sure the GitHub App is registered and
+installed with the necessary permissions and the github app secret is configured
+as described
+[here](https://fluxcd.io/flux/components/source/gitrepositories/#github).
+
 ### Git specification
 
 `.spec.git` is a required field to specify Git configurations related to source

internal/source/git.go

@@ -32,6 +32,7 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/client"
 
 	"github.com/fluxcd/pkg/auth/azure"
+	"github.com/fluxcd/pkg/auth/github"
 	"github.com/fluxcd/pkg/git"
 	"github.com/fluxcd/pkg/git/gogit"
 	sourcev1 "github.com/fluxcd/source-controller/api/v1"
@@ -181,13 +182,30 @@ func getAuthOpts(ctx context.Context, c client.Client, repo *sourcev1.GitReposit
 		return nil, fmt.Errorf("failed to configure authentication options: %w", err)
 	}
 
-	if repo.GetProvider() == sourcev1.GitProviderAzure {
+	switch repo.GetProvider() {
+	case sourcev1.GitProviderAzure:
 		opts.ProviderOpts = &git.ProviderOptions{
 			Name: sourcev1.GitProviderAzure,
 			AzureOpts: []azure.OptFunc{
 				azure.WithAzureDevOpsScope(),
 			},
 		}
+	case sourcev1.GitProviderGitHub:
+		// if provider is github, but secret ref is not specified
+		if repo.Spec.SecretRef == nil {
+			return nil, fmt.Errorf("secretRef with github app data must be specified when provider is set to github: %w", ErrInvalidSourceConfiguration)
+		}
+		opts.ProviderOpts = &git.ProviderOptions{
+			Name: sourcev1.GitProviderGitHub,
+			GitHubOpts: []github.OptFunc{
+				github.WithAppData(data),
+			},
+		}
+	default:
+		// analyze secret, if it has github app data, perhaps provider should have been github.
+		if appID := data[github.AppIDKey]; len(appID) != 0 {
+			return nil, fmt.Errorf("secretRef '%s/%s' has github app data but provider is not set to github: %w", repo.GetNamespace(), repo.Spec.SecretRef.Name, ErrInvalidSourceConfiguration)
+		}
 	}
 
