src

token_provider.go (7164B)

---

 package imds
 
 import (
 	"context"
 	"errors"
 	"fmt"
 	"net/http"
 	"sync"
 	"sync/atomic"
 	"time"
 
 	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/aws/smithy-go"
 	"github.com/aws/smithy-go/logging"
 
 	"github.com/aws/smithy-go/middleware"
 	smithyhttp "github.com/aws/smithy-go/transport/http"
 )
 
 const (
 	// Headers for Token and TTL
 	tokenHeader     = "x-aws-ec2-metadata-token"
 	defaultTokenTTL = 5 * time.Minute
 )
 
 type tokenProvider struct {
 	client   *Client
 	tokenTTL time.Duration
 
 	token    *apiToken
 	tokenMux sync.RWMutex
 
 	disabled uint32 // Atomic updated
 }
 
 func newTokenProvider(client *Client, ttl time.Duration) *tokenProvider {
 	return &tokenProvider{
 		client:   client,
 		tokenTTL: ttl,
 	}
 }
 
 // apiToken provides the API token used by all operation calls for th EC2
 // Instance metadata service.
 type apiToken struct {
 	token   string
 	expires time.Time
 }
 
 var timeNow = time.Now
 
 // Expired returns if the token is expired.
 func (t *apiToken) Expired() bool {
 	// Calling Round(0) on the current time will truncate the monotonic reading only. Ensures credential expiry
 	// time is always based on reported wall-clock time.
 	return timeNow().Round(0).After(t.expires)
 }
 
 func (t *tokenProvider) ID() string { return "APITokenProvider" }
 
 // HandleFinalize is the finalize stack middleware, that if the token provider is
 // enabled, will attempt to add the cached API token to the request. If the API
 // token is not cached, it will be retrieved in a separate API call, getToken.
 //
 // For retry attempts, handler must be added after attempt retryer.
 //
 // If request for getToken fails the token provider may be disabled from future
 // requests, depending on the response status code.
 func (t *tokenProvider) HandleFinalize(
 	ctx context.Context, input middleware.FinalizeInput, next middleware.FinalizeHandler,
 ) (
 	out middleware.FinalizeOutput, metadata middleware.Metadata, err error,
 ) {
 	if t.fallbackEnabled() && !t.enabled() {
 		// short-circuits to insecure data flow if token provider is disabled.
 		return next.HandleFinalize(ctx, input)
 	}
 
 	req, ok := input.Request.(*smithyhttp.Request)
 	if !ok {
 		return out, metadata, fmt.Errorf("unexpected transport request type %T", input.Request)
 	}
 
 	tok, err := t.getToken(ctx)
 	if err != nil {
 		// If the error allows the token to downgrade to insecure flow allow that.
 		var bypassErr *bypassTokenRetrievalError
 		if errors.As(err, &bypassErr) {
 			return next.HandleFinalize(ctx, input)
 		}
 
 		return out, metadata, fmt.Errorf("failed to get API token, %w", err)
 	}
 
 	req.Header.Set(tokenHeader, tok.token)
 
 	return next.HandleFinalize(ctx, input)
 }
 
 // HandleDeserialize is the deserialize stack middleware for determining if the
 // operation the token provider is decorating failed because of a 401
 // unauthorized status code. If the operation failed for that reason the token
 // provider needs to be re-enabled so that it can start adding the API token to
 // operation calls.
 func (t *tokenProvider) HandleDeserialize(
 	ctx context.Context, input middleware.DeserializeInput, next middleware.DeserializeHandler,
 ) (
 	out middleware.DeserializeOutput, metadata middleware.Metadata, err error,
 ) {
 	out, metadata, err = next.HandleDeserialize(ctx, input)
 	if err == nil {
 		return out, metadata, err
 	}
 
 	resp, ok := out.RawResponse.(*smithyhttp.Response)
 	if !ok {
 		return out, metadata, fmt.Errorf("expect HTTP transport, got %T", out.RawResponse)
 	}
 
 	if resp.StatusCode == http.StatusUnauthorized { // unauthorized
 		t.enable()
 		err = &retryableError{Err: err, isRetryable: true}
 	}
 
