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azkv: Allow specifying auth method and add cachable authentication methods #1777

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8 changes: 8 additions & 0 deletions README.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -336,6 +336,14 @@ which tries several authentication methods, in this order:
3. `Managed Identity credentials <https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/sdk/azidentity#ManagedIdentityCredential>`_
4. `Azure CLI credentials <https://pkg.go.dev/github.com/Azure/azure-sdk-for-go/sdk/azidentity#AzureCLICredential>`_


If you want to force a specific method you can override this with the enviornment variable ``SOPS_AZURE_AUTH_METHOD``
- ``default`` (same as not setting this variable)
- ``msi``
- ``azure-cli``
- ``cached-device-code`` (device code authentication which caches the token in the os keyring)
- ``cached-browser`` (interactive browser authentication which caches the token in the os keyring)

For example, you can use a Service Principal with the following environment variables:

.. code:: bash
Expand Down
149 changes: 148 additions & 1 deletion azkv/keysource.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,14 +9,21 @@ import (
"context"
"encoding/base64"
"fmt"
"path/filepath"
"regexp"
"strings"
"time"

"encoding/json"
"os"
Comment on lines 9 to +18
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These imports aren't properly ordered.


"github.com/Azure/azure-sdk-for-go/sdk/azcore"
"github.com/Azure/azure-sdk-for-go/sdk/azcore/policy"
"github.com/Azure/azure-sdk-for-go/sdk/azcore/to"
"github.com/Azure/azure-sdk-for-go/sdk/azidentity"
azidentitycache "github.com/Azure/azure-sdk-for-go/sdk/azidentity/cache"
"github.com/Azure/azure-sdk-for-go/sdk/security/keyvault/azkeys"
"github.com/pkg/browser"
"github.com/sirupsen/logrus"

"github.com/getsops/sops/v3/logging"
Expand All @@ -25,6 +32,11 @@ import (
const (
// KeyTypeIdentifier is the string used to identify an Azure Key Vault MasterKey.
KeyTypeIdentifier = "azure_kv"

SopsAzureAuthMethodEnv = "SOPS_AZURE_AUTH_METHOD"

cachedBrowserAuthRecordFileName = "azure-auth-record-browser.json"
cachedDeviceCodeAuthRecordFileName = "azure-auth-record-device-code.json"
)

var (
Expand Down Expand Up @@ -230,7 +242,142 @@ func (key *MasterKey) TypeToIdentifier() string {
// azidentity.NewDefaultAzureCredential.
func (key *MasterKey) getTokenCredential() (azcore.TokenCredential, error) {
if key.tokenCredential == nil {
return azidentity.NewDefaultAzureCredential(nil)

authMethod := strings.ToLower(os.Getenv(SopsAzureAuthMethodEnv))
switch authMethod {
case "cached-browser":
return cachedInteractiveBrowserCredentials()
case "cached-device-code":
return cachedDeviceCodeCredentials()
case "azure-cli":
return azidentity.NewAzureCLICredential(nil)
case "msi":
return azidentity.NewManagedIdentityCredential(nil)
// If "DEFAULT" or not explicitly specified then use the default authentication chain.
case "", "default":
return azidentity.NewDefaultAzureCredential(nil)
default:
return nil, fmt.Errorf("Value `%s` is unsupported for environment variable `%s`, to resolve this either leave it unset or use one of `default`/`msi`/`azure-cli`/`cached-browser`/`cached-device-code`", authMethod, SopsAzureAuthMethodEnv)
}
}
return key.tokenCredential, nil
}

func sopsCacheDir() (string, error) {
userCacheDir, err := os.UserCacheDir()
if err != nil {
return "", err
}

cacheDir := filepath.Join(userCacheDir, "/sops")

if err = os.MkdirAll(cacheDir, 0o700); err != nil {
return "", err
}

return cacheDir, nil
}
Comment on lines +266 to +279
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I think it would be better to create a cache package, with something like:

var (
	cacheDir     string
	cacheDirErr  error
	cacheDirOnce sync.Once
)

