fix(backend): implement protocol-agnostic header setting for dual gRPC/Connect-RPC support

Problem:
The codebase supports both native gRPC and Connect-RPC protocols, but auth
service was using grpc.SetHeader() which only works for native gRPC. This
caused "failed to set grpc header" errors when using Connect-RPC clients
(browsers using nice-grpc-web).

Solution:
- Created HeaderCarrier pattern for protocol-agnostic header setting
- HeaderCarrier stores headers in context for Connect-RPC requests
- Falls back to grpc.SetHeader for native gRPC requests
- Updated auth service to use SetResponseHeader() instead of grpc.SetHeader()
- Refactored Connect wrappers to use withHeaderCarrier() helper to eliminate
  code duplication

Additional fixes:
- Allow public methods when gRPC metadata is missing in ACL interceptor
- Properly handle ParseSessionCookieValue errors instead of ignoring them
- Fix buildSessionCookie to gracefully handle missing metadata

Files changed:
- server/router/api/v1/header_carrier.go: New protocol-agnostic header carrier
- server/router/api/v1/auth_service.go: Use SetResponseHeader, handle missing metadata
- server/router/api/v1/connect_services.go: Use withHeaderCarrier helper
- server/router/api/v1/acl.go: Allow public methods without metadata
- server/router/api/v1/connect_interceptors.go: Handle ParseSessionCookieValue errors

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server/router/api/v1/acl.go

@@ -53,6 +53,10 @@ func NewGRPCAuthInterceptor(store *store.Store, secret string) *GRPCAuthIntercep
 func (in *GRPCAuthInterceptor) AuthenticationInterceptor(ctx context.Context, request any, serverInfo *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
 	md, ok := metadata.FromIncomingContext(ctx)
 	if !ok {
+		// If metadata is missing, only allow public methods
+		if IsPublicMethod(serverInfo.FullMethod) {
+			return handler(ctx, request)
+		}
 		return nil, status.Errorf(codes.Unauthenticated, "failed to parse metadata from incoming context")
 	}
 
@@ -60,7 +64,12 @@ func (in *GRPCAuthInterceptor) AuthenticationInterceptor(ctx context.Context, re
 	if sessionCookie := extractSessionCookieFromMetadata(md); sessionCookie != "" {
 		user, err := in.authenticator.AuthenticateBySession(ctx, sessionCookie)
 		if err == nil && user != nil {
-			_, sessionID, _ := auth.ParseSessionCookieValue(sessionCookie)
+			_, sessionID, err := auth.ParseSessionCookieValue(sessionCookie)
+			if err != nil {
+				// This should not happen since AuthenticateBySession already validated the cookie
+				// but handle it gracefully anyway
+				sessionID = ""
+			}
 			ctx, err = in.authenticator.AuthorizeAndSetContext(ctx, serverInfo.FullMethod, user, sessionID, "", IsAdminOnlyMethod)
 			if err != nil {
 				return nil, toGRPCError(err, codes.PermissionDenied)

server/router/api/v1/auth_service.go

@@ -10,7 +10,6 @@ import (
 
 	"github.com/pkg/errors"
 	"golang.org/x/crypto/bcrypt"
-	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/metadata"
 	"google.golang.org/grpc/status"
@@ -237,10 +236,8 @@ func (s *APIV1Service) doSignIn(ctx context.Context, user *store.User, expireTim
 	if err != nil {
 		return status.Errorf(codes.Internal, "failed to build session cookie, error: %v", err)
 	}
-	if err := grpc.SetHeader(ctx, metadata.New(map[string]string{
+	if err := SetResponseHeader(ctx, "Set-Cookie", sessionCookie); err != nil {
-		"Set-Cookie": sessionCookie,
+		return status.Errorf(codes.Internal, "failed to set response header, error: %v", err)
-	})); err != nil {
-		return status.Errorf(codes.Internal, "failed to set grpc header, error: %v", err)
 	}
 
 	return nil
@@ -284,11 +281,9 @@ func (s *APIV1Service) clearAuthCookies(ctx context.Context) error {
 		return errors.Wrap(err, "failed to build session cookie")
 	}
 
-	// Set both cookies in the response
+	// Set cookie in the response
-	if err := grpc.SetHeader(ctx, metadata.New(map[string]string{
+	if err := SetResponseHeader(ctx, "Set-Cookie", sessionCookie); err != nil {
-		"Set-Cookie": sessionCookie,
+		return errors.Wrap(err, "failed to set response header")
-	})); err != nil {
-		return errors.Wrap(err, "failed to set grpc header")
 	}
 	return nil
 }
@@ -305,15 +300,18 @@ func (*APIV1Service) buildSessionCookie(ctx context.Context, sessionCookieValue
 		attrs = append(attrs, "Expires="+expireTime.Format(time.RFC1123))
 	}
 