 	return out, metadata, err
 }
 
 func (t *tokenProvider) getToken(ctx context.Context) (tok *apiToken, err error) {
 	if t.fallbackEnabled() && !t.enabled() {
 		return nil, &bypassTokenRetrievalError{
 			Err: fmt.Errorf("cannot get API token, provider disabled"),
 		}
 	}
 
 	t.tokenMux.RLock()
 	tok = t.token
 	t.tokenMux.RUnlock()
 
 	if tok != nil && !tok.Expired() {
 		return tok, nil
 	}
 
 	tok, err = t.updateToken(ctx)
 	if err != nil {
 		return nil, err
 	}
 
 	return tok, nil
 }
 
 func (t *tokenProvider) updateToken(ctx context.Context) (*apiToken, error) {
 	t.tokenMux.Lock()
 	defer t.tokenMux.Unlock()
 
 	// Prevent multiple requests to update retrieving the token.
 	if t.token != nil && !t.token.Expired() {
 		tok := t.token
 		return tok, nil
 	}
 
 	result, err := t.client.getToken(ctx, &getTokenInput{
 		TokenTTL: t.tokenTTL,
 	})
 	if err != nil {
 		var statusErr interface{ HTTPStatusCode() int }
 		if errors.As(err, &statusErr) {
 			switch statusErr.HTTPStatusCode() {
 			// Disable future get token if failed because of 403, 404, or 405
 			case http.StatusForbidden,
 				http.StatusNotFound,
 				http.StatusMethodNotAllowed:
 
 				if t.fallbackEnabled() {
 					logger := middleware.GetLogger(ctx)
 					logger.Logf(logging.Warn, "falling back to IMDSv1: %v", err)
 					t.disable()
 				}
 
 			// 400 errors are terminal, and need to be upstreamed
 			case http.StatusBadRequest:
 				return nil, err
 			}
 		}
 
 		// Disable if request send failed or timed out getting response
 		var re *smithyhttp.RequestSendError
 		var ce *smithy.CanceledError
 		if errors.As(err, &re) || errors.As(err, &ce) {
 			atomic.StoreUint32(&t.disabled, 1)
 		}
 
 		if !t.fallbackEnabled() {
 			// NOTE: getToken() is an implementation detail of some outer operation
 			// (e.g. GetMetadata). It has its own retries that have already been exhausted.
 			// Mark the underlying error as a terminal error.
 			err = &retryableError{Err: err, isRetryable: false}
 			return nil, err
 		}
 
 		// Token couldn't be retrieved, fallback to IMDSv1 insecure flow for this request
 		// and allow the request to proceed. Future requests _may_ re-attempt fetching a
 		// token if not disabled.
 		return nil, &bypassTokenRetrievalError{Err: err}
 	}
 
 	tok := &apiToken{
 		token:   result.Token,
 		expires: timeNow().Add(result.TokenTTL),
 	}
 	t.token = tok
 
 	return tok, nil
 }
 
 // enabled returns if the token provider is current enabled or not.
 func (t *tokenProvider) enabled() bool {
 	return atomic.LoadUint32(&t.disabled) == 0
 }
 
 // fallbackEnabled returns false if EnableFallback is [aws.FalseTernary], true otherwise
 func (t *tokenProvider) fallbackEnabled() bool {
 	switch t.client.options.EnableFallback {
 	case aws.FalseTernary:
 		return false
 	default:
 		return true
 	}
 }
 
 // disable disables the token provider and it will no longer attempt to inject
 // the token, nor request updates.
 func (t *tokenProvider) disable() {
 	atomic.StoreUint32(&t.disabled, 1)
 }
 
 // enable enables the token provide to start refreshing tokens, and adding them
 // to the pending request.
 func (t *tokenProvider) enable() {
 	t.tokenMux.Lock()
 	t.token = nil
 	t.tokenMux.Unlock()
 	atomic.StoreUint32(&t.disabled, 0)
 }
 
 type bypassTokenRetrievalError struct {
 	Err error
 }
 
 func (e *bypassTokenRetrievalError) Error() string {
 	return fmt.Sprintf("bypass token retrieval, %v", e.Err)
 }
 
 func (e *bypassTokenRetrievalError) Unwrap() error { return e.Err }
 
 type retryableError struct {
 	Err         error
 	isRetryable bool
 }
 
 func (e *retryableError) RetryableError() bool { return e.isRetryable }
 
 func (e *retryableError) Error() string { return e.Err.Error() }