[auth] Fix Bearer credential helper sending Basic auth (400 on image pull)

go/pkg/credhelper/docker.go

@@ -99,6 +99,23 @@ func seedAuthHeaders(host docker.RegistryHost) error {
 	return nil
 }
 
+// bearerAuthFixTransport intercepts requests where containerd has set
+// Authorization: Basic base64("Bearer:<JWT>") (from a credential helper returning
+// Username="Bearer") and converts them to Authorization: Bearer <JWT>.
+// This allows the token endpoint to issue a proper scope-specific token, which
+// containerd then uses for all subsequent registry requests (manifests and blobs).
+type bearerAuthFixTransport struct {
+	token string
+}
+
+func (t *bearerAuthFixTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	clone := req.Clone(req.Context())
+	if username, _, ok := clone.BasicAuth(); ok && username == "Bearer" {
+		clone.Header.Set("Authorization", "Bearer "+t.token)
+	}
+	return http.DefaultTransport.RoundTrip(clone)
+}
+
 func RegistryHostsFromDockerConfig() docker.RegistryHosts {
 	return func(host string) ([]docker.RegistryHost, error) {
 		// FIXME This should be cached somewhere
@@ -126,14 +143,42 @@ func RegistryHostsFromDockerConfig() docker.RegistryHosts {
 			return []docker.RegistryHost{registryHost}, nil
 		}
 
-		registryHost.Authorizer = docker.NewDockerAuthorizer(docker.WithAuthCreds(func(host string) (string, string, error) {
-			p := helperclient.NewShellProgramFunc(fmt.Sprintf("docker-credential-%s", helperName))
+		p := helperclient.NewShellProgramFunc(fmt.Sprintf("docker-credential-%s", helperName))
+		creds, err := helperclient.Get(p, fmt.Sprintf("%s://%s", registryHost.Scheme, registryHost.Host))
+		if err != nil {
+			return nil, err
+		}
 
-			creds, err := helperclient.Get(p, fmt.Sprintf("%s://%s", registryHost.Scheme, registryHost.Host))
+		if creds.Username == "Bearer" {
+			// The credential helper returned a pre-issued Bearer token (Username=="Bearer",
+			// Secret==<JWT>). containerd's WithAuthCreds flow would construct
+			// Authorization: Basic base64("Bearer:<JWT>") for the token endpoint, which
+			// the registry rejects with 400 Bad Request.
+			//
+			// Fix: use a custom transport that converts Basic("Bearer", <JWT>) →
+			// Bearer <JWT> on the wire. This lets the token endpoint issue a proper
+			// scope-specific token, which containerd then uses for all registry requests
+			// (manifests and blobs).
+			customClient := &http.Client{
+				Transport: &bearerAuthFixTransport{token: creds.Secret},
+			}
+			registryHost.Client = customClient
+			registryHost.Authorizer = docker.NewDockerAuthorizer(
+				docker.WithAuthCreds(func(host string) (string, string, error) {
+					return creds.Username, creds.Secret, nil
+				}),
+				docker.WithAuthClient(customClient),
+			)
+
+			err = seedAuthHeaders(registryHost)
 			if err != nil {
-				return "", "", err
+				return nil, err
 			}
 
+			return []docker.RegistryHost{registryHost}, nil
+		}
+
+		registryHost.Authorizer = docker.NewDockerAuthorizer(docker.WithAuthCreds(func(host string) (string, string, error) {
 			return creds.Username, creds.Secret, nil
 		}))