-	md, ok := metadata.FromIncomingContext(ctx)
+	// Try to determine if the request is HTTPS by checking the origin header
-	if !ok {
+	// Default to non-HTTPS (Strict SameSite) if metadata is not available
-		return "", errors.New("failed to get metadata from context")
+	isHTTPS := false
-	}
+	if md, ok := metadata.FromIncomingContext(ctx); ok {
-	var origin string
 		for _, v := range md.Get("origin") {
-		origin = v
+			if strings.HasPrefix(v, "https://") {
+				isHTTPS = true
+				break
 			}
-	isHTTPS := strings.HasPrefix(origin, "https://")
+		}
+	}
+
 	if isHTTPS {
 		attrs = append(attrs, "SameSite=None")
 		attrs = append(attrs, "Secure")

server/router/api/v1/connect_interceptors.go

@@ -150,7 +150,12 @@ func (in *AuthInterceptor) WrapUnary(next connect.UnaryFunc) connect.UnaryFunc {
 		if sessionCookie := auth.ExtractSessionCookieFromHeader(header.Get("Cookie")); sessionCookie != "" {
 			user, err := in.authenticator.AuthenticateBySession(ctx, sessionCookie)
 			if err == nil && user != nil {
-				_, sessionID, _ := auth.ParseSessionCookieValue(sessionCookie)
+				_, sessionID, err := auth.ParseSessionCookieValue(sessionCookie)
+				if err != nil {
+					// This should not happen since AuthenticateBySession already validated the cookie
+					// but handle it gracefully anyway
+					sessionID = ""
+				}
 				ctx, err = in.authenticator.AuthorizeAndSetContext(ctx, procedure, user, sessionID, "", IsAdminOnlyMethod)
 				if err != nil {
 					return nil, convertAuthError(err)

server/router/api/v1/connect_services.go

@@ -40,29 +40,27 @@ func (s *ConnectServiceHandler) UpdateInstanceSetting(ctx context.Context, req *
 }
 
 // AuthService
+//
+// Auth service methods need special handling for response headers (cookies).
+// We use withHeaderCarrier helper to inject a header carrier into the context,
+// which allows the service to set headers in a protocol-agnostic way.
 
 func (s *ConnectServiceHandler) GetCurrentSession(ctx context.Context, req *connect.Request[v1pb.GetCurrentSessionRequest]) (*connect.Response[v1pb.GetCurrentSessionResponse], error) {
-	resp, err := s.APIV1Service.GetCurrentSession(ctx, req.Msg)
+	return withHeaderCarrier(ctx, func(ctx context.Context) (*v1pb.GetCurrentSessionResponse, error) {
-	if err != nil {
+		return s.APIV1Service.GetCurrentSession(ctx, req.Msg)
-		return nil, convertGRPCError(err)
+	})
-	}
-	return connect.NewResponse(resp), nil
 }
 
 func (s *ConnectServiceHandler) CreateSession(ctx context.Context, req *connect.Request[v1pb.CreateSessionRequest]) (*connect.Response[v1pb.CreateSessionResponse], error) {
-	resp, err := s.APIV1Service.CreateSession(ctx, req.Msg)
+	return withHeaderCarrier(ctx, func(ctx context.Context) (*v1pb.CreateSessionResponse, error) {
-	if err != nil {
+		return s.APIV1Service.CreateSession(ctx, req.Msg)
-		return nil, convertGRPCError(err)
+	})
-	}
-	return connect.NewResponse(resp), nil
 }
 
 func (s *ConnectServiceHandler) DeleteSession(ctx context.Context, req *connect.Request[v1pb.DeleteSessionRequest]) (*connect.Response[emptypb.Empty], error) {
-	resp, err := s.APIV1Service.DeleteSession(ctx, req.Msg)
+	return withHeaderCarrier(ctx, func(ctx context.Context) (*emptypb.Empty, error) {
-	if err != nil {
+		return s.APIV1Service.DeleteSession(ctx, req.Msg)
-		return nil, convertGRPCError(err)
+	})
-	}
-	return connect.NewResponse(resp), nil
 }
 
