exectx: add a minimal middleware to extract the HTTP bearer, and make the UCAN ctx

toolkit/server/exectx/middleware.go

@@ -0,0 +1,43 @@
+package exectx
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/INFURA/go-ucan-toolkit/server/bearer"
+)
+
+// Middleware returns an HTTP middleware tasked with:
+// - extracting UCAN credentials from the `Authorization: Bearer <data>` HTTP header
+// - performing basic checks, and returning HTTP errors if necessary
+// - exposing those credentials in the go context as a UcanCtx for further usage
+func Middleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ctn, err := bearer.ExtractBearerContainer(r.Header)
+		if errors.Is(err, bearer.ErrNoUcan) {
+			http.Error(w, "no UCAN auth", http.StatusBadRequest)
+			return
+		}
+		if errors.Is(err, bearer.ErrContainerMalformed) {
+			http.Error(w, "malformed token", http.StatusBadRequest)
+			return
+		}
+		if err != nil {
+			// should not happen, defensive programming
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		// prepare a UcanCtx from the container, for further evaluation in the server pipeline
+		ucanCtx, err := FromContainer(ctn)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		// insert into the go context
+		r = r.WithContext(AddUcanCtxToContext(r.Context(), ucanCtx))
+
+		next.ServeHTTP(w, r)
+	})
+}