Support Azure OIDC authentication

- Add packages auth, azure to fetch access token using azidentity DefaultAzureCredential API and default ARM scope

- Provide the capability to override the scope of the access token for Azure DevOps.

- Provide the capability to pass proxy settings to the client options if specified.

- Provide the option to specify a fake token credential for unit tests.

- Add ProviderOptions in git AuthOptions to configure the provider options from consumers.

- Use the credentials API to fetch Azure DevOps access token if the provider is Azure from gogit client.

Signed-off-by: Dipti Pai <[email protected]>

auth/azure/client.go

@@ -0,0 +1,111 @@
+/*
+Copyright 2024 The Flux authors
+
+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 azure
+
+import (
+	"context"
+	"net/http"
+	"net/url"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore/cloud"
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore/policy"
+	"github.com/Azure/azure-sdk-for-go/sdk/azidentity"
+)
+
+const (
+	// 499b84ac-1321-427f-aa17-267ca6975798 is the UUID of Azure Devops
+	// resource. The scope defined below provides access to Azure DevOps
+	// Services REST API. The Microsoft Entra ID access token with this scope
+	// can be used to call Azure DevOps API by passing it in the headers as a
+	// Bearer Token : https://learn.microsoft.com/en-us/azure/devops/integrate/get-started/authentication/service-principal-managed-identity?view=azure-devops#q-can-i-use-a-service-principal-or-managed-identity-with-azure-cli
+	AzureDevOpsRestApiScope = "499b84ac-1321-427f-aa17-267ca6975798/.default"
+)
+
+// Client is an authentication provider for Azure.
+type Client struct {
+	credential azcore.TokenCredential
+	scopes     []string
+	proxyURL   *url.URL
+}
+
+// OptFunc enables specifying options for the provider.
+type OptFunc func(*Client)
+
+// New returns a new authentication provider for Azure. It configures
+// credentials using a default credential chain with options.
+// https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/sdk/azidentity#NewDefaultAzureCredential
+// The default scope is to ARM endpoint in Azure Cloud. The scope is overridden
+// using OptFunc.
+func New(opts ...OptFunc) (*Client, error) {
+	p := &Client{}
+	for _, opt := range opts {
+		opt(p)
+	}
+
+	clientOpts := &azidentity.DefaultAzureCredentialOptions{}
+
+	if p.proxyURL != nil {
+		transport := http.DefaultTransport.(*http.Transport).Clone()
+		transport.Proxy = http.ProxyURL(p.proxyURL)
+		clientOpts.ClientOptions.Transport = &http.Client{Transport: transport}
+	}
+
+	if p.credential == nil {
+		cred, err := azidentity.NewDefaultAzureCredential(clientOpts)
+		if err != nil {
+			return nil, err
+		}
+		p.credential = cred
+	}
+
+	if len(p.scopes) == 0 {
+		p.scopes = []string{cloud.AzurePublic.Services[cloud.ResourceManager].Endpoint + "/" + ".default"}
+	}
+
+	return p, nil
+}
+
+// WithCredential configures the credential to use to fetch the resource manager
+// token.
+func WithCredential(cred azcore.TokenCredential) OptFunc {
+	return func(p *Client) {
+		p.credential = cred
+	}
+}
+
+// WithAzureDevOpsScope() configures the scope to access Azure DevOps Rest API
+// needed to access Azure DevOps Repositories
+func WithAzureDevOpsScope() OptFunc {
+	return func(p *Client) {
+		p.scopes = []string{AzureDevOpsRestApiScope}
+	}
+}
+
+// WithProxyURL sets the proxy URL to use with NewDefaultAzureCredential.
+func WithProxyURL(proxyURL *url.URL) OptFunc {
+	return func(p *Client) {
+		p.proxyURL = proxyURL
+	}
+}
+
+// GetToken gets an OAuth token using azcore TokenCredential
+func (p *Client) GetToken(ctx context.Context) (azcore.AccessToken, error) {
+	return p.credential.GetToken(ctx, policy.TokenRequestOptions{
+		Scopes: p.scopes,
+	})
+}