 // UserService

server/router/api/v1/header_carrier.go

@@ -0,0 +1,122 @@
+package v1
+
+import (
+	"context"
+
+	"connectrpc.com/connect"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/protobuf/proto"
+)
+
+// headerCarrierKey is the context key for storing headers to be set in the response.
+type headerCarrierKey struct{}
+
+// HeaderCarrier stores headers that need to be set in the response.
+//
+// Problem: The codebase supports two protocols simultaneously:
+//   - Native gRPC: Uses grpc.SetHeader() to set response headers
+//   - Connect-RPC: Uses connect.Response.Header().Set() to set response headers
+//
+// Solution: HeaderCarrier provides a protocol-agnostic way to set headers.
+//   - Service methods call SetResponseHeader() regardless of protocol
+//   - For gRPC requests: SetResponseHeader uses grpc.SetHeader directly
+//   - For Connect requests: SetResponseHeader stores headers in HeaderCarrier
+//   - Connect wrappers extract headers from HeaderCarrier and apply to response
+//
+// This allows service methods to work with both protocols without knowing which one is being used.
+type HeaderCarrier struct {
+	headers map[string]string
+}
+
+// newHeaderCarrier creates a new header carrier.
+func newHeaderCarrier() *HeaderCarrier {
+	return &HeaderCarrier{
+		headers: make(map[string]string),
+	}
+}
+
+// Set adds a header to the carrier.
+func (h *HeaderCarrier) Set(key, value string) {
+	h.headers[key] = value
+}
+
+// Get retrieves a header from the carrier.
+func (h *HeaderCarrier) Get(key string) string {
+	return h.headers[key]
+}
+
+// All returns all headers.
+func (h *HeaderCarrier) All() map[string]string {
+	return h.headers
+}
+
+// WithHeaderCarrier adds a header carrier to the context.
+func WithHeaderCarrier(ctx context.Context) context.Context {
+	return context.WithValue(ctx, headerCarrierKey{}, newHeaderCarrier())
+}
+
+// GetHeaderCarrier retrieves the header carrier from the context.
+// Returns nil if no carrier is present.
+func GetHeaderCarrier(ctx context.Context) *HeaderCarrier {
+	if carrier, ok := ctx.Value(headerCarrierKey{}).(*HeaderCarrier); ok {
+		return carrier
+	}
+	return nil
+}
+
+// SetResponseHeader sets a header in the response.
+//
+// This function works for both gRPC and Connect protocols:
+//   - For gRPC: Uses grpc.SetHeader to set headers in gRPC metadata
+//   - For Connect: Stores in HeaderCarrier for Connect wrapper to apply later
+//
+// The protocol is automatically detected based on whether a HeaderCarrier
+// exists in the context (injected by Connect wrappers).
+func SetResponseHeader(ctx context.Context, key, value string) error {
+	// Try Connect first (check if we have a header carrier)
+	if carrier := GetHeaderCarrier(ctx); carrier != nil {
+		carrier.Set(key, value)
+		return nil
+	}
+
+	// Fall back to gRPC
+	return grpc.SetHeader(ctx, metadata.New(map[string]string{
+		key: value,
+	}))
+}
+
+// withHeaderCarrier is a helper for Connect service wrappers that need to set response headers.
+//
+// It injects a HeaderCarrier into the context, calls the service method,
+// and applies any headers from the carrier to the Connect response.
+//
+// Usage in Connect wrappers:
+//
+//	func (s *ConnectServiceHandler) CreateSession(ctx context.Context, req *connect.Request[...]) (*connect.Response[...], error) {
+//	    return withHeaderCarrier(ctx, func(ctx context.Context) (*v1pb.CreateSessionResponse, error) {
+//	        return s.APIV1Service.CreateSession(ctx, req.Msg)
+//	    })
+//	}
+func withHeaderCarrier[T proto.Message](ctx context.Context, fn func(context.Context) (T, error)) (*connect.Response[T], error) {
+	// Inject header carrier for Connect protocol
+	ctx = WithHeaderCarrier(ctx)
+
+	// Call the service method
+	resp, err := fn(ctx)
+	if err != nil {
+		return nil, convertGRPCError(err)
+	}
+
+	// Create Connect response
+	connectResp := connect.NewResponse(resp)
+
+	// Apply any headers set via the header carrier
+	if carrier := GetHeaderCarrier(ctx); carrier != nil {
+		for key, value := range carrier.All() {
+			connectResp.Header().Set(key, value)
+		}
+	}
+
+	return connectResp, nil
+}