 	return opts, nil

internal/source/git_test.go

@@ -18,6 +18,7 @@ package source
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"testing"
 	"time"
@@ -34,6 +35,7 @@ import (
 	imagev1 "github.com/fluxcd/image-automation-controller/api/v1beta2"
 	"github.com/fluxcd/image-automation-controller/internal/testutil"
 	"github.com/fluxcd/pkg/apis/meta"
+	"github.com/fluxcd/pkg/auth/github"
 	"github.com/fluxcd/pkg/git"
 	sourcev1 "github.com/fluxcd/source-controller/api/v1"
 )
@@ -141,49 +143,127 @@ func Test_getAuthOpts(t *testing.T) {
 func Test_getAuthOpts_providerAuth(t *testing.T) {
 	tests := []struct {
 		name                 string
+		url                  string
+		secret               *corev1.Secret
 		beforeFunc           func(obj *sourcev1.GitRepository)
 		wantProviderOptsName string
+		wantErr              error
 	}{
 		{
 			name: "azure provider",
+			url:  "https://dev.azure.com/foo/bar/_git/baz",
 			beforeFunc: func(obj *sourcev1.GitRepository) {
 				obj.Spec.Provider = sourcev1.GitProviderAzure
 			},
 			wantProviderOptsName: sourcev1.GitProviderAzure,
 		},
+		{
+			name: "github provider with no secret ref",
+			url:  "https://github.com/org/repo.git",
+			beforeFunc: func(obj *sourcev1.GitRepository) {
+				obj.Spec.Provider = sourcev1.GitProviderGitHub
+			},
+			wantProviderOptsName: sourcev1.GitProviderGitHub,
+			wantErr:              errors.New("secretRef with github app data must be specified when provider is set to github: invalid source configuration"),
+		},
+		{
+			name: "github provider with secret ref that does not exist",
+			url:  "https://github.com/org/repo.git",
+			beforeFunc: func(obj *sourcev1.GitRepository) {
+				obj.Spec.Provider = sourcev1.GitProviderGitHub
+				obj.Spec.SecretRef = &meta.LocalObjectReference{
+					Name: "githubAppSecret",
+				}
+			},
+			wantErr: errors.New("failed to get auth secret '/githubAppSecret': secrets \"githubAppSecret\" not found"),
+		},
+		{
+			name: "github provider with github app data in secret",
+			url:  "https://example.com/org/repo",
+			secret: &corev1.Secret{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: "githubAppSecret",
+				},
+				Data: map[string][]byte{
+					github.AppIDKey:             []byte("123"),
+					github.AppInstallationIDKey: []byte("456"),
+					github.AppPrivateKey:        []byte("abc"),
+				},
+			},
+			beforeFunc: func(obj *sourcev1.GitRepository) {
+				obj.Spec.Provider = sourcev1.GitProviderGitHub
+				obj.Spec.SecretRef = &meta.LocalObjectReference{
+					Name: "githubAppSecret",
+				}
+			},
+			wantProviderOptsName: sourcev1.GitProviderGitHub,
+		},
+		{
+			name: "generic provider with github app data in secret",
+			url:  "https://example.com/org/repo",
+			secret: &corev1.Secret{
+				ObjectMeta: metav1.ObjectMeta{
+					Name: "githubAppSecret",
+				},
+				Data: map[string][]byte{
+					github.AppIDKey: []byte("123"),
+				},
+			},
+			beforeFunc: func(obj *sourcev1.GitRepository) {
+				obj.Spec.Provider = sourcev1.GitProviderGeneric
+				obj.Spec.SecretRef = &meta.LocalObjectReference{
+					Name: "githubAppSecret",
+				}
+			},
+			wantErr: errors.New("secretRef '/githubAppSecret' has github app data but provider is not set to github: invalid source configuration"),
+		},
 		{
 			name: "generic provider",
+			url:  "https://example.com/org/repo",
 			beforeFunc: func(obj *sourcev1.GitRepository) {
 				obj.Spec.Provider = sourcev1.GitProviderGeneric
 			},
 		},
 		{
 			name: "no provider",
+			url:  "https://example.com/org/repo",
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			g := NewWithT(t)
+			clientBuilder := fakeclient.NewClientBuilder().
+				WithScheme(scheme.Scheme).
+				WithStatusSubresource(&sourcev1.GitRepository{})
 
+			if tt.secret != nil {
+				clientBuilder.WithObjects(tt.secret)
+			}
+			c := clientBuilder.Build()
 			obj := &sourcev1.GitRepository{
 				Spec: sourcev1.GitRepositorySpec{
-					URL: "https://dev.azure.com/foo/bar/_git/baz",
+					URL: tt.url,
 				},
 			}
 
 			if tt.beforeFunc != nil {
 				tt.beforeFunc(obj)
 			}
-			opts, err := getAuthOpts(context.TODO(), nil, obj)
+			opts, err := getAuthOpts(context.TODO(), c, obj)
 
-			g.Expect(err).ToNot(HaveOccurred())
+			if tt.wantErr != nil {
-			g.Expect(opts).ToNot(BeNil())
+				g.Expect(err).To(HaveOccurred())
-			if tt.wantProviderOptsName != "" {
+				g.Expect(err.Error()).To(ContainSubstring(tt.wantErr.Error()))
-				g.Expect(opts.ProviderOpts).ToNot(BeNil())
-				g.Expect(opts.ProviderOpts.Name).To(Equal(tt.wantProviderOptsName))
 			} else {
-				g.Expect(opts.ProviderOpts).To(BeNil())
+				g.Expect(err).ToNot(HaveOccurred())
+				g.Expect(opts).ToNot(BeNil())
+				if tt.wantProviderOptsName != "" {
+					g.Expect(opts.ProviderOpts).ToNot(BeNil())
+					g.Expect(opts.ProviderOpts.Name).To(Equal(tt.wantProviderOptsName))
+				} else {
+					g.Expect(opts.ProviderOpts).To(BeNil())
+				}
 			}
 		})
 	}