feat: handle Docker Bearer token auth for upstream registries (#60)

Docker Hub (and other registries) return 401 with a `Www-Authenticate: Bearer realm=...` challenge even for public images. The proxy now:

1. Detects 401 + Bearer challenge
2. Parses realm/service/scope from the header
3. Fetches an anonymous token (or authenticated if username/password configured)
4. Retries the original request with the Bearer token

Fixes: `docker pull artifactapi.../dockerhub/library/redis:latest` returning "unauthorized: upstream returned 401"
Reviewed-on: #60
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

.woodpecker/docker.yaml

@@ -22,6 +22,8 @@ steps:
       repo: git.unkin.net/unkin/artifactapi-ui
       dockerfile: ui/Dockerfile.ui
       context: ui
+      build_args:
+        BASE_PATH: /ui
       username: droneci
       password:
         from_secret: DRONECI_PASSWORD

internal/api/v1/proxy.go

@@ -37,6 +37,20 @@ func (h *ProxyHandler) Routes() chi.Router {
 	return r
 }
 
+func (h *ProxyHandler) DockerV2Routes() chi.Router {
+	r := chi.NewRouter()
+	r.Get("/", h.handleDockerPing)
+	r.Head("/", h.handleDockerPing)
+	r.Get("/{remoteName}/*", h.handleProxy)
+	r.Head("/{remoteName}/*", h.handleProxy)
+	return r
+}
+
+func (h *ProxyHandler) handleDockerPing(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Docker-Distribution-Api-Version", "registry/2.0")
+	w.WriteHeader(http.StatusOK)
+}
+
 func (h *ProxyHandler) handleProxy(w http.ResponseWriter, r *http.Request) {
 	remoteName := chi.URLParam(r, "remoteName")
 	path := chi.URLParam(r, "*")

internal/proxy/engine.go

@@ -4,10 +4,12 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"io"
 	"log/slog"
 	"net/http"
+	"strings"
 	"time"
 
 	"git.unkin.net/unkin/artifactapi/internal/cache"
@@ -147,6 +149,21 @@ func (e *Engine) fetchFromUpstream(ctx context.Context, remote models.Remote, pa
 		return nil, &UpstreamError{Err: err}
 	}
 
+	if resp.StatusCode == http.StatusUnauthorized {
+		resp.Body.Close()
+		token, err := fetchBearerToken(ctx, resp.Header.Get("Www-Authenticate"), remote)
+		if err == nil && token != "" {
+			req2, _ := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+			req2.Header.Set("Authorization", "Bearer "+token)
+			resp, err = http.DefaultClient.Do(req2)
+			if err != nil {
+				return nil, &UpstreamError{Err: err}
+			}
+		} else {
+			return nil, &ProxyError{Status: http.StatusUnauthorized, Message: "upstream returned 401"}
+		}
+	}
+
 	if resp.StatusCode != http.StatusOK {
 		resp.Body.Close()
 		return nil, &ProxyError{Status: resp.StatusCode, Message: fmt.Sprintf("upstream returned %d", resp.StatusCode)}
@@ -319,6 +336,71 @@ func (r readerAt) ReadAt(p []byte, off int64) (n int, err error) {
 	return
 }
 
+func fetchBearerToken(ctx context.Context, wwwAuth string, remote models.Remote) (string, error) {
+	if !strings.HasPrefix(wwwAuth, "Bearer ") {
+		return "", fmt.Errorf("not a Bearer challenge")
+	}
+
+	params := map[string]string{}
+	for _, part := range strings.Split(wwwAuth[7:], ",") {
+		part = strings.TrimSpace(part)
+		eq := strings.Index(part, "=")
+		if eq < 0 {
+			continue
+		}
+		key := part[:eq]
+		val := strings.Trim(part[eq+1:], `"`)
+		params[key] = val
+	}
+
+	realm := params["realm"]
+	if realm == "" {
+		return "", fmt.Errorf("no realm in Bearer challenge")
+	}
+
+	tokenURL := realm
+	sep := "?"
+	if s, ok := params["service"]; ok {
+		tokenURL += sep + "service=" + s
+		sep = "&"
+	}
+	if s, ok := params["scope"]; ok {
+		tokenURL += sep + "scope=" + s
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, tokenURL, nil)
+	if err != nil {
+		return "", err
+	}
+
+	if remote.Username != "" && remote.Password != "" {
+		req.SetBasicAuth(remote.Username, remote.Password)
+	}
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("token endpoint returned %d", resp.StatusCode)
+	}
+
+	var tokenResp struct {
+		Token       string `json:"token"`
+		AccessToken string `json:"access_token"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
+		return "", err
+	}
+
+	if tokenResp.Token != "" {
+		return tokenResp.Token, nil
+	}
+	return tokenResp.AccessToken, nil
+}
+
 type ProxyError struct {
 	Status  int
 	Message string

internal/server/server.go

@@ -96,6 +96,7 @@ func (s *Server) routes() chi.Router {
 
 	proxyHandler := v1.NewProxyHandler(s.engine, s.virtEngine, s.db, s.store, s.localHandler)
 	r.Mount("/api/v1", proxyHandler.Routes())
+	r.Mount("/v2", proxyHandler.DockerV2Routes())
 
 	remotesHandler := v2.NewRemotesHandler(s.db)
 	virtualsHandler := v2.NewVirtualsHandler(s.db)

internal/virtual/engine.go

@@ -79,7 +79,7 @@ func (e *Engine) fetchMemberIndexes(ctx context.Context, virt models.Virtual, pa
 					results[idx] = result{err: fmt.Errorf("local index %q: %w", name, err)}
 					return
 				}
-				results[idx] = result{index: MemberIndex{RemoteName: name, RepoType: remote.RepoType, Body: body}}
+				results[idx] = result{index: MemberIndex{RemoteName: name, RepoType: remote.RepoType, BaseURL: remote.BaseURL, Body: body}}
 				return
 			}
 