// Directory returns the path to the SOPS cache directory, creating it if it
// does not exist. The directory with the name "sops" is created in the user's
// cache directory (see [os.UserCacheDir]). Once created, it will not be
// recreated, even if the function is called multiple times. If an error occurs
// while creating the directory, it will be returned on later calls.
func Directory() (string, error) {
	cacheDirOnce.Do(func() {
		base, err := os.UserCacheDir()
		if err != nil {
			cacheDirErr = err
			return
		}

		cacheDir = filepath.Join(base, "sops")
		cacheDirErr = os.MkdirAll(cacheDir, 0o700)
	})
	if cacheDirErr != nil {
		return "", cacheDirErr
	}
	return cacheDir, nil
}

// Put writes the provided data to a file in the SOPS cache directory.
// At present, no validation is performed on the file name, and it is the
// caller's responsibility to ensure that the file name is safe (i.e., does not
// contain path traversal characters or other unsafe elements).
func Put(fileName string, data []byte) error {
	dir, err := Directory()
	if err != nil {
		return err
	}

	filePath := filepath.Join(dir, fileName)
	if err = os.WriteFile(filePath, data, 0o600); err != nil {
		return fmt.Errorf("failed to write to cache file %s: %w", filePath, err)
	}
	return nil
}

// Get reads the contents of a file from the SOPS cache directory.
// If the file does not exist or cannot be read, an error will be returned.
func Get(fileName string) ([]byte, error) {
	dir, err := Directory()
	if err != nil {
		return nil, err
	}

	filePath := filepath.Join(dir, fileName)
	data, err := os.ReadFile(filePath)
	if err != nil {
		return nil, fmt.Errorf("failed to read cache file %s: %w", filePath, err)
	}
	return data, nil
}

// Exists checks if a file exists in the SOPS cache directory.
func Exists(fileName string) (bool, error) {
	dir, err := Directory()
	if err != nil {
		return false, err
	}

	filePath := filepath.Join(dir, fileName)
	if _, err = os.Stat(filePath); err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	}
	return true, nil
}


type CachableTokenCredential interface {
Authenticate(ctx context.Context, opts *policy.TokenRequestOptions) (azidentity.AuthenticationRecord, error)
GetToken(ctx context.Context, opts policy.TokenRequestOptions) (azcore.AccessToken, error)
}

func cacheStoreRecord(cachePath string, record azidentity.AuthenticationRecord) error {
b, err := json.Marshal(record)
if err != nil {
return err
}

return os.WriteFile(cachePath, b, 0600)
}

func cacheLoadRecord(cachePath string) (azidentity.AuthenticationRecord, error) {
var record azidentity.AuthenticationRecord

b, err := os.ReadFile(cachePath)
if err != nil {
return record, err
}

err = json.Unmarshal(b, &record)
if err != nil {
return record, err
}

return record, nil
}

func cacheTokenCredential(cachePath string, tokenCredentialFn func(cache azidentity.Cache, record azidentity.AuthenticationRecord) (CachableTokenCredential, error)) (azcore.TokenCredential, error) {
cache, err := azidentitycache.New(nil)
// Errors if persistent caching is not supported by the current runtime
if err != nil {
return nil, err
}

cachedRecord, cacheLoadErr := cacheLoadRecord(cachePath)

credential, err := tokenCredentialFn(cache, cachedRecord)
if err != nil {
return nil, err
}

// If loading the authenticationRecord from the cachePath failed for any reason (validation, file doesn't exist, not encoded using json, etc.)
if cacheLoadErr != nil {
record, err := credential.Authenticate(context.Background(), nil)
if err != nil {
return nil, err
}

if err = cacheStoreRecord(cachePath, record); err != nil {
return nil, err
}
}

return credential, nil
}

func cachedInteractiveBrowserCredentials() (azcore.TokenCredential, error) {
// The default behaviour of `browser` which `azidentity` is using for the interactive browser authentication method is to write anything the browser prints to stdout to the stdout of the program running it.
// This is not desired since on the initial authentication or when refreshing the cache it would pollute the output of sops.
// To fix this behaviour we redirect the browser stdout -> stderr so any pertinent information written by the browser is not completely hidden from the user but it doesn't mess up the sops output.
browser.Stdout = os.Stderr

