Merge pull request #509 from smallstep/herman/attestation-client-request-id

Add `X-Request-Id` and `User-Agent` headers to attestation requests

Author: hslatman

tpm/attestation/client.go

@@ -7,6 +7,7 @@ import (
 	"crypto/x509"
 	"encoding/json"
 	"fmt"
+	"io"
 	"net/http"
 	"net/url"
 	"os"
@@ -214,7 +215,7 @@ func (ac *Client) attest(ctx context.Context, info *tpm.Info, ek *tpm.EK, attest
 	}
 
 	attestURL := ac.baseURL.JoinPath("attest").String()
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, attestURL, bytes.NewReader(body))
+	req, err := newRequest(ctx, http.MethodPost, attestURL, bytes.NewReader(body))
 	if err != nil {
 		return nil, fmt.Errorf("failed creating POST http request for %q: %w", attestURL, err)
 	}
@@ -258,7 +259,7 @@ func (ac *Client) secret(ctx context.Context, secret []byte) (*secretResponse, e
 	}
 
 	secretURL := ac.baseURL.JoinPath("secret").String()
-	req, err := http.NewRequestWithContext(ctx, http.MethodPost, secretURL, bytes.NewReader(body))
+	req, err := newRequest(ctx, http.MethodPost, secretURL, bytes.NewReader(body))
 	if err != nil {
 		return nil, fmt.Errorf("failed creating POST http request for %q: %w", secretURL, err)
 	}
@@ -280,3 +281,14 @@ func (ac *Client) secret(ctx context.Context, secret []byte) (*secretResponse, e
 
 	return &secretResp, nil
 }
+
+func newRequest(ctx context.Context, method, requestURL string, body io.Reader) (*http.Request, error) {
+	req, err := http.NewRequestWithContext(ctx, method, requestURL, body)
+	if err != nil {
+		return nil, err
+	}
+	enforceRequestID(req)
+	setUserAgent(req)
+
+	return req, nil
+}

tpm/attestation/client_simulator_test.go

@@ -78,6 +78,7 @@ func mustParseURL(t *testing.T, urlString string) *url.URL {
 
 func TestClient_Attest(t *testing.T) {
 	ctx := context.Background()
+	ctx = NewRequestIDContext(ctx, "requestID")
 	instance := newSimulatedTPM(t)
 	ak, err := instance.CreateAK(ctx, "ak1")
 	require.NoError(t, err)
@@ -140,6 +141,9 @@ func TestClient_Attest(t *testing.T) {
 			handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 				switch r.URL.Path {
 				case "/attest":
+					assert.Equal(t, "step-attestation-http-client/1.0", r.Header.Get("User-Agent"))
+					assert.Equal(t, "requestID", r.Header.Get("X-Request-Id"))
+
 					var ar attestationRequest
 					err := json.NewDecoder(r.Body).Decode(&ar)
 					require.NoError(t, err)
@@ -165,6 +169,9 @@ func TestClient_Attest(t *testing.T) {
 						Secret:     encryptedCredentials.Secret,
 					})
 				case "/secret":
+					assert.Equal(t, "step-attestation-http-client/1.0", r.Header.Get("User-Agent"))
+					assert.Equal(t, "requestID", r.Header.Get("X-Request-Id"))
+
 					var sr secretRequest
 					err := json.NewDecoder(r.Body).Decode(&sr)
 					require.NoError(t, err)

tpm/attestation/requestid.go

@@ -0,0 +1,52 @@
+package attestation
+
+import (
+	"context"
+	"net/http"
+
+	"go.step.sm/crypto/randutil"
+)
+
+type requestIDContextKey struct{}
+
+// NewRequestIDContext returns a new context with the given request ID added to the
+// context.
+func NewRequestIDContext(ctx context.Context, requestID string) context.Context {
+	return context.WithValue(ctx, requestIDContextKey{}, requestID)
+}
+
+// RequestIDFromContext returns the request ID from the context if it exists.
+// and is not empty.
+func RequestIDFromContext(ctx context.Context) (string, bool) {
+	v, ok := ctx.Value(requestIDContextKey{}).(string)
+	return v, ok && v != ""
+}
+
+// requestIDHeader is the header name used for propagating request IDs from
+// the attestation client to the attestation CA and back again.
+const requestIDHeader = "X-Request-Id"
+
+// newRequestID generates a new random UUIDv4 request ID. If it fails,
+// the request ID will be the empty string.
+func newRequestID() string {
+	requestID, err := randutil.UUIDv4()
+	if err != nil {
+		return ""
+	}
+
+	return requestID
+}
+
+// enforceRequestID checks if the X-Request-Id HTTP header is filled. If it's
+// empty, the context is searched for a request ID. If that's also empty, a new
+// request ID is generated.
+func enforceRequestID(r *http.Request) {
+	if requestID := r.Header.Get(requestIDHeader); requestID == "" {
+		if reqID, ok := RequestIDFromContext(r.Context()); ok {
+			requestID = reqID
+		} else {
+			requestID = newRequestID()
+		}
+		r.Header.Set(requestIDHeader, requestID)
+	}
+}

tpm/attestation/useragent.go

@@ -0,0 +1,12 @@
+package attestation
+
+import "net/http"
+
+// UserAgent is the value of the User-Agent HTTP header that will
+// be set in HTTP requests to the attestation CA.
+var UserAgent = "step-attestation-http-client/1.0"
+
+// setUserAgent sets the User-Agent header in HTTP requests.
+func setUserAgent(r *http.Request) {
+	r.Header.Set("User-Agent", UserAgent)
+}