@@ -102,7 +102,7 @@ func (e *Engine) fetchMemberIndexes(ctx context.Context, virt models.Virtual, pa
 				return
 			}
 
-			results[idx] = result{index: MemberIndex{RemoteName: name, RepoType: remote.RepoType, Body: body}}
+			results[idx] = result{index: MemberIndex{RemoteName: name, RepoType: remote.RepoType, BaseURL: remote.BaseURL, Body: body}}
 		}(i, memberName)
 	}
 

internal/virtual/helm_merger.go

@@ -54,15 +54,26 @@ func (m *HelmMerger) MergeIndexes(members []MemberIndex, proxyBaseURL string) ([
 				seen[chart][ver.Version] = true
 
 				if proxyBaseURL != "" {
+					routePrefix := "remote"
+					if member.RepoType == "local" {
+						routePrefix = "local"
+					}
+					baseHost := extractHost(member.BaseURL)
+
 					for i, u := range ver.URLs {
 						if strings.HasPrefix(u, "http://") || strings.HasPrefix(u, "https://") {
-							ver.URLs[i] = fmt.Sprintf("%s/api/v1/remote/%s/%s",
+							if baseHost != "" && extractHost(u) != baseHost {
+								continue
+							}
+							ver.URLs[i] = fmt.Sprintf("%s/api/v1/%s/%s/%s",
 								strings.TrimRight(proxyBaseURL, "/"),
+								routePrefix,
 								member.RemoteName,
 								extractPath(u))
 						} else {
-							ver.URLs[i] = fmt.Sprintf("%s/api/v1/remote/%s/%s",
+							ver.URLs[i] = fmt.Sprintf("%s/api/v1/%s/%s/%s",
 								strings.TrimRight(proxyBaseURL, "/"),
+								routePrefix,
 								member.RemoteName,
 								u)
 						}
@@ -78,6 +89,19 @@ func (m *HelmMerger) MergeIndexes(members []MemberIndex, proxyBaseURL string) ([
 	return yaml.Marshal(merged)
 }
 
+func extractHost(rawURL string) string {
+	idx := strings.Index(rawURL, "://")
+	if idx == -1 {
+		return ""
+	}
+	rest := rawURL[idx+3:]
+	slashIdx := strings.Index(rest, "/")
+	if slashIdx == -1 {
+		return rest
+	}
+	return rest[:slashIdx]
+}
+
 func extractPath(rawURL string) string {
 	idx := strings.Index(rawURL, "://")
 	if idx == -1 {

internal/virtual/merger.go

@@ -9,6 +9,7 @@ import (
 type MemberIndex struct {
 	RemoteName string
 	RepoType   models.RepoType
+	BaseURL    string
 	Body       []byte
 }
 

ui/Dockerfile.ui

@@ -6,13 +6,20 @@ COPY package.json package-lock.json* ./
 RUN npm ci
 
 COPY . .
+
+ARG BASE_PATH=/
+ENV BASE_PATH=${BASE_PATH}
 RUN npm run build
 
 FROM nginx:alpine
 
+ARG BASE_PATH=/
+
 COPY --from=builder /app/dist /usr/share/nginx/html
 COPY nginx.conf /etc/nginx/conf.d/default.conf
 
+RUN sed -i "s|\${BASE_PATH}|${BASE_PATH}|g" /etc/nginx/conf.d/default.conf
+
 EXPOSE 80
 
 CMD ["nginx", "-g", "daemon off;"]

ui/nginx.conf

@@ -5,33 +5,7 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
-    location /api/ {
-        proxy_pass http://artifactapi:8000;
-        proxy_set_header Host $host;
-        proxy_set_header X-Real-IP $remote_addr;
-        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
-        proxy_buffering off;
-    }
-
-    location /v2/ {
-        proxy_pass http://artifactapi:8000;
-        proxy_set_header Host $host;
-        proxy_set_header X-Real-IP $remote_addr;
-        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-        proxy_set_header X-Forwarded-Proto $scheme;
-        proxy_buffering off;
-    }
-
-    location /health {
-        proxy_pass http://artifactapi:8000;
-    }
-
-    location /metrics {
-        proxy_pass http://artifactapi:8000;
-    }
-
-    location / {
+    location ${BASE_PATH} {
         try_files $uri $uri/ /index.html;
     }
 }

ui/src/main.tsx

@@ -4,9 +4,13 @@ import { BrowserRouter } from 'react-router-dom';
 import { App } from './App';
 import './index.css';
 
+declare const __BASE_PATH__: string;
+
+const basename = __BASE_PATH__.replace(/\/+$/, '') || '/';
+
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <BrowserRouter>
+    <BrowserRouter basename={basename}>
       <App />
     </BrowserRouter>
   </StrictMode>,

ui/vite.config.ts

@@ -1,7 +1,10 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 
+const basePath = process.env.BASE_PATH || '/'
+
 export default defineConfig({
+  base: basePath,
   plugins: [react()],
   server: {
     proxy: {
@@ -11,4 +14,7 @@ export default defineConfig({
       '/metrics': 'http://localhost:8000',
     },
   },
+  define: {
+    '__BASE_PATH__': JSON.stringify(basePath),
+  },
 })