cacheDir, err := sopsCacheDir()
if err != nil {
return nil, err
}

return cacheTokenCredential(
filepath.Join(cacheDir, cachedBrowserAuthRecordFileName),
func(cache azidentity.Cache, record azidentity.AuthenticationRecord) (CachableTokenCredential, error) {
return azidentity.NewInteractiveBrowserCredential(&azidentity.InteractiveBrowserCredentialOptions{
AuthenticationRecord: record,
Cache: cache,
})
},
)
}

func cachedDeviceCodeCredentials() (azcore.TokenCredential, error) {
cacheDir, err := sopsCacheDir()
if err != nil {
return nil, err
}

return cacheTokenCredential(
filepath.Join(cacheDir, cachedDeviceCodeAuthRecordFileName),
func(cache azidentity.Cache, record azidentity.AuthenticationRecord) (CachableTokenCredential, error) {
return azidentity.NewDeviceCodeCredential(&azidentity.DeviceCodeCredentialOptions{
AuthenticationRecord: record,
Cache: cache,
// Print the device code authentication information to stderr so we don't pollute the output of sops.
UserPrompt: func(ctx context.Context, dc azidentity.DeviceCodeMessage) error {
_, err := fmt.Fprintln(os.Stderr, dc.Message)
return err

},
})
},
)
}
5 changes: 4 additions & 1 deletion go.mod
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Expand Up @@ -8,6 +8,7 @@ require (
filippo.io/age v1.2.1
github.com/Azure/azure-sdk-for-go/sdk/azcore v1.18.0
github.com/Azure/azure-sdk-for-go/sdk/azidentity v1.8.2
github.com/Azure/azure-sdk-for-go/sdk/azidentity/cache v0.3.2
github.com/Azure/azure-sdk-for-go/sdk/security/keyvault/azkeys v1.3.1
github.com/ProtonMail/go-crypto v1.1.6
github.com/aws/aws-sdk-go-v2 v1.36.3
Expand All @@ -29,6 +30,7 @@ require (
github.com/mitchellh/go-homedir v1.1.0
github.com/mitchellh/go-wordwrap v1.0.1
github.com/ory/dockertest/v3 v3.12.0
github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c
github.com/pkg/errors v0.9.1
github.com/sirupsen/logrus v1.9.3
github.com/stretchr/testify v1.10.0
Expand Down Expand Up @@ -60,6 +62,7 @@ require (
github.com/Azure/azure-sdk-for-go/sdk/internal v1.11.0 // indirect
github.com/Azure/azure-sdk-for-go/sdk/security/keyvault/internal v1.1.1 // indirect
github.com/Azure/go-ansiterm v0.0.0-20250102033503-faa5f7b0171c // indirect
github.com/AzureAD/microsoft-authentication-extensions-for-go/cache v0.1.1 // indirect
github.com/AzureAD/microsoft-authentication-library-for-go v1.4.2 // indirect
github.com/GoogleCloudPlatform/opentelemetry-operations-go/detectors/gcp v1.27.0 // indirect
github.com/GoogleCloudPlatform/opentelemetry-operations-go/exporter/metric v0.51.0 // indirect
Expand Down Expand Up @@ -111,6 +114,7 @@ require (
github.com/hashicorp/go-secure-stdlib/strutil v0.1.2 // indirect
github.com/hashicorp/go-sockaddr v1.0.7 // indirect
github.com/hashicorp/hcl v1.0.0 // indirect
github.com/keybase/go-keychain v0.0.0-20231219164618-57a3676c3af6 // indirect
github.com/kylelemons/godebug v1.1.0 // indirect
github.com/mattn/go-colorable v0.1.14 // indirect
github.com/mattn/go-isatty v0.0.20 // indirect
Expand All @@ -121,7 +125,6 @@ require (
github.com/opencontainers/go-digest v1.0.0 // indirect
github.com/opencontainers/image-spec v1.1.1 // indirect
github.com/opencontainers/runc v1.2.6 // indirect
github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
github.com/pmezard/go-difflib v1.0.0 // indirect
github.com/russross/blackfriday/v2 v2.1.0 // indirect
Expand Down
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