fix: Implement KBS RCAR handshake with cookies

Fixes 'cookie not found' error (401) from KBS by:
1. Adding CookieJar support to KBS client
2. Implementing GetChallenge() to perform /auth handshake and capture session cookie
3. Updating Agent to get challenge, decode nonce, and use it for evidence generation
4. Regenerating mocks

agent/service.go

@@ -533,6 +533,26 @@ func (as *agentService) downloadAndDecryptResource(ctx context.Context, source *
 	// 2. Get TEE evidence for KBS attestation
 	as.logger.Info("getting TEE evidence for KBS attestation")
 
+	// Initialize KBS client first to get the challenge (nonce)
+	as.logger.Info("initiating KBS attestation handshake", "kbs_url", as.computation.KBS.URL)
+	kbsClient := kbs.NewClient(kbs.Config{
+		URL:     as.computation.KBS.URL,
+		Timeout: 30 * time.Second,
+	})
+
+	// Start RCAR handshake - get nonce and establish session cookie
+	nonceStr, err := kbsClient.GetChallenge(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("failed to get KBS challenge: %w", err)
+	}
+	as.logger.Info("received KBS challenge nonce")
+
+	// Decode nonce for Attestation Service
+	nonceBytes, err := base64.StdEncoding.DecodeString(nonceStr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode KBS nonce: %w", err)
+	}
+
 	// Auto-detect the platform type
 	platform := attestation.CCPlatform()
 	as.logger.Info("detected platform type", "platform", platform)
@@ -542,6 +562,8 @@ func (as *agentService) downloadAndDecryptResource(ctx context.Context, source *
 
 	// Use computation ID as report data
 	copy(reportData[:], []byte(as.computation.ID))
+	// Use KBS provided nonce
+	copy(nonce[:], nonceBytes)
 
 	var kbsEvidence []byte
 
@@ -574,15 +596,10 @@ func (as *agentService) downloadAndDecryptResource(ctx context.Context, source *
 	as.logger.Info("evidence prepared for KBS", "kbs_evidence_len", len(kbsEvidence))
 
 	// 3. Attest with KBS and get token
-	as.logger.Info("attesting with KBS", "kbs_url", as.computation.KBS.URL)
+	as.logger.Info("attesting with KBS")
-
-	kbsClient := kbs.NewClient(kbs.Config{
-		URL:     as.computation.KBS.URL,
-		Timeout: 30 * time.Second,
-	})
 
 	runtimeData := kbs.RuntimeData{
-		Nonce: base64.StdEncoding.EncodeToString(nonce[:]),
+		Nonce: nonceStr,
 	}
 
 	token, err := kbsClient.Attest(ctx, kbsEvidence, runtimeData)

pkg/kbs/client.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/http/cookiejar"
 	"time"
 
 	"github.com/absmach/supermq/pkg/errors"
@@ -26,6 +27,9 @@ var (
 
 // Client defines the interface for KBS (Key Broker Service) communication.
 type Client interface {
+	// GetChallenge initiates the attestation handshake and returns the nonce.
+	GetChallenge(ctx context.Context) (string, error)
+
 	// Attest performs attestation with KBS and returns a token.
 	Attest(ctx context.Context, evidence []byte, runtimeData RuntimeData) (string, error)
 
@@ -86,14 +90,57 @@ func NewClient(config Config) Client {
 		config.Timeout = 30 * time.Second
 	}
 
+	jar, _ := cookiejar.New(nil)
+
 	return &kbsClient{
 		config: config,
 		client: &http.Client{
 			Timeout: config.Timeout,
+			Jar:     jar,
 		},
 	}
 }
 
+// GetChallenge initiates the RCAR handshake calling /kbs/v0/auth
+func (c *kbsClient) GetChallenge(ctx context.Context) (string, error) {
+	url := fmt.Sprintf("%s/kbs/v0/auth", c.config.URL)
+
+	authReq := AuthRequest{
+		Version: "0.1.0",
+		TEE:     "sample", // Initial handshake can be generic or specific
+	}
+
+	reqBody, err := json.Marshal(authReq)
+	if err != nil {
+		return "", errors.Wrap(ErrAttestationFailed, err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(reqBody))
+	if err != nil {
+		return "", errors.Wrap(ErrAttestationFailed, err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.client.Do(req)
+	if err != nil {
+		return "", errors.Wrap(ErrAttestationFailed, err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return "", errors.Wrap(ErrAttestationFailed,
+			fmt.Errorf("auth HTTP %d: %s", resp.StatusCode, string(body)))
+	}
+
+	var authResp AuthResponse
+	if err := json.NewDecoder(resp.Body).Decode(&authResp); err != nil {
+		return "", errors.Wrap(ErrInvalidResponse, err)
+	}
+
+	return authResp.Nonce, nil
+}
+
 // Attest performs attestation with KBS and returns a token.
 func (c *kbsClient) Attest(ctx context.Context, evidence []byte, runtimeData RuntimeData) (string, error) {
 	// Build attest request
@@ -115,6 +162,7 @@ func (c *kbsClient) Attest(ctx context.Context, evidence []byte, runtimeData Run
 	}
 	req.Header.Set("Content-Type", "application/json")
 
+	// Cookie jar handles the session cookie automatically
 	resp, err := c.client.Do(req)
 	if err != nil {
 		return "", errors.Wrap(ErrAttestationFailed, err)
@@ -123,6 +171,7 @@ func (c *kbsClient) Attest(ctx context.Context, evidence []byte, runtimeData Run
 
 	if resp.StatusCode != http.StatusOK {
 		body, _ := io.ReadAll(resp.Body)
+		// Try to parse error details if JSON
 		return "", errors.Wrap(ErrAttestationFailed,
 			fmt.Errorf("HTTP %d: %s", resp.StatusCode, string(body)))
 	}