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managed_identity_authorizer.go
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managed_identity_authorizer.go
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package auth
import (
"context"
"encoding/json"
"fmt"
"io"
"net/http"
"net/url"
"strconv"
"time"
"github.com/hashicorp/go-azure-sdk/sdk/environments"
"golang.org/x/oauth2"
)
// Copyright (c) HashiCorp Inc. All rights reserved.
// Licensed under the MIT License. See NOTICE.txt in the project root for license information.
type ManagedIdentityAuthorizerOptions struct {
// Api describes the Azure API being used
Api environments.Api
// ClientId is the client ID used when authenticating
ClientId string
// CustomManagedIdentityEndpoint is an optional endpoint from which to obtain an access
// token. When blank, the default is used.
CustomManagedIdentityEndpoint string
}
// NewManagedIdentityAuthorizer returns an authorizer using a Managed Identity for authentication.
func NewManagedIdentityAuthorizer(ctx context.Context, options ManagedIdentityAuthorizerOptions) (Authorizer, error) {
resource, err := environments.Resource(options.Api)
if err != nil {
return nil, fmt.Errorf("determining resource for api %q: %+v", options.Api.Name(), err)
}
conf, err := newManagedIdentityConfig(*resource, options.ClientId, options.CustomManagedIdentityEndpoint)
if err != nil {
return nil, err
}
return conf.TokenSource(ctx)
}
const (
msiDefaultApiVersion = "2018-02-01"
msiDefaultEndpoint = "http://169.254.169.254/metadata/identity/oauth2/token"
msiDefaultTimeout = 10 * time.Second
)
var _ Authorizer = &ManagedIdentityAuthorizer{}
// ManagedIdentityAuthorizer is an Authorizer which supports managed service identity.
type ManagedIdentityAuthorizer struct {
conf *managedIdentityConfig
}
// Token returns an access token acquired from the metadata endpoint.
func (a *ManagedIdentityAuthorizer) Token(ctx context.Context, _ *http.Request) (*oauth2.Token, error) {
if a.conf == nil {
return nil, fmt.Errorf("could not request token: conf is nil")
}
query := url.Values{
"api-version": []string{a.conf.MsiApiVersion},
"resource": []string{a.conf.Resource},
}
if a.conf.ClientID != "" {
query["client_id"] = []string{a.conf.ClientID}
}
url := fmt.Sprintf("%s?%s", a.conf.MsiEndpoint, query.Encode())
body, err := azureMetadata(ctx, url)
if err != nil {
return nil, fmt.Errorf("ManagedIdentityAuthorizer: failed to request token from metadata endpoint: %v", err)
}
var tokenRes struct {
AccessToken string `json:"access_token"`
ClientID string `json:"client_id"`
Resource string `json:"resource"`
TokenType string `json:"token_type"`
ExpiresIn interface{} `json:"expires_in"` // relative seconds from now
ExpiresOn interface{} `json:"expires_on"` // timestamp
ExtExpiresIn interface{} `json:"ext_expires_in"` // relative seconds from now
}
if err := json.Unmarshal(body, &tokenRes); err != nil {
return nil, fmt.Errorf("ManagedIdentityAuthorizer: failed to unmarshal token: %v", err)
}
token := &oauth2.Token{
AccessToken: tokenRes.AccessToken,
TokenType: tokenRes.TokenType,
}
var secs time.Duration
if exp, ok := tokenRes.ExpiresIn.(string); ok && exp != "" {
if v, err := strconv.Atoi(exp); err == nil {
secs = time.Duration(v)
}
} else if exp, ok := tokenRes.ExpiresIn.(int64); ok {
secs = time.Duration(exp)
} else if exp, ok := tokenRes.ExpiresIn.(float64); ok {
secs = time.Duration(exp)
}
if secs > 0 {
token.Expiry = time.Now().Add(secs * time.Second)
}
return token, nil
}
// AuxiliaryTokens returns additional tokens for auxiliary tenant IDs, for use in multi-tenant scenarios
func (a *ManagedIdentityAuthorizer) AuxiliaryTokens(_ context.Context, _ *http.Request) ([]*oauth2.Token, error) {
return nil, fmt.Errorf("auxiliary tokens are not supported with MSI authentication")
}
// managedIdentityConfig configures an ManagedIdentityAuthorizer.
type managedIdentityConfig struct {
// ClientID is optionally used to determine which application to assume when a resource has multiple managed identities
ClientID string
// MsiApiVersion is the API version to use when requesting a token from the metadata service
MsiApiVersion string
// MsiEndpoint is the endpoint where the metadata service can be found
MsiEndpoint string
// Resource is the service for which to request an access token
Resource string
}
// newManagedIdentityConfig returns a new managedIdentityConfig with a configured metadata endpoint and resource.
// clientId and objectId can be left blank when a single managed identity is available
func newManagedIdentityConfig(resource, clientId, customManagedIdentityEndpoint string) (*managedIdentityConfig, error) {
endpoint := msiDefaultEndpoint
if customManagedIdentityEndpoint != "" {
endpoint = customManagedIdentityEndpoint
}
return &managedIdentityConfig{
ClientID: clientId,
Resource: resource,
MsiApiVersion: msiDefaultApiVersion,
MsiEndpoint: endpoint,
}, nil
}
// TokenSource provides a source for obtaining access tokens using ManagedIdentityAuthorizer.
func (c *managedIdentityConfig) TokenSource(ctx context.Context) (Authorizer, error) {
return NewCachedAuthorizer(&ManagedIdentityAuthorizer{
conf: c,
})
}
func azureMetadata(ctx context.Context, url string) (body []byte, err error) {
var req *http.Request
req, err = http.NewRequestWithContext(ctx, http.MethodGet, url, http.NoBody)
if err != nil {
return
}
req.Header = http.Header{
"Metadata": []string{"true"},
}
client := &http.Client{
Timeout: msiDefaultTimeout,
}
var resp *http.Response
resp, err = client.Do(req)
if err != nil {
return
}
body, err = io.ReadAll(resp.Body)
if err != nil {
return
}
defer resp.Body.Close()
if c := resp.StatusCode; c < 200 || c > 299 {
err = fmt.Errorf("received HTTP status %d with body: %s", resp.StatusCode, body)
return
}
return
}