server: add a WIP middleware example

toolkit/server/context.go

@@ -0,0 +1,28 @@
+package server
+
+import "context"
+
+type contextKey string
+
+var ctxUserId = contextKey("userId")
+var ctxProjectId = contextKey("projectId")
+
+// ContextGetUserId return the UserId stored in the context, if it exists.
+func ContextGetUserId(ctx context.Context) (string, bool) {
+	val, ok := ctx.Value(ctxUserId).(string)
+	return val, ok
+}
+
+func addUserIdToContext(ctx context.Context, userId string) context.Context {
+	return context.WithValue(ctx, ctxUserId, userId)
+}
+
+// ContextGetProjectId return the ProjectID stored in the context, if it exists.
+func ContextGetProjectId(ctx context.Context) (string, bool) {
+	val, ok := ctx.Value(ctxProjectId).(string)
+	return val, ok
+}
+
+func addProjectIdToContext(ctx context.Context, projectId string) context.Context {
+	return context.WithValue(ctx, ctxProjectId, projectId)
+}

toolkit/server/middleware.go

@@ -0,0 +1,80 @@
+package server
+
+import (
+	"encoding/base64"
+	"io"
+	"net/http"
+	"strings"
+
+	"github.com/ucan-wg/go-ucan/delegation"
+	"github.com/ucan-wg/go-ucan/did"
+)
+
+type Middleware func(http.Handler) http.Handler
+
+func ExampleMiddleware(serviceDID did.DID) Middleware {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			ctx := r.Context()
+
+			tokenReader, ok := extractBearerToken(r)
+			if !ok {
+				http.Error(w, "missing or malformed UCAN HTTP Bearer token", http.StatusUnauthorized)
+				return
+			}
+
+			// decode
+			// TODO: ultimately, this token should be a container with one invocation and 1+ delegations.
+			//  We are doing something simpler for now.
+			dlg, err := delegation.FromDagCborReader(tokenReader)
+			if err != nil {
+				http.Error(w, "malformed UCAN delegation", http.StatusBadRequest)
+				return
+			}
+
+			// optional: http-bearer
+
+			// validate
+			if dlg.Subject() != serviceDID {
+				http.Error(w, "invalid UCAN delegation", http.StatusBadRequest)
+				return
+			}
+			// TODO: policies check + inject in context
+
+			// extract values
+			userId, err := dlg.Meta().GetString("userId")
+			if err != nil {
+				http.Error(w, "missing or malformed userId", http.StatusBadRequest)
+				return
+			}
+			projectId, err := dlg.Meta().GetString("projectId")
+			if err != nil {
+				http.Error(w, "missing or malformed projectId", http.StatusBadRequest)
+				return
+			}
+
+			// inject into context
+			ctx = addUserIdToContext(ctx, userId)
+			ctx = addProjectIdToContext(ctx, projectId)
+
+			next.ServeHTTP(w, r.WithContext(ctx))
+		})
+	}
+}
+
+func extractBearerToken(r *http.Request) (io.Reader, bool) {
+	header := r.Header.Get("Authorization")
+	if header == "" {
+		return nil, false
+	}
+
+	if !strings.HasPrefix(header, "Bearer ") {
+		return nil, false
+	}
+
+	// skip prefix
+	reader := strings.NewReader(header[len("Bearer "):])
+
+	// base64 decode
+	return base64.NewDecoder(base64.StdEncoding, reader), true
+}