auth/azure/client_test.go

@@ -0,0 +1,85 @@
+/*
+Copyright 2024 The Flux authors
+
+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 azure
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore/cloud"
+	. "github.com/onsi/gomega"
+)
+
+func TestGetProviderToken(t *testing.T) {
+	tests := []struct {
+		name      string
+		tokenCred azcore.TokenCredential
+		opts      []OptFunc
+		wantToken string
+		wantScope string
+		wantErr   error
+	}{
+		{
+			name: "custom scope",
+			tokenCred: &FakeTokenCredential{
+				Token: "foo",
+			},
+			opts:      []OptFunc{WithAzureDevOpsScope()},
+			wantScope: AzureDevOpsRestApiScope,
+			wantToken: "foo",
+		},
+		{
+			name: "no scope specified",
+			tokenCred: &FakeTokenCredential{
+				Token: "foo",
+			},
+			wantScope: cloud.AzurePublic.Services[cloud.ResourceManager].Endpoint + "/" + ".default",
+			wantToken: "foo",
+		},
+		{
+			name: "error",
+			tokenCred: &FakeTokenCredential{
+				Err: errors.New("oh no!"),
+			},
+			wantErr: errors.New("oh no!"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			g := NewWithT(t)
+			tt.opts = append(tt.opts, WithCredential(tt.tokenCred))
+			client, err := New(tt.opts...)
+			g.Expect(err).ToNot(HaveOccurred())
+			str := ""
+			ctx := context.WithValue(context.TODO(), "scope", &str)
+			token, err := client.GetToken(ctx)
+
+			if tt.wantErr != nil {
+				g.Expect(err).To(HaveOccurred())
+				g.Expect(err).To(Equal(tt.wantErr))
+			} else {
+				g.Expect(err).ToNot(HaveOccurred())
+				g.Expect(token.Token).To(Equal(tt.wantToken))
+				scope := ctx.Value("scope").(*string)
+				g.Expect(*scope).To(Equal(tt.wantScope))
+			}
+		})
+	}
+}

auth/azure/fake_credential.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2024 The Flux authors
+
+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 azure
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore"
+	"github.com/Azure/azure-sdk-for-go/sdk/azcore/policy"
+)
+
+// FakeTokenCredential is a fake Azure credential provider.
+type FakeTokenCredential struct {
+	Token string
+
+	ExpiresOn time.Time
+	Err       error
+}
+
+var _ azcore.TokenCredential = &FakeTokenCredential{}
+
+func (tc *FakeTokenCredential) GetToken(ctx context.Context, options policy.TokenRequestOptions) (azcore.AccessToken, error) {
+	if tc.Err != nil {
+		return azcore.AccessToken{}, tc.Err
+	}
+
+	// Embed the scope inside the context to verify that the desired scope was
+	// specified while fetching the token.
+	val, ok := ctx.Value("scope").(*string)
+	if ok {
+		*val = options.Scopes[0]
+	} else {
+		return azcore.AccessToken{}, fmt.Errorf("unable to get scope")
+	}
+
+	return azcore.AccessToken{Token: tc.Token, ExpiresOn: tc.ExpiresOn}, nil
+}

auth/go.mod

@@ -0,0 +1,27 @@
+module github.com/fluxcd/pkg/auth
+
+go 1.22.4
+
+require (
+	github.com/Azure/azure-sdk-for-go/sdk/azcore v1.12.0
+	github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.7.0
+	github.com/onsi/gomega v1.33.1
+)
+
+require (
+	github.com/Azure/azure-sdk-for-go/sdk/internal v1.9.0 // indirect
+	github.com/AzureAD/microsoft-authentication-library-for-go v1.2.2 // indirect
+	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
+	github.com/golang-jwt/jwt/v5 v5.2.1 // indirect
+	github.com/google/go-cmp v0.6.0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/kylelemons/godebug v1.1.0 // indirect
+	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	golang.org/x/crypto v0.26.0 // indirect
+	golang.org/x/net v0.28.0 // indirect
+	golang.org/x/sys v0.25.0 // indirect
+	golang.org/x/text v0.17.0 // indirect
+	golang.org/x/tools v0.24.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

auth/go.sum

@@ -0,0 +1,56 @@
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+github.com/Azure/azure-sdk-for-go/sdk/azcore v1.12.0/go.mod h1:99EvauvlcJ1U06amZiksfYz/3aFGyIhWGHVyiZXtBAI=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.7.0 h1:tfLQ34V6F7tVSwoTf/4lH5sE0o6eCJuNDTmH09nDpbc=
+github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.7.0/go.mod h1:9kIvujWAA58nmPmWB1m23fyWic1kYZMxD9CxaWn4Qpg=
+github.com/Azure/azure-sdk-for-go/sdk/internal v1.9.0 h1:H+U3Gk9zY56G3u872L82bk4thcsy2Gghb9ExT4Zvm1o=
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+github.com/AzureAD/microsoft-authentication-library-for-go v1.2.2 h1:XHOnouVk1mxXfQidrMEnLlPk9UMeRtyBTnEFtxkV0kU=
+github.com/AzureAD/microsoft-authentication-library-for-go v1.2.2/go.mod h1:wP83P5OoQ5p6ip3ScPr0BAq0BvuPAvacpEuSzyouqAI=
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